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Periodic table trends
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Mini-video on ion size
Video transcript
In the video on solubility, I
draw little pictures of sodium and chloride ions when sodium
chloride dissolves or disassociates into water. This is sodium and
this is chloride. And my simple brain, when I
looked at it, I said, OK, how should I draw these things? I said, well, they're in the
same period, and sodium is a Group 1 element. It's an alkali metal, while
chlorine is a halogen, so chlorine's going to have a
smaller atomic radius. And the logic there, just to
review from the atomic table trends, is that both of their
valence electrons are in the third shell. Sodium only has 11 protons
pulling in the center. It has 11 in the center, and it
has only one electron out there in its valence shell. So the attraction isn't as
strong as the case of chlorine, which has 17 protons
in the center. Although it has more valence
electrons-- it has 7 of them-- these protons are going
to have a stronger attraction on them. So if you just look at the trend
in the periodic table, you'd expect the sodium neutral
atom to be bigger than the chlorine neutral atom. Because this guy has more
protons pulling everything in. And that's how I drew the
ions in that video. I said, oh, when I disassociate
in water, I'll have a big sodium ion and
a smaller chlorine ion, which is incorrect. Because think about-- and this
was pointed out to me by one of the viewers, and they're
correct, and I should have realized it. What happens when you
ionize these things? This guy will lose an
electron, right? He gives the electron
to this guy. So his electron configuration
is actually going to look a lot more like neon. He now will have no electrons
in that third shell, in the third energy state. So now he's going to have an
atomic radius that's actually much more similar to
neon here, right? Because he's going to have
filled up the second shelf. So actually, the sodium ion,
this is completely incorrect. The sodium ion is going to have
an atomic radius not that different than neon. Actually, it will be even a
little smaller than neon because it has the same electron
configuration, but it has one more proton. So the sodium ion is actually
going to be smaller. Because it gets rid of the
electron in that third shell, and the chlorine cation, gained
an electron, so it has completely completed
its third shell. So here you have where
the chlorine ion is going to be bigger. So in that solubility video, I
should've actually switched the places between the
sodium and the chlorine, at least in size-wise. And, of course, I showed how
they disassociate in water, and this would be attracted to
the oxygen end of the water, and you have the hydrogen
end and all that. But you can watch the solubility
video for that. It doesn't change the real
takeaway from the video. But I think this is a really
interesting point that it brings up, that when you ionize
these neutral atoms, it can significantly change,
especially significantly change their relative
atomic sizes. Anyway, hopefully, you found
that interesting.