1
00:00:17,416 --> 00:00:20,419
I want to start right
where we left off,

2
00:00:20,419 --> 00:00:24,857
which is in filling atoms,
filling electrons into atoms.

3
00:00:24,857 --> 00:00:30,796
We've done a lot of work to know
what it is that we're filling.

4
00:00:30,796 --> 00:00:34,066
We had to go all
the way to quantum

5
00:00:34,066 --> 00:00:38,337
to know what orbitals
are, not just orbits.

6
00:00:38,337 --> 00:00:39,872
Right.

7
00:00:39,872 --> 00:00:44,910
And we talked about the
four quantum numbers, right?

8
00:00:44,910 --> 00:00:48,781
And so now we're
going to use those,

9
00:00:48,781 --> 00:00:52,518
and we're going to use the
exclusion principle from Pauli

10
00:00:52,518 --> 00:00:54,053
and a few other things.

11
00:00:54,053 --> 00:00:56,622
And we're going to fill
electrons into atoms.

12
00:00:56,622 --> 00:00:59,658
So this is where we
left off on Monday.

13
00:00:59,658 --> 00:01:00,793
There they are, right?

14
00:01:00,793 --> 00:01:04,997
Remember, you know,
as I said on Monday,

15
00:01:04,997 --> 00:01:08,467
if we only had Bohr, what we
would have is the left hand

16
00:01:08,467 --> 00:01:11,070
side here, n equals 1.

17
00:01:11,070 --> 00:01:14,306
We would have just have
n equals 1, 2, 3, 4, 5,

18
00:01:14,306 --> 00:01:18,811
but we wouldn't have any of
this variation of l, right,

19
00:01:18,811 --> 00:01:23,049
like the p electrons,
the d electrons.

20
00:01:23,049 --> 00:01:25,283
That differentiation
came in when

21
00:01:25,283 --> 00:01:29,321
we solved the equations of
quantum mechanics, right,

22
00:01:29,321 --> 00:01:36,495
for an electron in feeling
the potential of the proton.

23
00:01:36,495 --> 00:01:38,229
And then the other
thing that happens

24
00:01:38,229 --> 00:01:40,933
is these things don't
line up necessarily

25
00:01:40,933 --> 00:01:43,335
exactly how you might
imagine, because there

26
00:01:43,335 --> 00:01:47,773
are complicated effects, right?

27
00:01:47,773 --> 00:01:51,509
It's not just a naive feeling.

28
00:01:51,509 --> 00:01:54,880
Instead there's these
effects like shielding.

29
00:01:54,880 --> 00:01:57,883
Right, so electrons all the
way out here in an atom,

30
00:01:57,883 --> 00:02:00,419
they don't necessarily
see all the protons.

31
00:02:00,419 --> 00:02:02,621
They're shielded.

32
00:02:02,621 --> 00:02:05,791
And then to make matters
even more complicated,

33
00:02:05,791 --> 00:02:11,163
these orbitals can wiggle
in with nodes, right?

34
00:02:11,163 --> 00:02:12,731
This is what we did
Monday, with nodes

35
00:02:12,731 --> 00:02:16,268
all the way in so they can
see-- some of these orbitals

36
00:02:16,268 --> 00:02:21,107
have a little bit of them
that see the protons up close.

37
00:02:21,107 --> 00:02:23,175
So we showed that with 2s.

38
00:02:23,175 --> 00:02:25,010
That's called
orbital penetration.

39
00:02:25,010 --> 00:02:28,147
And that's why these
things split up.

40
00:02:28,147 --> 00:02:31,450
They have the same principle
quantum number, n is 2,

41
00:02:31,450 --> 00:02:34,019
but this has a lower
energy than the 2p.

42
00:02:37,823 --> 00:02:43,028
But how is the electron
moving within this orbital?

43
00:02:43,028 --> 00:02:44,763
No.

44
00:02:44,763 --> 00:02:45,297
It's not.

45
00:02:45,297 --> 00:02:48,300
That's a classical way
of thinking, right?

46
00:02:48,300 --> 00:02:50,668
And it's so hard to
stop thinking that way.

47
00:02:50,668 --> 00:02:52,204
I know we want to
think that way.

48
00:02:52,204 --> 00:02:52,905
But it's not.

49
00:02:52,905 --> 00:02:56,575
An electron is being
in its orbital,

50
00:02:56,575 --> 00:03:00,312
because an orbital is a
probability distribution.

51
00:03:00,312 --> 00:03:01,480
All right?

52
00:03:01,480 --> 00:03:04,316
So the electron, all we
know from that orbital

53
00:03:04,316 --> 00:03:07,052
is that the electron has a
probability of being here

54
00:03:07,052 --> 00:03:10,422
sometimes and a probability
of being there other times.

55
00:03:10,422 --> 00:03:11,423
That's what it tells us.

56
00:03:11,423 --> 00:03:13,792
So we know that in that
2s orbital, sometimes

57
00:03:13,792 --> 00:03:17,596
it's really, really close
to those protons, right?

58
00:03:17,596 --> 00:03:19,431
That was that orbital
penetration, the peak

59
00:03:19,431 --> 00:03:21,066
that you saw on Monday.

60
00:03:21,066 --> 00:03:23,035
All right, so with all
that knowledge just kind

61
00:03:23,035 --> 00:03:24,570
of getting us back
in the mood here

62
00:03:24,570 --> 00:03:27,673
and our quantum numbers
and our Pauli exclusion,

63
00:03:27,673 --> 00:03:29,508
we're ready to fill.

64
00:03:29,508 --> 00:03:33,879
And the way that
we're going to start

65
00:03:33,879 --> 00:03:39,718
is the way that most chemistry
textbooks would start,

66
00:03:39,718 --> 00:03:43,689
which is with a very
simple rule, all right,

67
00:03:43,689 --> 00:03:45,991
called the aufbau principle.

68
00:03:45,991 --> 00:03:55,267
And aufbau means-- so aufbau
means filling up in German.

69
00:03:55,267 --> 00:04:00,439
And basically the idea
is that you fill--

70
00:04:03,108 --> 00:04:10,916
you fill from the lowest
levels, the lowest.

71
00:04:10,916 --> 00:04:12,751
Those are also the ground state.

72
00:04:12,751 --> 00:04:15,487
Right, the ground state
would be the lowest, right?

73
00:04:15,487 --> 00:04:25,297
That's the lowest energy, lowest
levels, ground state level,

74
00:04:25,297 --> 00:04:28,100
energy, and up.

75
00:04:28,100 --> 00:04:29,201
OK.

76
00:04:29,201 --> 00:04:35,007
And you use what is
called the n plus l rule.

77
00:04:37,509 --> 00:04:46,418
The n plus l rule means that
the ordering, the ordering

78
00:04:46,418 --> 00:04:50,322
of the orbital energies--

79
00:04:50,322 --> 00:04:58,264
orbital energies-- and let's
get a little more space here OK.

80
00:04:58,264 --> 00:05:02,434
The ordering of the
orbital energies

81
00:05:02,434 --> 00:05:13,445
increases with
increasing n plus l.

82
00:05:13,445 --> 00:05:16,181
All right, you fill from
the lowest energy up.

83
00:05:16,181 --> 00:05:18,517
So as my n plus
l, those are the--

84
00:05:18,517 --> 00:05:20,686
remember, that's the shape.

85
00:05:20,686 --> 00:05:23,789
This is sort of related to
the distance from the nucleus.

86
00:05:23,789 --> 00:05:25,324
This is the principle
quantum number.

87
00:05:25,324 --> 00:05:27,159
This is related to the
shape of the orbital.

88
00:05:27,159 --> 00:05:31,463
Right l, and as that number
increases, the energy,

89
00:05:31,463 --> 00:05:32,331
that's how you fill.

90
00:05:32,331 --> 00:05:37,169
Oh, but there's the case
where it might be the same.

91
00:05:37,169 --> 00:05:41,073
All right, so we have to
have another point here,

92
00:05:41,073 --> 00:05:45,344
which is when two orbitals--

93
00:05:45,344 --> 00:05:46,578
I did it again.

94
00:05:46,578 --> 00:05:48,213
I forgot my r.

95
00:05:48,213 --> 00:06:02,227
Two orbitals have the same
n plus l, then the lower n

96
00:06:02,227 --> 00:06:06,598
has lower e.

97
00:06:06,598 --> 00:06:09,868
OK, this is called
the n plus l rule,

98
00:06:09,868 --> 00:06:11,337
but rules are made to be broken.

99
00:06:11,337 --> 00:06:17,609
So as we're going to see, this
is actually really only true

100
00:06:17,609 --> 00:06:21,246
maybe 80% of the time.

101
00:06:21,246 --> 00:06:23,882
But we're going to use it,
because it is a good framework,

102
00:06:23,882 --> 00:06:25,751
and it captures--

103
00:06:25,751 --> 00:06:29,755
it gives us a way to start
thinking about electron

104
00:06:29,755 --> 00:06:30,789
occupation and atoms.

105
00:06:30,789 --> 00:06:33,692
And so if you take these
two points, this filling up

106
00:06:33,692 --> 00:06:35,894
and the ordering of
how you fill things,

107
00:06:35,894 --> 00:06:38,764
then you can draw this
as a very simple picture.

108
00:06:38,764 --> 00:06:40,899
This is from the
textbook Averill,

109
00:06:40,899 --> 00:06:44,403
right, where what you do
is you follow the arrows.

110
00:06:44,403 --> 00:06:48,140
OK, so you go this arrow,
I'm filling 1s, this arrow,

111
00:06:48,140 --> 00:06:49,641
then I go to 2s.

112
00:06:49,641 --> 00:06:51,076
Right, it's not going anywhere.

113
00:06:51,076 --> 00:06:53,712
So you go there, and
you keep following.

114
00:06:57,182 --> 00:07:03,088
OK, so 2s, 2p, so you'd
fill 1s, 2s, then 2p, right,

115
00:07:03,088 --> 00:07:06,191
because of the n plus
l rules is in effect.

116
00:07:06,191 --> 00:07:08,460
And then, OK, 3s.

117
00:07:08,460 --> 00:07:10,195
n is 3, l is 0.

118
00:07:10,195 --> 00:07:11,930
That's n plus 2 is 3.

119
00:07:11,930 --> 00:07:17,035
2p, 2p, n is 2, l
is 1, same value.

120
00:07:17,035 --> 00:07:18,737
But now I go to this
one here, and when

121
00:07:18,737 --> 00:07:21,807
they have the same value,
the lower n has lower energy.

122
00:07:21,807 --> 00:07:24,443
Lower n filled first.

123
00:07:24,443 --> 00:07:26,178
Filled first,
because the ordering

124
00:07:26,178 --> 00:07:29,214
is to go from lowest energy up.

125
00:07:29,214 --> 00:07:31,016
OK.

126
00:07:31,016 --> 00:07:34,920
All right, so that's our
rule, which will be broken.

127
00:07:37,589 --> 00:07:40,659
Now, how does this look?

128
00:07:40,659 --> 00:07:44,029
Well, if we do this, we're going
to get a little notation here

129
00:07:44,029 --> 00:07:46,832
and that's important,
if we do this,

130
00:07:46,832 --> 00:07:51,503
and we just do a few atoms
here, so for hydrogen, right,

131
00:07:51,503 --> 00:07:54,072
so for hydrogen we'd have--

132
00:07:54,072 --> 00:08:00,846
that's the 1s orbital, and we're
putting in one electron in it.

133
00:08:00,846 --> 00:08:02,314
Now, the notation
here is something

134
00:08:02,314 --> 00:08:03,615
that we're going to use a lot.

135
00:08:03,615 --> 00:08:07,252
So let me explain this.

136
00:08:07,252 --> 00:08:09,788
This is n.

137
00:08:09,788 --> 00:08:11,723
This is l.

138
00:08:11,723 --> 00:08:16,962
That's the l in, what,
spectroscopic notation, right?

139
00:08:16,962 --> 00:08:20,265
Remember we talked about
that Monday, right, s, p, d.

140
00:08:20,265 --> 00:08:22,267
OK.

141
00:08:22,267 --> 00:08:28,006
And then this is the
number of electrons.

142
00:08:28,006 --> 00:08:30,442
And so if we keep going
with this notation,

143
00:08:30,442 --> 00:08:34,446
then in the case of
helium, so for helium

144
00:08:34,446 --> 00:08:39,985
you would have 1s2, because
I fill a second electron

145
00:08:39,985 --> 00:08:41,986
into the 1s orbital.

146
00:08:41,986 --> 00:08:44,656
Now, this is where
Pauli comes in.

147
00:08:44,656 --> 00:08:46,558
Right, Paul said, OK, enough.

148
00:08:46,558 --> 00:08:50,028
You're done with that orbital,
because I've got two electrons.

149
00:08:50,028 --> 00:08:52,831
They do have different
quantum numbers.

150
00:08:52,831 --> 00:08:54,665
They've got the same n.

151
00:08:54,665 --> 00:08:57,402
Right, they've got the same l.

152
00:08:57,402 --> 00:09:00,405
Their m sub l's are
the same because there

153
00:09:00,405 --> 00:09:02,040
is no range here for s, right.

154
00:09:02,040 --> 00:09:05,210
Remember m sub l for s can
only be, you know, zero.

155
00:09:05,210 --> 00:09:10,015
But they have different
spins, up and down.

156
00:09:10,015 --> 00:09:13,318
And so sometimes, what
is also really useful,

157
00:09:13,318 --> 00:09:15,554
and we'll go back and forth
between these pictures,

158
00:09:15,554 --> 00:09:19,157
is you go back to what we drew,
you know, with the Bohr model,

159
00:09:19,157 --> 00:09:22,861
where we draw this in
terms of energy levels.

160
00:09:22,861 --> 00:09:25,597
And so if you drew this
in terms of energy levels,

161
00:09:25,597 --> 00:09:26,798
this is what'd you see.

162
00:09:26,798 --> 00:09:29,701
So you'd have like energy.

163
00:09:29,701 --> 00:09:31,703
And remember, in
the hydrogen atom,

164
00:09:31,703 --> 00:09:34,439
this is minus 13.6
electron volts.

165
00:09:34,439 --> 00:09:36,708
And so if you wanted to
draw this in this way,

166
00:09:36,708 --> 00:09:39,244
you would say, OK, there
is one electron there,

167
00:09:39,244 --> 00:09:41,947
and we'll-- remember, we said
you can draw electron spin with

168
00:09:41,947 --> 00:09:43,582
arrows.

169
00:09:43,582 --> 00:09:47,886
Right, whereas here, if we
drew this, then we draw--

170
00:09:47,886 --> 00:09:49,721
I'm not putting
the energy there.

171
00:09:49,721 --> 00:09:54,359
We don't know it, because Bohr
13.6 good for hydrogen. Right,

172
00:09:54,359 --> 00:09:55,193
but here--

173
00:09:55,193 --> 00:09:58,463
oh, and by the way, this
would be the 1s orbital.

174
00:09:58,463 --> 00:10:00,465
This would be the 1s orbital.

175
00:10:00,465 --> 00:10:04,570
But in this case, I've got two
electrons, one up, one down.

176
00:10:07,472 --> 00:10:09,708
And now, Pauli says you're done.

177
00:10:09,708 --> 00:10:10,208
All right.

178
00:10:10,208 --> 00:10:18,283
And so if you go to lithium,
then you have 1s2 2s1.

179
00:10:18,283 --> 00:10:21,587
And so if you drew this in
terms of an energy diagram,

180
00:10:21,587 --> 00:10:26,024
you'd have the 1s, and
we're putting that,

181
00:10:26,024 --> 00:10:28,927
and then you have the
2s somewhere up higher

182
00:10:28,927 --> 00:10:31,296
where we put one electron.

183
00:10:31,296 --> 00:10:35,133
Those are-- that's how you
would see these atoms in terms

184
00:10:35,133 --> 00:10:38,003
of the filling of the
electrons into their orbitals.

185
00:10:38,003 --> 00:10:38,870
Right.

186
00:10:38,870 --> 00:10:41,406
OK, good.

187
00:10:41,406 --> 00:10:44,109
Now, OK, let's keep going.

188
00:10:44,109 --> 00:10:46,378
So what we'll do is
we'll do this here.

189
00:10:46,378 --> 00:10:47,245
So let's see.

190
00:10:47,245 --> 00:10:53,318
So beryllium would be 1s2 2s2.

191
00:10:53,318 --> 00:11:03,261
And boron would be 1s2 2s2 2p1.

192
00:11:03,261 --> 00:11:05,130
OK, this is looking
good here, right?

193
00:11:05,130 --> 00:11:08,033
I'm really following aufbau now.

194
00:11:08,033 --> 00:11:11,269
Oh, I went that way,
then I went that way,

195
00:11:11,269 --> 00:11:12,904
and then I went up
here, and I started

196
00:11:12,904 --> 00:11:15,807
on this arrow, which is just
a way, graphically, of showing

197
00:11:15,807 --> 00:11:17,175
those rules.

198
00:11:17,175 --> 00:11:19,044
Good.

199
00:11:19,044 --> 00:11:23,281
Now, we get to carbon.

200
00:11:23,281 --> 00:11:25,984
And now we have to
think about this, right,

201
00:11:25,984 --> 00:11:33,925
because for carbon,
I've got 1s2 2s2 2p2.

202
00:11:33,925 --> 00:11:35,727
That is correct.

203
00:11:35,727 --> 00:11:36,261
All right.

204
00:11:36,261 --> 00:11:39,631
But if I think about this
in terms of the energy,

205
00:11:39,631 --> 00:11:48,807
1s2, 2s, right, well we
know from before, right, we

206
00:11:48,807 --> 00:11:52,377
know from before, like 2p.

207
00:11:52,377 --> 00:11:53,111
Where is 2p?

208
00:11:53,111 --> 00:11:53,945
There it is.

209
00:11:53,945 --> 00:11:57,015
It's got six electrons
that it can take.

210
00:11:57,015 --> 00:12:02,954
Because now m sub l can vary
from minus 1, 0, plus 1.

211
00:12:02,954 --> 00:12:05,924
Remember, that
corresponded to the three

212
00:12:05,924 --> 00:12:09,728
different orientations
of the p orbital.

213
00:12:09,728 --> 00:12:11,129
OK.

214
00:12:11,129 --> 00:12:13,699
But that means that
I've got three,

215
00:12:13,699 --> 00:12:16,935
so I can fill this
with 2, 2, and then

216
00:12:16,935 --> 00:12:19,037
the question is, what do I do?

217
00:12:19,037 --> 00:12:20,739
I don't know what to do.

218
00:12:20,739 --> 00:12:22,407
Do I do this?

219
00:12:22,407 --> 00:12:23,775
Is that right?

220
00:12:23,775 --> 00:12:25,343
No, somebody says.

221
00:12:25,343 --> 00:12:27,713
And that person knows
that the answer is no,

222
00:12:27,713 --> 00:12:29,414
because that person knows Hund.

223
00:12:29,414 --> 00:12:30,348
Where's Hund?

224
00:12:30,348 --> 00:12:32,784
There he is.

225
00:12:32,784 --> 00:12:34,886
Would have been more
dramatic had he appeared,

226
00:12:34,886 --> 00:12:37,122
but there he is,
because Hund came up

227
00:12:37,122 --> 00:12:42,427
with another rule, which
also is broken, sometimes.

228
00:12:42,427 --> 00:12:44,596
Not as much as aufbau.

229
00:12:44,596 --> 00:12:52,270
You know, so Hund said look,
when you have a case like this,

230
00:12:52,270 --> 00:13:00,445
electrons in the same p, so the
same like orbital, sub shell.

231
00:13:00,445 --> 00:13:05,016
OK, it's not the same sub
shell, but it's the same n 2p.

232
00:13:05,016 --> 00:13:05,884
Let's draw that.

233
00:13:05,884 --> 00:13:07,285
It is the same sub shell.

234
00:13:07,285 --> 00:13:08,754
I'm saying opposite things.

235
00:13:08,754 --> 00:13:12,157
2p, 2p.

236
00:13:12,157 --> 00:13:14,259
Shell, sub shell.

237
00:13:14,259 --> 00:13:16,294
But there are different
possibilities,

238
00:13:16,294 --> 00:13:18,563
and how you fill them
according to Hund

239
00:13:18,563 --> 00:13:22,200
is you maximize what's called
the multiplicity, which

240
00:13:22,200 --> 00:13:24,803
means that you want
the electrons to come

241
00:13:24,803 --> 00:13:29,307
in with the same spin
in different orbitals,

242
00:13:29,307 --> 00:13:32,010
in different p orbitals.

243
00:13:32,010 --> 00:13:33,411
That's how you fill them.

244
00:13:33,411 --> 00:13:34,179
Why?

245
00:13:34,179 --> 00:13:39,184
Well, that has to do with
more quantum mechanics,

246
00:13:39,184 --> 00:13:41,686
and it has to do with something
called exchange energy that's

247
00:13:41,686 --> 00:13:43,955
not part of what you
need to know about.

248
00:13:43,955 --> 00:13:46,324
And I'm not going
to teach it here.

249
00:13:46,324 --> 00:13:48,860
But you know, you can
think about it simply

250
00:13:48,860 --> 00:13:51,863
as the electrons
want to spread out,

251
00:13:51,863 --> 00:13:55,033
because they repel each
other in the same orbital.

252
00:13:55,033 --> 00:13:55,967
Right.

253
00:13:55,967 --> 00:13:58,069
They want a lot of
things, electrons.

254
00:13:58,069 --> 00:14:01,039
They want to be
close to protons.

255
00:14:01,039 --> 00:14:04,709
But they want to be kind
of not close to each other.

256
00:14:04,709 --> 00:14:06,344
They need their space.

257
00:14:06,344 --> 00:14:07,445
That's not a lot of things.

258
00:14:07,445 --> 00:14:08,513
It's two things.

259
00:14:08,513 --> 00:14:10,048
But that's what they want.

260
00:14:10,048 --> 00:14:13,852
And this allows them to maximize
that and lower their energy.

261
00:14:13,852 --> 00:14:15,253
And remember,
lowering your energy

262
00:14:15,253 --> 00:14:17,856
means happiness for electrons.

263
00:14:17,856 --> 00:14:20,992
So this is the preferred
way to fill, right?

264
00:14:20,992 --> 00:14:24,229
And that's what
Hund's rule tells us.

265
00:14:24,229 --> 00:14:28,333
Now, if you go to
silicon, and you say,

266
00:14:28,333 --> 00:14:30,001
well, OK, what does
silicon look like?

267
00:14:33,104 --> 00:14:34,873
All right, I'm going
to put silicon--

268
00:14:34,873 --> 00:14:37,275
no, don't do that.

269
00:14:37,275 --> 00:14:40,111
I'm going to put silicon
right underneath carbon,

270
00:14:40,111 --> 00:14:42,480
because I think it's an
interesting comparison.

271
00:14:42,480 --> 00:14:45,350
All right, so silicon is OK--

272
00:14:45,350 --> 00:14:50,388
1s2 2s2 2p6.

273
00:14:50,388 --> 00:14:52,090
They're all filled.

274
00:14:52,090 --> 00:14:58,763
Right, and then you go
to 3s2 and you go to 3p2.

275
00:14:58,763 --> 00:15:00,632
And this looks very
different than carbon,

276
00:15:00,632 --> 00:15:03,902
but actually, you can
abbreviate the notation,

277
00:15:03,902 --> 00:15:09,574
and we very often do in
these filling notation,

278
00:15:09,574 --> 00:15:10,675
and we do it this way.

279
00:15:10,675 --> 00:15:13,411
We say, well, this
has a neon core.

280
00:15:13,411 --> 00:15:16,581
So you go to the
nearest noble gas,

281
00:15:16,581 --> 00:15:18,950
not with more electrons,
because they're not there,

282
00:15:18,950 --> 00:15:20,585
with less electrons.

283
00:15:20,585 --> 00:15:24,055
You go to the nearest noble
gas, and say well, OK, that's

284
00:15:24,055 --> 00:15:25,490
basically neon.

285
00:15:25,490 --> 00:15:27,959
All right, this is neon.

286
00:15:27,959 --> 00:15:31,796
And so you can write
the notation is this--

287
00:15:31,796 --> 00:15:35,500
it's the same atom, just
a slightly abbreviated way

288
00:15:35,500 --> 00:15:37,969
of writing it, where I
would write, OK, this is

289
00:15:37,969 --> 00:15:43,341
a neon core with 3s2 and 3p2.

290
00:15:43,341 --> 00:15:47,445
Well, you can write that
with a helium core, 2s2 2p2.

291
00:15:47,445 --> 00:15:51,516
And what happens is you wind up
having a nice distinction here,

292
00:15:51,516 --> 00:15:55,086
because these are
core electrons.

293
00:15:55,086 --> 00:15:57,088
Remember, we're
filling electrons here.

294
00:15:57,088 --> 00:15:59,824
That's electrons.

295
00:15:59,824 --> 00:16:05,096
And these are called
valence electrons,

296
00:16:05,096 --> 00:16:10,535
and we'll be talking
about valence chemistry

297
00:16:10,535 --> 00:16:14,572
for the whole semester and what
these valence electrons do,

298
00:16:14,572 --> 00:16:16,975
right?

299
00:16:16,975 --> 00:16:18,944
And in fact, these
valence electrons,

300
00:16:18,944 --> 00:16:23,281
these ones on the outside
closest to the out--

301
00:16:23,281 --> 00:16:25,917
furthest away,
these are the ones

302
00:16:25,917 --> 00:16:29,287
that have all of the
chemistry that we care

303
00:16:29,287 --> 00:16:33,224
about in this class, chemistry.

304
00:16:33,224 --> 00:16:38,229
It's so important
that I went all caps.

305
00:16:38,229 --> 00:16:41,499
I'm not shouting,
but I went all caps.

306
00:16:41,499 --> 00:16:44,869
Whereas the core electrons
are kind of mostly inert.

307
00:16:44,869 --> 00:16:50,308
They're mostly inert,
chemically inert.

308
00:16:50,308 --> 00:16:55,513
OK, and so sometimes
it's very useful

309
00:16:55,513 --> 00:16:59,584
to write the notation
this way to see

310
00:16:59,584 --> 00:17:02,587
what do you got in the
valence, what's going on?

311
00:17:02,587 --> 00:17:04,155
Right, what does this valence--

312
00:17:04,155 --> 00:17:06,257
because then you start
to see similarities.

313
00:17:06,257 --> 00:17:11,997
The valence for lithium
and the valence for sodium

314
00:17:11,997 --> 00:17:13,865
look really similar.

315
00:17:13,865 --> 00:17:15,066
There's an outer s electron.

316
00:17:15,066 --> 00:17:17,335
That's the quantum number,
the principle quantum number

317
00:17:17,335 --> 00:17:18,036
is different.

318
00:17:18,036 --> 00:17:19,503
But the valence
looks very similar,

319
00:17:19,503 --> 00:17:21,906
one electron in an s orbital.

320
00:17:21,906 --> 00:17:25,143
And that allows us
to think intuitively

321
00:17:25,143 --> 00:17:27,712
about similarities
between elements,

322
00:17:27,712 --> 00:17:29,280
because if they have
the same valence,

323
00:17:29,280 --> 00:17:33,918
and the valence is responsible,
not same, but similar,

324
00:17:33,918 --> 00:17:36,921
similar shapes of orbitals,
different principal

325
00:17:36,921 --> 00:17:40,025
numbers, but if that's similar,
then maybe the chemistry

326
00:17:40,025 --> 00:17:42,660
those elements do
is also similar.

327
00:17:42,660 --> 00:17:45,063
This is a helpful way
to think about it.

328
00:17:45,063 --> 00:17:46,464
OK.

329
00:17:46,464 --> 00:17:48,933
I told you that rules
are meant to be broken,

330
00:17:48,933 --> 00:17:52,003
especially when we're
talking about n plus l,

331
00:17:52,003 --> 00:17:53,171
and it happens all the time.

332
00:17:53,171 --> 00:17:57,675
And there's two main reasons
or important reasons,

333
00:17:57,675 --> 00:18:00,211
and then there's a whole bunch
of other very complicated ones,

334
00:18:00,211 --> 00:18:02,313
that two I want
you to know about,

335
00:18:02,313 --> 00:18:05,183
which are exceptions
to this aufbau filling,

336
00:18:05,183 --> 00:18:07,852
OK, which are
exceptions to that,

337
00:18:07,852 --> 00:18:09,921
come in the
following situations.

338
00:18:09,921 --> 00:18:12,924
That you get stability--

339
00:18:12,924 --> 00:18:13,825
you get stability.

340
00:18:13,825 --> 00:18:16,094
That means lower energy
for the whole system.

341
00:18:16,094 --> 00:18:18,096
The system lowers
its energy and can

342
00:18:18,096 --> 00:18:23,768
be more stable when either
an orbital is fully filled--

343
00:18:23,768 --> 00:18:26,704
there it is, ns2, np6, nd10.

344
00:18:26,704 --> 00:18:28,706
You know those are fully
filled, because that's

345
00:18:28,706 --> 00:18:32,043
how many elections you can put
in each one, or half filled

346
00:18:32,043 --> 00:18:33,144
exactly.

347
00:18:33,144 --> 00:18:36,681
And so that's why in chromium
if you predict with aufbau,

348
00:18:36,681 --> 00:18:39,417
you would get 4s2
3d4, but actually you

349
00:18:39,417 --> 00:18:43,421
get 4s1 3d5, because you
can half fill both of those,

350
00:18:43,421 --> 00:18:45,890
and that adds to the stability.

351
00:18:45,890 --> 00:18:48,793
In copper, the predicted
one would be 4s2 3d9.

352
00:18:48,793 --> 00:18:53,098
But actually what you see is
a fully filled d shell, which

353
00:18:53,098 --> 00:18:56,234
adds to stability and
a half filled s shell.

354
00:18:56,234 --> 00:18:58,269
So it's willing to
make this trade off

355
00:18:58,269 --> 00:19:00,371
of a fully filled s
show for half filled.

356
00:19:00,371 --> 00:19:02,907
That's not a big trade off
to get the d, fully filled.

357
00:19:02,907 --> 00:19:06,010
OK, now there's more
complicated effects,

358
00:19:06,010 --> 00:19:12,650
all sorts of effects that
also lead to violations

359
00:19:12,650 --> 00:19:14,119
of the n plus l rule.

360
00:19:14,119 --> 00:19:17,455
I really hesitate to call it
a rule, given that, you know,

361
00:19:17,455 --> 00:19:20,458
there's a lot of
examples where it's not

362
00:19:20,458 --> 00:19:22,827
about the half filling
or the full filling.

363
00:19:22,827 --> 00:19:25,530
It's about complicated
interactions

364
00:19:25,530 --> 00:19:28,099
that have to do sometimes,
all the way with things

365
00:19:28,099 --> 00:19:31,402
like relativity, relativistic
effects, literally,

366
00:19:31,402 --> 00:19:38,209
of these electrons, which will
not be on any quiz or exam,

367
00:19:38,209 --> 00:19:41,579
with also the complexities that
happen with orbital penetration

368
00:19:41,579 --> 00:19:43,314
as you add more
and more electrons

369
00:19:43,314 --> 00:19:47,218
and the levels are kind
of closer together.

370
00:19:47,218 --> 00:19:51,055
They're a lot harder to see
clearly separate energies

371
00:19:51,055 --> 00:19:52,857
than in the first
two, three rows,

372
00:19:52,857 --> 00:19:54,492
as you go down in
the periodic table,

373
00:19:54,492 --> 00:19:56,294
those levels are closer
and closer together.

374
00:19:56,294 --> 00:19:57,695
So anomalies happen.

375
00:19:57,695 --> 00:19:58,696
But they're not really--

376
00:19:58,696 --> 00:20:01,065
I'm not sure we should call
them anomalies, because these

377
00:20:01,065 --> 00:20:04,702
are all exceptions to aufbau.

378
00:20:04,702 --> 00:20:06,604
So like I said, I want
you to know aufbau,

379
00:20:06,604 --> 00:20:08,039
because it's a
great way to start,

380
00:20:08,039 --> 00:20:12,577
but I also want you to know that
sometimes things switch around

381
00:20:12,577 --> 00:20:15,513
because of the effects that
we've been talking about.

382
00:20:15,513 --> 00:20:19,250
I don't expect you to memorize
all the exceptions to aufbau,

383
00:20:19,250 --> 00:20:20,351
OK?

384
00:20:20,351 --> 00:20:23,888
But I do want you to know about
these two key factors, which

385
00:20:23,888 --> 00:20:25,990
are half filling
and fully filling

386
00:20:25,990 --> 00:20:28,259
leading to enhanced stability.

387
00:20:28,259 --> 00:20:29,260
All right, good.

388
00:20:29,260 --> 00:20:31,462
OK, so we got valence.

389
00:20:31,462 --> 00:20:33,231
We got filling.

390
00:20:33,231 --> 00:20:39,170
Now, right away, right
away, all right--

391
00:20:39,170 --> 00:20:47,445
so by the way,
configurations are in here.

392
00:20:47,445 --> 00:20:48,546
It's a beautiful thing.

393
00:20:48,546 --> 00:20:52,283
When I look at this, I now
can look at this line in here

394
00:20:52,283 --> 00:20:53,985
that shows--

395
00:20:53,985 --> 00:20:58,122
that shows using this
notation, the filling

396
00:20:58,122 --> 00:21:01,659
of electrons for every single
atom, every single atom.

397
00:21:01,659 --> 00:21:06,130
And it's a beautiful thing
because it tells us so

398
00:21:06,130 --> 00:21:07,999
much about the periodic table.

399
00:21:07,999 --> 00:21:11,569
It tells us so much about
why the periodic table is

400
00:21:11,569 --> 00:21:12,270
what it is.

401
00:21:12,270 --> 00:21:14,005
It was arranged.

402
00:21:14,005 --> 00:21:19,477
Right, it was arranged because
of things like the combination,

403
00:21:19,477 --> 00:21:23,648
remember Mendeleev,
mass and properties.

404
00:21:23,648 --> 00:21:25,850
But now we see why.

405
00:21:25,850 --> 00:21:27,151
We see why.

406
00:21:27,151 --> 00:21:30,588
It's incredible, because
it goes back to counting.

407
00:21:30,588 --> 00:21:32,156
It literally goes
back to the quantum

408
00:21:32,156 --> 00:21:35,159
mechanical derivations
of orbitals

409
00:21:35,159 --> 00:21:36,694
and the principles
of filling them,

410
00:21:36,694 --> 00:21:38,296
and then the filling
them themselves.

411
00:21:38,296 --> 00:21:40,698
And you see, you know,
why does the lanthanides

412
00:21:40,698 --> 00:21:45,169
and actinides, why did
those things run for 14?

413
00:21:45,169 --> 00:21:46,537
Because that's
how many electrons

414
00:21:46,537 --> 00:21:48,673
go into the f orbitals.

415
00:21:48,673 --> 00:21:52,343
Right, that's how many
electrons go into 4f and 5f.

416
00:21:52,343 --> 00:21:53,911
That's why these are 14.

417
00:21:53,911 --> 00:21:57,715
Why are these two columns here?

418
00:21:57,715 --> 00:22:01,152
Why do those have similar
properties as you go down?

419
00:22:01,152 --> 00:22:03,821
Right, I mentioned
lithium and sodium, right.

420
00:22:03,821 --> 00:22:05,323
Well, because of
what we just said.

421
00:22:05,323 --> 00:22:07,292
You're increasing the
principle quantum number,

422
00:22:07,292 --> 00:22:09,460
but the valence chemistry
is very similar.

423
00:22:09,460 --> 00:22:11,929
They're all s.

424
00:22:11,929 --> 00:22:13,898
And we even call
them sometimes these

425
00:22:13,898 --> 00:22:18,102
blocks by the valence chemistry
that's getting filled.

426
00:22:18,102 --> 00:22:22,006
Right, so those first two
columns are the s block.

427
00:22:22,006 --> 00:22:23,541
Here over here,
they're the p block.

428
00:22:23,541 --> 00:22:26,644
It's not that these don't
have p electrons in them.

429
00:22:26,644 --> 00:22:28,446
It's that these are
the electrons that

430
00:22:28,446 --> 00:22:32,950
are getting added in this part,
in this region, whereas here,

431
00:22:32,950 --> 00:22:34,919
you've got d electrons.

432
00:22:34,919 --> 00:22:37,922
And now we know
exactly why this is 10.

433
00:22:37,922 --> 00:22:40,858
I mean, we know even more than
this, because aufbau says,

434
00:22:40,858 --> 00:22:43,828
why is this here and not here?

435
00:22:43,828 --> 00:22:46,497
Right, because of the
ordering of the filling,

436
00:22:46,497 --> 00:22:48,032
of the energies of the filling.

437
00:22:48,032 --> 00:22:51,235
These three d's come after 4s.

438
00:22:51,235 --> 00:22:52,970
That's why they're here.

439
00:22:52,970 --> 00:22:55,106
Right, that's why
they belong here.

440
00:22:55,106 --> 00:22:57,975
We now know so much more.

441
00:22:57,975 --> 00:23:01,045
We have so much more
insight into the ordering

442
00:23:01,045 --> 00:23:04,582
of the periodic table,
because of electron filling.

443
00:23:04,582 --> 00:23:07,352
And we'll be making
those connections.

444
00:23:07,352 --> 00:23:09,120
We'll be making those
connections a lot.

445
00:23:09,120 --> 00:23:12,523
Right, but I just wanted
to kind of show you

446
00:23:12,523 --> 00:23:15,760
the power of seeing things
in terms of filling.

447
00:23:15,760 --> 00:23:17,595
The one connection I'll
tell you about today

448
00:23:17,595 --> 00:23:19,130
has to do with diameter.

449
00:23:19,130 --> 00:23:20,998
OK, so we'll be
making connections

450
00:23:20,998 --> 00:23:23,701
all throughout the class
between electron filling

451
00:23:23,701 --> 00:23:25,536
and properties.

452
00:23:25,536 --> 00:23:30,341
Right, but let's start with a
simple one, how big is an atom?

453
00:23:30,341 --> 00:23:32,910
Well, now you can
understand some things.

454
00:23:32,910 --> 00:23:36,814
Right, so for example, if I plot
here or if Averill plots it,

455
00:23:36,814 --> 00:23:38,916
and I take that from
Averill and show it

456
00:23:38,916 --> 00:23:41,252
to you, the probability--

457
00:23:41,252 --> 00:23:44,622
remember we plotted
this before for 1s, 2s.

458
00:23:44,622 --> 00:23:48,259
Now, what they plot
here, OK, the 1s orbital

459
00:23:48,259 --> 00:23:50,995
for helium, that's got
two electrons in it.

460
00:23:50,995 --> 00:23:53,197
There it is right
there, the 1s, and then

461
00:23:53,197 --> 00:23:54,832
the 2s and 2p combined.

462
00:23:54,832 --> 00:23:56,934
Right, everything is sort
of thrown together here.

463
00:23:56,934 --> 00:24:00,204
They're not separated
for neon and then argon.

464
00:24:00,204 --> 00:24:04,108
So these are the first three
noble gases, helium, neon,

465
00:24:04,108 --> 00:24:04,909
argon.

466
00:24:04,909 --> 00:24:06,310
OK.

467
00:24:06,310 --> 00:24:07,445
And a couple of things.

468
00:24:07,445 --> 00:24:13,551
One thing you can see is that
the s electrons in helium

469
00:24:13,551 --> 00:24:15,686
are furthest out.

470
00:24:15,686 --> 00:24:18,856
And then the neon ones are
closer in, and look at that.

471
00:24:18,856 --> 00:24:20,591
The argon ones are even closer.

472
00:24:20,591 --> 00:24:22,493
Why?

473
00:24:22,493 --> 00:24:27,598
Why are the 1s electrons
getting closer in

474
00:24:27,598 --> 00:24:30,034
as I add more electrons?

475
00:24:30,034 --> 00:24:30,935
Right.

476
00:24:30,935 --> 00:24:33,838
Well, it has to do with
what we talked about Monday.

477
00:24:33,838 --> 00:24:36,707
Those 1s electrons
are not screened.

478
00:24:36,707 --> 00:24:39,844
So what they see as you go
from helium to neon to argon

479
00:24:39,844 --> 00:24:43,614
is more and more
positive charge.

480
00:24:43,614 --> 00:24:45,516
In fact, I've got
the numbers here,

481
00:24:45,516 --> 00:24:49,153
if you look at the
1s electron energy,

482
00:24:49,153 --> 00:24:53,791
remember for hydrogen, 13.6.

483
00:24:53,791 --> 00:24:55,693
Now remember, I didn't
write a value there.

484
00:24:55,693 --> 00:24:56,894
But there's two protons.

485
00:24:56,894 --> 00:25:00,231
So that 1s electron for helium.

486
00:25:00,231 --> 00:25:06,871
So if we take 1s electron
energy, so much abbreviation.

487
00:25:06,871 --> 00:25:10,241
For helium, it's 24.5 eV.

488
00:25:10,241 --> 00:25:11,876
That's how much it would take.

489
00:25:11,876 --> 00:25:14,745
So we can put minus, if you
want to compare with this,

490
00:25:14,745 --> 00:25:16,113
right, this minus 13.6.

491
00:25:16,113 --> 00:25:17,548
That's also how
much it would take

492
00:25:17,548 --> 00:25:20,651
to ionize that 1s electron.

493
00:25:20,651 --> 00:25:22,086
That's where it sits.

494
00:25:22,086 --> 00:25:31,762
But if you look at neon,
neon is minus 869.5 eV.

495
00:25:31,762 --> 00:25:37,401
And argon is minus 3,206 eV.

496
00:25:37,401 --> 00:25:38,903
That is a lot of energy.

497
00:25:38,903 --> 00:25:40,204
That is a lot more energy.

498
00:25:40,204 --> 00:25:42,206
That is much, much happier.

499
00:25:42,206 --> 00:25:44,842
If energy-- if lower
energy is happiness,

500
00:25:44,842 --> 00:25:47,211
those 1s electrons
are super happy,

501
00:25:47,211 --> 00:25:50,214
and they get closer to
all that positive charge.

502
00:25:50,214 --> 00:25:55,319
But you can also understand
why, like neon is larger

503
00:25:55,319 --> 00:25:59,323
than helium, and argon, even
though these energies of the 1s

504
00:25:59,323 --> 00:26:01,526
are closer and closer,
these are still

505
00:26:01,526 --> 00:26:07,298
going to be larger, because
as you go down in a column,

506
00:26:07,298 --> 00:26:09,800
you add a whole shell.

507
00:26:09,800 --> 00:26:11,435
Right, so I can't--

508
00:26:11,435 --> 00:26:13,604
right, so remember,
here's my plus charge.

509
00:26:13,604 --> 00:26:15,606
Here's my minus charge.

510
00:26:15,606 --> 00:26:18,242
I can't-- this is 1s.

511
00:26:18,242 --> 00:26:20,611
Now I can't add
anything in here.

512
00:26:20,611 --> 00:26:24,882
I got to add stuff
out here and go out.

513
00:26:24,882 --> 00:26:29,620
Remember those principle
quantum numbers, 1 to 2?

514
00:26:29,620 --> 00:26:32,890
Right, we don't need the
s here, just 1 to 2 to 3,

515
00:26:32,890 --> 00:26:35,726
they're going to push you
further and further out.

516
00:26:35,726 --> 00:26:37,094
We talked about that Monday.

517
00:26:37,094 --> 00:26:39,463
So now the next
electrons that come

518
00:26:39,463 --> 00:26:43,467
in in neon's case in 2s or 2p
or in argon's case, 3s and 3p,

519
00:26:43,467 --> 00:26:45,202
those are going to
come much further out.

520
00:26:45,202 --> 00:26:48,806
That's why when you look
at size, which is what's

521
00:26:48,806 --> 00:26:51,576
shown here, you see this trend.

522
00:26:51,576 --> 00:26:52,209
All right.

523
00:26:52,209 --> 00:26:55,813
So you see this trend that
as you go down a column, here

524
00:26:55,813 --> 00:26:56,547
they are.

525
00:26:56,547 --> 00:26:57,114
Here they are.

526
00:26:57,114 --> 00:27:00,017
So this is the size
in the periodic table,

527
00:27:00,017 --> 00:27:02,119
and these are calculated.

528
00:27:02,119 --> 00:27:03,020
These are calculated.

529
00:27:03,020 --> 00:27:04,021
Why are they calculated?

530
00:27:04,021 --> 00:27:07,124
Because you can see, this should
be pretty hard to measure.

531
00:27:07,124 --> 00:27:10,294
Right, these are hard to
measure unless the atoms are

532
00:27:10,294 --> 00:27:14,298
in like a solid, and
they're bonded together.

533
00:27:14,298 --> 00:27:17,234
So measured atomic
radii are often

534
00:27:17,234 --> 00:27:20,204
taking half of a bond length.

535
00:27:20,204 --> 00:27:22,873
But we can also calculate them.

536
00:27:22,873 --> 00:27:25,409
And that's why these are
calculated atomic radii.

537
00:27:25,409 --> 00:27:26,644
So these have no bonding.

538
00:27:26,644 --> 00:27:29,013
They're just isolated,
and they're calculated

539
00:27:29,013 --> 00:27:32,216
and there's helium,
neon, and argon.

540
00:27:32,216 --> 00:27:32,950
OK, fine.

541
00:27:32,950 --> 00:27:34,518
So we just understood that.

542
00:27:34,518 --> 00:27:37,054
And we understood this
arrow that the radii

543
00:27:37,054 --> 00:27:39,590
get larger as you go
down the periodic table.

544
00:27:39,590 --> 00:27:41,892
But what about going across?

545
00:27:41,892 --> 00:27:43,260
Why?

546
00:27:43,260 --> 00:27:46,263
I'm adding stuff to the atom.

547
00:27:46,263 --> 00:27:49,266
I'm filling lithium here.

548
00:27:49,266 --> 00:27:56,240
I'm adding an electron and from
lithium there to beryllium.

549
00:27:56,240 --> 00:27:58,175
How can it get smaller?

550
00:27:58,175 --> 00:27:59,176
Right.

551
00:27:59,176 --> 00:28:01,078
How can it get smaller?

552
00:28:01,078 --> 00:28:03,981
So that has to do--

553
00:28:03,981 --> 00:28:04,715
what did I do?

554
00:28:09,453 --> 00:28:11,555
OK, I'm going over here.

555
00:28:11,555 --> 00:28:12,256
All right.

556
00:28:12,256 --> 00:28:15,092
So that has to do
with the fact--

557
00:28:15,092 --> 00:28:17,194
with the same things that
we've been talking about.

558
00:28:17,194 --> 00:28:20,731
It has to do with the fact
that as I go from lithium.

559
00:28:20,731 --> 00:28:21,932
So OK, let's do this.

560
00:28:21,932 --> 00:28:26,303
If I have hydrogen,
and I go to lithium,

561
00:28:26,303 --> 00:28:28,305
you know that it's
going to be larger

562
00:28:28,305 --> 00:28:31,642
for the reasons I just said.

563
00:28:31,642 --> 00:28:36,213
But if I go from lithium over
to beryllium, it gets smaller.

564
00:28:39,650 --> 00:28:42,453
And the reason is
because of exactly this.

565
00:28:42,453 --> 00:28:49,727
If I go from hydrogen to
lithium, I add protons.

566
00:28:49,727 --> 00:28:52,396
But I shield those
protons with electrons.

567
00:28:52,396 --> 00:28:57,468
OK, but if I am at lithium,
let's see, lithium is here.

568
00:28:57,468 --> 00:29:00,504
So I've got one, two, three.

569
00:29:00,504 --> 00:29:02,707
And I've got an electron here.

570
00:29:02,707 --> 00:29:05,976
Right, I've got two
electrons in the 1s orbital,

571
00:29:05,976 --> 00:29:10,848
and then I've got one
electron in the 2s orbital.

572
00:29:10,848 --> 00:29:13,050
OK, so that's lithium.

573
00:29:13,050 --> 00:29:15,219
But now I go to beryllium.

574
00:29:15,219 --> 00:29:21,992
And if I'm beryllium,
I've got four.

575
00:29:21,992 --> 00:29:26,530
OK, and so now I've got
those 2s electrons here.

576
00:29:26,530 --> 00:29:30,634
But see-- I'm sorry, 1s.

577
00:29:30,634 --> 00:29:34,872
But in the 2s orbital, I
can put a second electron.

578
00:29:34,872 --> 00:29:38,909
Right, and so what happens
is those two electrons

579
00:29:38,909 --> 00:29:42,546
in the 2s orbital, they don't
really screen each other.

580
00:29:42,546 --> 00:29:45,916
They are screened
by the 1s orbital.

581
00:29:45,916 --> 00:29:47,251
So if I now--

582
00:29:47,251 --> 00:29:51,822
because I went-- even
though I added an electron,

583
00:29:51,822 --> 00:29:54,725
I also have a lot
more charge here.

584
00:29:54,725 --> 00:29:57,762
Right, and because these
two don't screen each other,

585
00:29:57,762 --> 00:30:02,199
but these two do, right, these
are going to be closer in,

586
00:30:02,199 --> 00:30:03,534
because they're more attracted.

587
00:30:03,534 --> 00:30:07,571
They're only screened
by these two electrons.

588
00:30:07,571 --> 00:30:10,941
So the additional
positive charge wins.

589
00:30:10,941 --> 00:30:13,811
If I go down in
quantum number, then I

590
00:30:13,811 --> 00:30:16,947
get a whole shelf
filled to screen.

591
00:30:16,947 --> 00:30:19,216
But here, I'm just
adding another electron

592
00:30:19,216 --> 00:30:22,019
to the same orbital
to the 2s orbital.

593
00:30:22,019 --> 00:30:24,321
But I've got a hold other
proton, and the shielding,

594
00:30:24,321 --> 00:30:26,857
the screening is the same.

595
00:30:26,857 --> 00:30:30,427
That's why beryllium is
smaller than lithium,

596
00:30:30,427 --> 00:30:32,029
even though you've
added an electron.

597
00:30:32,029 --> 00:30:35,399
And it's why the trend goes
like this, increasing that way,

598
00:30:35,399 --> 00:30:37,434
decreasing that way.

599
00:30:37,434 --> 00:30:41,405
Now, I like dancing.

600
00:30:41,405 --> 00:30:44,141
And so I like this
dancing analogy,

601
00:30:44,141 --> 00:30:47,778
because I love thinking
about atoms as dancing.

602
00:30:47,778 --> 00:30:50,080
I told you about the disco
and the periodic table.

603
00:30:50,080 --> 00:30:52,850
But you can take that
all the way to the atom.

604
00:30:52,850 --> 00:30:56,453
So you know, you can imagine
that you're an electron,

605
00:30:56,453 --> 00:30:58,889
and you see a proton.

606
00:30:58,889 --> 00:31:02,259
OK, so dance pairs are happy.

607
00:31:02,259 --> 00:31:06,430
Dancers are happy if they have
more people to dance with.

608
00:31:06,430 --> 00:31:08,532
And so if I'm hydrogen,
and I'm an electron,

609
00:31:08,532 --> 00:31:12,002
and I see a proton, protons
can only dance with electrons.

610
00:31:12,002 --> 00:31:13,470
And then I say, OK, let's dance.

611
00:31:13,470 --> 00:31:15,639
And you kind of start moving,
you know, a little bit.

612
00:31:15,639 --> 00:31:20,344
And but now, I'm
going to go to helium.

613
00:31:20,344 --> 00:31:22,913
So there's another
dancer in the middle,

614
00:31:22,913 --> 00:31:26,250
and someone comes on, and says,
oh OK, that's cool, right.

615
00:31:26,250 --> 00:31:26,851
I can--

616
00:31:26,851 --> 00:31:30,754
Now, either one of us can
dance with either one of those.

617
00:31:30,754 --> 00:31:32,556
All right, so I've got
two different people.

618
00:31:32,556 --> 00:31:35,659
I'm happier closer in.

619
00:31:35,659 --> 00:31:37,494
We can get close,
because there's choices

620
00:31:37,494 --> 00:31:40,731
for who you can dance with.

621
00:31:40,731 --> 00:31:42,466
All right.

622
00:31:42,466 --> 00:31:48,405
So that's why you get helium
much smaller than hydrogen.

623
00:31:48,405 --> 00:31:49,874
More people to dance with.

624
00:31:49,874 --> 00:31:51,876
Now you're lithium,
and you come along,

625
00:31:51,876 --> 00:31:54,311
and I'm a lithium
electron here, and I'm

626
00:31:54,311 --> 00:31:56,113
like I want to
dance with somebody.

627
00:31:56,113 --> 00:31:57,014
Who's there?

628
00:31:57,014 --> 00:31:59,884
And there's only one person,
because these two people

629
00:31:59,884 --> 00:32:01,652
are totally occupied.

630
00:32:01,652 --> 00:32:04,021
I only have one
possibility for people

631
00:32:04,021 --> 00:32:08,425
to dance with if I'm
this lithium electron.

632
00:32:08,425 --> 00:32:13,163
Right, but now I come in, and
I'm beryllium, and these two

633
00:32:13,163 --> 00:32:14,531
electrons, and
they're both like,

634
00:32:14,531 --> 00:32:17,234
well, OK, you guys are
blocking, whatever.

635
00:32:17,234 --> 00:32:18,702
That's not cool.

636
00:32:18,702 --> 00:32:20,304
But there's four
people in the middle.

637
00:32:20,304 --> 00:32:22,806
So there's always two
or three people, right,

638
00:32:22,806 --> 00:32:24,041
that we can dance with.

639
00:32:24,041 --> 00:32:25,075
That wasn't like a move.

640
00:32:25,075 --> 00:32:26,510
I don't know what that was.

641
00:32:26,510 --> 00:32:29,713
But I'm like I can dance with
you or I can dance with you.

642
00:32:29,713 --> 00:32:34,885
And more dancing
choices, happier.

643
00:32:34,885 --> 00:32:38,822
Happier, lower energy.

644
00:32:38,822 --> 00:32:40,357
So that's how I
like to see atoms.

645
00:32:43,160 --> 00:32:47,264
OK, so that's one example
of filling and screening

646
00:32:47,264 --> 00:32:53,837
and dancing, where this kind
of picture of the atoms,

647
00:32:53,837 --> 00:32:59,209
this electron filling of the
orbitals explains what we see.

648
00:32:59,209 --> 00:33:02,947
OK, now, we talked
about ionization,

649
00:33:02,947 --> 00:33:07,284
and we talked about how
sometimes those outer electrons

650
00:33:07,284 --> 00:33:12,589
can be lost, or sometimes,
maybe an atom would

651
00:33:12,589 --> 00:33:15,225
gain an outer electron.

652
00:33:15,225 --> 00:33:20,564
If an electron is lost from
an atom, called an ion.

653
00:33:20,564 --> 00:33:35,045
And so a charged atom
is an ion, and a cation

654
00:33:35,045 --> 00:33:40,517
is a positive charge,
positive charge.

655
00:33:40,517 --> 00:33:42,419
Abbreviations.

656
00:33:42,419 --> 00:33:44,888
Right, and so here's
sodium, and it's

657
00:33:44,888 --> 00:33:49,159
got all those dancers in there,
and it has lost an electron.

658
00:33:49,159 --> 00:33:50,227
There it is.

659
00:33:50,227 --> 00:33:51,762
It's going to lose--

660
00:33:51,762 --> 00:33:54,898
remember we talked about the
first ionization potential.

661
00:33:54,898 --> 00:33:56,166
We talked about that last week.

662
00:33:56,166 --> 00:33:59,169
It's going to lose that lowest--

663
00:33:59,169 --> 00:34:01,005
sorry, the highest
energy electron,

664
00:34:01,005 --> 00:34:03,240
the least bound
electron, the one that's

665
00:34:03,240 --> 00:34:05,442
all the way out there.

666
00:34:05,442 --> 00:34:07,611
And so if it does, it's NA plus.

667
00:34:07,611 --> 00:34:10,981
OK, gesundheit.

668
00:34:10,981 --> 00:34:12,282
Now, you can also--

669
00:34:12,282 --> 00:34:13,183
this is from Averill.

670
00:34:13,183 --> 00:34:15,819
You can also lose
more than that.

671
00:34:15,819 --> 00:34:18,722
All right, magnesium
might lose two electrons.

672
00:34:18,722 --> 00:34:20,724
So the gray part
here is the ion,

673
00:34:20,724 --> 00:34:24,094
and the blue part is the
original neutral atom,

674
00:34:24,094 --> 00:34:25,262
all right.

675
00:34:25,262 --> 00:34:28,364
And you can see that if
sodium loses one electron,

676
00:34:28,364 --> 00:34:30,199
and magnesium loses
two, those actually

677
00:34:30,199 --> 00:34:32,101
have the same
number of electrons.

678
00:34:32,101 --> 00:34:33,270
They're different atoms.

679
00:34:33,270 --> 00:34:36,572
Those are called isoelectronic.

680
00:34:36,572 --> 00:34:38,475
Well, you can also
gain electrons.

681
00:34:38,475 --> 00:34:39,576
So if you write that down.

682
00:34:39,576 --> 00:34:42,312
So you know, if
you gain electrons,

683
00:34:42,312 --> 00:34:44,815
does anybody know
what those are called?

684
00:34:44,815 --> 00:34:52,389
Anion, OK, negative charge
would be in an anion.

685
00:34:52,389 --> 00:34:55,958
OK, and I can ask question.

686
00:34:55,958 --> 00:34:58,862
If I lose an electron, it
makes sense that I got smaller.

687
00:34:58,862 --> 00:35:00,130
This is the radius.

688
00:35:00,130 --> 00:35:02,099
And if I gain, it make
sense that I got bigger.

689
00:35:02,099 --> 00:35:04,034
And I can mix it up.

690
00:35:04,034 --> 00:35:09,239
So I could ask you a question,
like what's the ordering--

691
00:35:09,239 --> 00:35:13,343
what's the ordering
of these atoms.

692
00:35:13,343 --> 00:35:20,784
Right, I could say, well, if
I had Mg 2 plus and Ca 2 plus,

693
00:35:20,784 --> 00:35:25,522
and Ca, what's the
ordering of their size?

694
00:35:25,522 --> 00:35:27,991
You now know how to answer
questions like this, right?

695
00:35:27,991 --> 00:35:30,260
If I lose electrons, I'm
going to get smaller.

696
00:35:30,260 --> 00:35:32,129
If I gain electrons,
I'm going to get bigger.

697
00:35:32,129 --> 00:35:38,435
But I also know that
for example, Ca 2 plus

698
00:35:38,435 --> 00:35:44,541
is smaller than Ca, and
Ca is bigger than Mg.

699
00:35:44,541 --> 00:35:45,008
Right.

700
00:35:45,008 --> 00:35:50,547
And so Ca 2 plus is going
to be bigger than Mg 2 plus.

701
00:35:50,547 --> 00:35:52,816
Right, that makes
a lot of sense.

702
00:35:52,816 --> 00:35:53,750
Done.

703
00:35:53,750 --> 00:35:54,918
You can order them now.

704
00:35:54,918 --> 00:35:58,355
All right, so Ca must be
bigger than Ca 2 plus,

705
00:35:58,355 --> 00:36:00,023
and that must be
bigger than Mg 2 plus.

706
00:36:00,023 --> 00:36:03,293
So we can think about now
adding in ions to the mix.

707
00:36:03,293 --> 00:36:05,195
And we're doing
this for a reason.

708
00:36:05,195 --> 00:36:08,899
All right, we're doing
this for a reason.

709
00:36:08,899 --> 00:36:16,206
But because, you see, some atoms
really don't mind doing this.

710
00:36:16,206 --> 00:36:16,940
They really don't.

711
00:36:16,940 --> 00:36:18,575
Sodium is one of them.

712
00:36:18,575 --> 00:36:19,776
They don't mind losing atoms.

713
00:36:19,776 --> 00:36:21,478
I mean, yeah, the
electron is there.

714
00:36:21,478 --> 00:36:25,315
But it's kind of there as
sort of like, I could be here,

715
00:36:25,315 --> 00:36:26,416
I can be there.

716
00:36:26,416 --> 00:36:27,317
I'm good.

717
00:36:27,317 --> 00:36:29,486
Whereas those 1s
electrons, you know

718
00:36:29,486 --> 00:36:31,421
the 1s electrons are
argon, are like you just

719
00:36:31,421 --> 00:36:33,223
try to take me out.

720
00:36:33,223 --> 00:36:36,193
All right, no way.

721
00:36:36,193 --> 00:36:37,661
But we will.

722
00:36:37,661 --> 00:36:41,431
We will ionize those next week.

723
00:36:41,431 --> 00:36:43,700
But for now, we're taking
these outer ones out

724
00:36:43,700 --> 00:36:46,303
that may not be
strongly balanced.

725
00:36:46,303 --> 00:36:48,939
They're happy,
losing or gaining.

726
00:36:48,939 --> 00:36:50,307
And how do you know?

727
00:36:50,307 --> 00:36:51,208
How do you know?

728
00:36:51,208 --> 00:36:55,812
If you have ions, how
do you know, you know,

729
00:36:55,812 --> 00:36:56,713
whether you have them?

730
00:36:56,713 --> 00:37:00,083
Well, here's the
deal, you now know

731
00:37:00,083 --> 00:37:02,886
a way to tell because in
this goodie bag, which I'll

732
00:37:02,886 --> 00:37:04,788
talk about in a few
minutes, you actually

733
00:37:04,788 --> 00:37:09,726
have the most accurate
measuring device ever made.

734
00:37:09,726 --> 00:37:10,961
You have a scale.

735
00:37:10,961 --> 00:37:12,829
That's not-- no.

736
00:37:12,829 --> 00:37:14,464
It's in here somewhere.

737
00:37:14,464 --> 00:37:18,835
You have a conductivity
meter, somewhere in here,

738
00:37:18,835 --> 00:37:21,271
which I cannot find.

739
00:37:21,271 --> 00:37:23,807
And the conductivity
meter is exactly that.

740
00:37:23,807 --> 00:37:24,641
There it is.

741
00:37:24,641 --> 00:37:28,245
Oh, look at this.

742
00:37:28,245 --> 00:37:29,179
This is incredible.

743
00:37:29,179 --> 00:37:31,915
So you can put this
into a solution,

744
00:37:31,915 --> 00:37:33,650
and it literally
just measures-- it's

745
00:37:33,650 --> 00:37:35,485
got two electrodes
that go in there,

746
00:37:35,485 --> 00:37:37,554
and it measures whether
there's any conduction,

747
00:37:37,554 --> 00:37:39,990
and you can see, well,
if I've got charge

748
00:37:39,990 --> 00:37:44,461
species in the solution,
ions, then this will tell you,

749
00:37:44,461 --> 00:37:47,130
because they'll help
conduct electricity.

750
00:37:47,130 --> 00:37:52,569
So you now have a way of knowing
when you have ions or not.

751
00:37:52,569 --> 00:37:55,405
OK, so that's good.

752
00:37:55,405 --> 00:37:58,375
But you see, the thing is
something very important

753
00:37:58,375 --> 00:38:01,878
happens when atoms
come together--

754
00:38:01,878 --> 00:38:04,514
when atoms-- don't
measure anything yet.

755
00:38:04,514 --> 00:38:05,782
But take it to lunch.

756
00:38:05,782 --> 00:38:07,784
Take it to lunch.

757
00:38:07,784 --> 00:38:09,319
You don't know.

758
00:38:09,319 --> 00:38:10,787
People talk about electrolytes.

759
00:38:10,787 --> 00:38:12,689
They talk a big game.

760
00:38:12,689 --> 00:38:13,156
All right.

761
00:38:13,156 --> 00:38:21,231
Now, the thing is when
atoms react, when--

762
00:38:21,231 --> 00:38:25,402
this sounds like the
beginning of a novel.

763
00:38:25,402 --> 00:38:32,709
When atoms react,
right, sometimes they

764
00:38:32,709 --> 00:38:34,911
will gain or lose.

765
00:38:34,911 --> 00:38:40,717
When atoms react, they
may want to gain or lose

766
00:38:40,717 --> 00:38:51,328
the amount of electrons to get
them to the closest noble gas.

767
00:38:51,328 --> 00:38:56,099
OK, closest noble gas.

768
00:38:56,099 --> 00:38:57,901
Now, that's really important.

769
00:38:57,901 --> 00:38:59,936
We just talked about how
you use the noble gas

770
00:38:59,936 --> 00:39:01,705
notation-- did I just erase it?

771
00:39:01,705 --> 00:39:04,574
I did.

772
00:39:04,574 --> 00:39:07,477
Because that could
be chemically inert.

773
00:39:07,477 --> 00:39:09,846
And we can only go down
when we do the notation,

774
00:39:09,846 --> 00:39:12,115
but now we can go up,
because I could add electrons

775
00:39:12,115 --> 00:39:15,118
to get to the nearest noble
gas, in terms of reacting.

776
00:39:15,118 --> 00:39:16,653
And look at this.

777
00:39:16,653 --> 00:39:20,023
If sodium is an atom that
doesn't mind losing electrons

778
00:39:20,023 --> 00:39:23,760
and chlorine is an atom that
really wants to gain electrons,

779
00:39:23,760 --> 00:39:27,864
and they come together,
and they come together,

780
00:39:27,864 --> 00:39:30,367
then you can form a bond.

781
00:39:30,367 --> 00:39:33,403
Oh, oh boy.

782
00:39:33,403 --> 00:39:35,672
Here we are I guaranteed you.

783
00:39:35,672 --> 00:39:38,308
I told you on Monday,
we would get here.

784
00:39:38,308 --> 00:39:40,777
I said, it's our three
week anniversary,

785
00:39:40,777 --> 00:39:44,114
and I think we're going to bond.

786
00:39:44,114 --> 00:39:49,219
First bond, first bond.

787
00:39:49,219 --> 00:39:51,154
And it's ionic.

788
00:39:51,154 --> 00:39:51,788
It's ionic.

789
00:39:55,992 --> 00:40:08,405
Because this is a bond of
an electrostatic attraction.

790
00:40:08,405 --> 00:40:11,541
This is the bond of
electrostatic attraction

791
00:40:11,541 --> 00:40:16,980
between two oppositely
charged atoms.

792
00:40:16,980 --> 00:40:30,160
So between two
oppositely charged atoms.

793
00:40:30,160 --> 00:40:32,996
And so if I've got a
positive and a negative,

794
00:40:32,996 --> 00:40:34,197
they're going to be attracted.

795
00:40:34,197 --> 00:40:35,665
How are they going
to be attracted?

796
00:40:35,665 --> 00:40:38,268
Well, actually
that's an attraction

797
00:40:38,268 --> 00:40:39,669
that we know all about.

798
00:40:39,669 --> 00:40:40,303
Oh there it is.

799
00:40:40,303 --> 00:40:40,804
Hold up.

800
00:40:40,804 --> 00:40:42,205
We just made our first bond.

801
00:40:42,205 --> 00:40:43,440
Let's talk about it.

802
00:40:43,440 --> 00:40:44,841
What do I want to say?

803
00:40:44,841 --> 00:40:46,476
I want to talk about
that attraction.

804
00:40:46,476 --> 00:40:47,944
Because that's
actually attraction

805
00:40:47,944 --> 00:40:48,912
that we know very well.

806
00:40:48,912 --> 00:40:50,547
It's a Coulomb attraction.

807
00:40:50,547 --> 00:40:53,316
Right, and so the
way this works is

808
00:40:53,316 --> 00:40:56,052
if I'm an atom with
positive charge,

809
00:40:56,052 --> 00:40:58,588
and I'm an atom with
negative charge.

810
00:40:58,588 --> 00:41:01,024
All right, so let's
take that same example,

811
00:41:01,024 --> 00:41:02,025
and this is the energy.

812
00:41:05,695 --> 00:41:08,131
And this is say, zero.

813
00:41:08,131 --> 00:41:11,935
And this is the distance
between the two atoms.

814
00:41:11,935 --> 00:41:15,338
If I'm out here, then
maybe the distance

815
00:41:15,338 --> 00:41:20,477
between sodium and
chlorine is very far.

816
00:41:20,477 --> 00:41:22,512
But you see there's
a Coulomb attraction.

817
00:41:22,512 --> 00:41:27,451
And so the attraction
is Coulomb,

818
00:41:27,451 --> 00:41:29,853
which is going to be
minus a constant times

819
00:41:29,853 --> 00:41:37,060
the charges on those ions over
the distance between them.

820
00:41:37,060 --> 00:41:38,728
All right.

821
00:41:38,728 --> 00:41:40,797
So that-- if I draw
that attraction,

822
00:41:40,797 --> 00:41:50,907
this is the charges on
ions, charges on ions.

823
00:41:50,907 --> 00:41:54,277
And if I draw that, the Coulomb
attraction looks like this.

824
00:41:54,277 --> 00:41:55,011
That's it.

825
00:41:55,011 --> 00:41:57,113
Right, that's 1 over r.

826
00:41:57,113 --> 00:41:59,449
But see, the thing is
if they get too close,

827
00:41:59,449 --> 00:42:03,453
then those core, you know,
then things start to repel.

828
00:42:03,453 --> 00:42:05,021
It's like, whoa, whoa.

829
00:42:05,021 --> 00:42:05,822
Hold on.

830
00:42:05,822 --> 00:42:08,658
I'm not going to go
any further, because I

831
00:42:08,658 --> 00:42:13,630
don't like having the same
charges getting too close,

832
00:42:13,630 --> 00:42:14,531
right.

833
00:42:14,531 --> 00:42:15,298
I don't like that.

834
00:42:15,298 --> 00:42:17,667
Your electrons are getting
too close to my electrons,

835
00:42:17,667 --> 00:42:20,837
and don't make me go nuclear.

836
00:42:20,837 --> 00:42:24,307
And so what you get is you
get something like this.

837
00:42:27,544 --> 00:42:32,516
And this would be the potential
energy of those two ions.

838
00:42:32,516 --> 00:42:34,584
They can't get
super duper close.

839
00:42:34,584 --> 00:42:37,020
But when they're far away,
they're kind of free, and then

840
00:42:37,020 --> 00:42:38,388
as they get a
little closer, they

841
00:42:38,388 --> 00:42:40,924
start feeling that attraction,
that Coulomb attraction.

842
00:42:40,924 --> 00:42:47,430
And this energy here,
this energy has a name.

843
00:42:47,430 --> 00:42:57,040
It's called the lattice energy,
because for the solid, right?

844
00:42:57,040 --> 00:43:03,547
So if I make a solid out
of these types of ions,

845
00:43:03,547 --> 00:43:06,049
and now I break it all up,
and I go all the way out

846
00:43:06,049 --> 00:43:09,619
to just loan ion, so
I go from the isolated

847
00:43:09,619 --> 00:43:15,825
ions to a solid of these ionic
bonds, then I gain this energy.

848
00:43:15,825 --> 00:43:18,695
And it takes that energy
to break them back up.

849
00:43:18,695 --> 00:43:20,063
That's called the
lattice energy.

850
00:43:20,063 --> 00:43:21,431
And you can see
right away, there

851
00:43:21,431 --> 00:43:24,734
are some really kind of
interesting observations

852
00:43:24,734 --> 00:43:28,004
you can make related to
this simple relationship

853
00:43:28,004 --> 00:43:31,374
of a Coulomb attraction
for an ionic bond.

854
00:43:31,374 --> 00:43:34,344
All right, so here's
two ionic solids.

855
00:43:34,344 --> 00:43:35,579
There's sodium chloride.

856
00:43:35,579 --> 00:43:36,546
There's magnesium oxide.

857
00:43:36,546 --> 00:43:39,916
There's Na plus and F minus.

858
00:43:39,916 --> 00:43:42,919
OK, and notice the
Coulomb energy here.

859
00:43:42,919 --> 00:43:44,921
And notice the differences
in the lattice energy.

860
00:43:44,921 --> 00:43:47,924
This is like four times that.

861
00:43:47,924 --> 00:43:52,862
That is exactly what you get
from this, because in this case

862
00:43:52,862 --> 00:43:55,932
Q1 and Q2 are both 1,
right, 1 and negative 1.

863
00:43:55,932 --> 00:44:00,637
And here, Q1 and Q2 are
both 2, and negative 2.

864
00:44:00,637 --> 00:44:03,740
So it should be four times,
and that's, in fact, you

865
00:44:03,740 --> 00:44:06,409
can measure how much energy does
it take to break this thing up,

866
00:44:06,409 --> 00:44:07,377
four times as much.

867
00:44:07,377 --> 00:44:08,878
That's the lattice energy.

868
00:44:08,878 --> 00:44:10,246
So we know something about this.

869
00:44:10,246 --> 00:44:12,515
And you can see trends.

870
00:44:12,515 --> 00:44:14,217
Right, so these
are now the radii.

871
00:44:14,217 --> 00:44:16,953
We just talked about these.

872
00:44:16,953 --> 00:44:20,123
Right, radii for ions.

873
00:44:20,123 --> 00:44:22,058
And this is the lattice energy.

874
00:44:22,058 --> 00:44:25,428
And you can see that if I'm the
smallest one, and the smallest

875
00:44:25,428 --> 00:44:27,330
one there, I have the
highest lattice energy.

876
00:44:27,330 --> 00:44:29,332
And that's the 1 over r part.

877
00:44:29,332 --> 00:44:32,902
So you got the charge and
how close they can get.

878
00:44:32,902 --> 00:44:35,605
And you now know from-- just
from the trends we've just

879
00:44:35,605 --> 00:44:39,175
talked about, the radii
trends we just talked about,

880
00:44:39,175 --> 00:44:43,713
you know how you might compare
how much one ionic solid

881
00:44:43,713 --> 00:44:46,783
is bonded, compared to
another, because you

882
00:44:46,783 --> 00:44:50,186
can talk about how much
charge it might lose or gain.

883
00:44:50,186 --> 00:44:54,824
It likes to get close to
the nearest noble gas.

884
00:44:54,824 --> 00:44:57,560
And you can also think about
their size or relative sizes.

885
00:44:57,560 --> 00:44:59,696
So like the largest
one with the largest

886
00:44:59,696 --> 00:45:05,001
has a larger r, and so
weaker lattice energy.

887
00:45:05,001 --> 00:45:07,070
And boy, is this important.

888
00:45:07,070 --> 00:45:09,839
It changes all sorts of
things about the properties

889
00:45:09,839 --> 00:45:15,578
of these solids, and that's
why, we developed the goodie bag

890
00:45:15,578 --> 00:45:17,547
to help you explore that.

891
00:45:17,547 --> 00:45:19,215
So you have different solids.

892
00:45:19,215 --> 00:45:21,584
They're not all
ionic, because you're

893
00:45:21,584 --> 00:45:23,720
talking about another
kind of solid next week.

894
00:45:23,720 --> 00:45:25,388
Right, but you've got
some ionic solids.

895
00:45:25,388 --> 00:45:27,857
And look, like, you
know, so a lot of them

896
00:45:27,857 --> 00:45:31,127
dissolve, but if the
lattice energy is so high,

897
00:45:31,127 --> 00:45:32,228
maybe it doesn't dissolve.

898
00:45:32,228 --> 00:45:34,197
Or maybe it's
harder to dissolve.

899
00:45:34,197 --> 00:45:34,931
How do you know?

900
00:45:34,931 --> 00:45:37,300
Well, you could see
it if you stir it.

901
00:45:37,300 --> 00:45:38,668
All right.

902
00:45:38,668 --> 00:45:40,303
But you also may
be able to measure.

903
00:45:40,303 --> 00:45:42,338
Are there ions in solution?

904
00:45:42,338 --> 00:45:44,240
If there are ions
in solution, than it

905
00:45:44,240 --> 00:45:49,045
could be a dissolved ionic
solid that you've made.

906
00:45:49,045 --> 00:45:51,314
And so-- oh hardness,
Mohs' scale.

907
00:45:51,314 --> 00:45:52,315
You can look that up.

908
00:45:52,315 --> 00:45:55,051
Did something scratch
something else?

909
00:45:55,051 --> 00:45:55,752
Right.

910
00:45:55,752 --> 00:45:57,153
That's what that's related to.

911
00:45:57,153 --> 00:45:58,788
Melting point,
right, the properties

912
00:45:58,788 --> 00:46:03,860
depend on this ionic bond.

913
00:46:03,860 --> 00:46:06,262
OK so there's the goodie
bag, and then I'll

914
00:46:06,262 --> 00:46:08,531
do my why this matters in
the last couple of minutes

915
00:46:08,531 --> 00:46:09,065
of class.

916
00:46:09,065 --> 00:46:10,600
All right, so there's
the goodie bag.

917
00:46:10,600 --> 00:46:12,268
Oh, you've got a
conductivity meter.

918
00:46:12,268 --> 00:46:14,504
You've got a scale.

919
00:46:14,504 --> 00:46:15,271
You've got a scale.

920
00:46:18,174 --> 00:46:20,376
I used to give that scale
out with white powder right

921
00:46:20,376 --> 00:46:22,912
before Thanksgiving for
a different goodie bag,

922
00:46:22,912 --> 00:46:25,081
and it was a really bad idea.

923
00:46:25,081 --> 00:46:28,918
But now it was--

924
00:46:28,918 --> 00:46:31,921
it was citric acid, lime juice.

925
00:46:31,921 --> 00:46:34,824
But people traveled like that.

926
00:46:34,824 --> 00:46:36,025
And so we've learned.

927
00:46:36,025 --> 00:46:37,160
We've learned.

928
00:46:37,160 --> 00:46:39,529
And so we give it to you
now, but please keep it.

929
00:46:39,529 --> 00:46:41,197
It's the world's
most accurate scale.

930
00:46:41,197 --> 00:46:42,265
Why does this matter?

931
00:46:42,265 --> 00:46:45,368
Because look-- you're going
to need the scale again.

932
00:46:45,368 --> 00:46:47,737
So please keep it.

933
00:46:47,737 --> 00:46:48,304
Here you go.

934
00:46:48,304 --> 00:46:50,573
Here's another chart
of ionic bonds.

935
00:46:50,573 --> 00:46:52,809
These are lattice energies.

936
00:46:52,809 --> 00:46:56,412
OK, these are lattice energies,
oh kilojoules per mole,

937
00:46:56,412 --> 00:46:57,680
it's just per mole of stuff.

938
00:46:57,680 --> 00:46:59,215
Right, don't get
confused by that.

939
00:46:59,215 --> 00:47:02,285
Joules, electron volts,
energies, per mole

940
00:47:02,285 --> 00:47:04,921
is per mole of atoms, right?

941
00:47:04,921 --> 00:47:08,792
OK, so we can isolate it down
to one bond or a mole of bonds.

942
00:47:08,792 --> 00:47:12,929
All right, 15,000 for aluminum.

943
00:47:12,929 --> 00:47:13,563
Look at that.

944
00:47:13,563 --> 00:47:16,399
That's why aluminum
is in your toothpaste.

945
00:47:16,399 --> 00:47:17,934
Aluminum oxide is
in your toothpaste.

946
00:47:17,934 --> 00:47:19,702
It's in your pans.

947
00:47:19,702 --> 00:47:21,304
It's in sandpaper.

948
00:47:21,304 --> 00:47:23,706
It is a very hard material.

949
00:47:23,706 --> 00:47:24,974
It is a very hard material.

950
00:47:24,974 --> 00:47:25,608
Why?

951
00:47:25,608 --> 00:47:26,810
Because of this.

952
00:47:26,810 --> 00:47:27,811
Literally.

953
00:47:27,811 --> 00:47:31,447
Those Q's are
really high, right?

954
00:47:31,447 --> 00:47:32,715
Why does this matter?

955
00:47:32,715 --> 00:47:36,052
Well, I'm going to give you
an example in hemodialysis.

956
00:47:36,052 --> 00:47:37,887
Hemodialysis is
something that people

957
00:47:37,887 --> 00:47:39,255
have to go into a hospital.

958
00:47:39,255 --> 00:47:44,694
People in their kidneys, don't
clean their blood efficiently

959
00:47:44,694 --> 00:47:47,964
or enough have to have
it cleaned by a machine,

960
00:47:47,964 --> 00:47:50,733
and 650,000 patients
suffer from this

961
00:47:50,733 --> 00:47:53,469
and go to a hospital
for literally four

962
00:47:53,469 --> 00:47:56,005
hours, three times a week.

963
00:47:56,005 --> 00:47:59,542
It devastates their
weekly schedule.

964
00:47:59,542 --> 00:48:02,111
And if you could
make this portable,

965
00:48:02,111 --> 00:48:05,348
you would change lives
in a really big way.

966
00:48:05,348 --> 00:48:06,616
One of the big--

967
00:48:06,616 --> 00:48:09,118
there are people out
there trying to do this.

968
00:48:09,118 --> 00:48:12,822
This is an example of a design
for a portable hemodialysis

969
00:48:12,822 --> 00:48:13,456
machine.

970
00:48:13,456 --> 00:48:17,260
One of the single biggest
drawbacks in making it portable

971
00:48:17,260 --> 00:48:20,296
is making a filter, because
you're filtering blood.

972
00:48:20,296 --> 00:48:22,732
You're filtering toxins
out of the blood.

973
00:48:22,732 --> 00:48:24,567
It's something that
the body can't do.

974
00:48:24,567 --> 00:48:27,670
So you need to do it for them.

975
00:48:27,670 --> 00:48:30,406
But the filters get
mucked up and gunked up,

976
00:48:30,406 --> 00:48:32,775
and they're not strong enough,
and they can't be cleaned.

977
00:48:32,775 --> 00:48:34,110
And look at this one.

978
00:48:34,110 --> 00:48:36,679
Here is a filter
made out of aluminum.

979
00:48:36,679 --> 00:48:40,316
All right, and these
things are what's needed.

980
00:48:40,316 --> 00:48:44,220
We need super strong,
super resilient new filters

981
00:48:44,220 --> 00:48:45,922
that can filter
things like blood

982
00:48:45,922 --> 00:48:47,523
and toxins out of the blood.

983
00:48:47,523 --> 00:48:49,926
So very, very tiny sizes
that we can make over

984
00:48:49,926 --> 00:48:51,961
large areas and uniformly.

985
00:48:51,961 --> 00:48:53,663
This is the kind of
starting material

986
00:48:53,663 --> 00:48:55,698
that we need to
make new filters,

987
00:48:55,698 --> 00:48:56,866
and it all comes back down.

988
00:48:56,866 --> 00:48:58,601
Why would that be
a good one if we

989
00:48:58,601 --> 00:49:00,169
can overcome it's brittleness?

990
00:49:00,169 --> 00:49:02,071
Because of the Q's.

991
00:49:02,071 --> 00:49:04,774
Because of the atom sizes,
because of everything

992
00:49:04,774 --> 00:49:06,242
that we talked about today.

993
00:49:06,242 --> 00:49:10,713
So have a great long weekend,
and see you guys next week.