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Chemistry library
Unit 8: Lesson 2
Periodic table trends- Periodic trends
- Atomic radius trends on periodic table
- Atomic and ionic radii
- Mini-video on ion size
- Ionization energy trends
- Ionization energy: period trend
- First and second ionization energy
- Electron affinity: period trend
- Electronegativity
- Electronegativity and bonding
- Metallic nature
- Periodic trends and Coulomb's law
- Worked example: Identifying an element from successive ionization energies
- Ionization energy: group trend
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Mini-video on ion size
Correcting a mistake and learning a bit about ion size. Created by Sal Khan.
Want to join the conversation?
What is the difference between atomic radii and ionic radii(8 votes)
Is there a difference between the trends of the two? I know that Atomic radii increase down a group and right to left, could you please tell me the trend in the same format for ionic radii? I'm confused and I have SAT chemistry tomorrow.(1 vote)
I'm confused! In a video, Sal said that as an element gains electrons, it becomes smaller in size due to more attraction. But in this video, he says that as Na loses an electron, it's radius decreases, while the opposite happens when Cl gains an electron. Please help!(4 votes)
Also, when Na loses its outer most electron it loses that entire energy level making it smaller.(4 votes)
- In the video, Khan said that the atomic radius of Sodium Ion is going to be a lot like Na, if we ionize Na and Cl each other, because it loses an electron.
However, doesn't that mean Cl should get smaller, because Cl (as an anion) would gain one electron, which not only makes its atomic radius lot like Ar, but also going to attract those outer electrons because the more positive charges were added on Cl?
I don't understand how can Cl gets bigger in size-wise after it ionizes with Na?(4 votes)
Cl- has the same number of electrons as Ar, but it has less protons, so less of a positive charge pulling those electrons to the nucleus, so will has a larger radius.
Likewise Na+ has the same number of electrons as Ne, but it has 1 more proton so attracts all those electrons more strongly so has a smaller radius.(5 votes)
what is a ion(2 votes)- An ion is an atom or molecule that has does not have the same number of protons as it does electrons, so it has a charge.(5 votes)
So then why does Sodium have a larger atomic radius than Chlorine in elementary state, since they both have got the 3s Shell and Chlorine even the 3p ontop? Thanks for your help :)(2 votes)- The atomic radius is affected by many factors (and is itself only an estimate). Thus, it is not good to over-generalize about why one element has a different atomic radius than another.
However, one of the main reasons why Na has a larger atomic radius than Cl is because Cl has more protons, though they both are filling the n=3 shell. Thus, the electrons in the outermost shell of Cl experience a stronger attraction toward the nucleus (because the nucleus of Cl has a greater charge).(3 votes)
Would drawing the sizes different affect the equation at all?(3 votes)
What is difference between electronegativity and electropositivity ?(2 votes)- They’re essentially the same concept just one is the inverse of the other. Something that has a high electronegativity will have a low electropositivity and vice versa.(3 votes)
- At2:26, how do you know what to dram for the ion size?(2 votes)
These are just schematics (pictures not intended to realistically depict something or indicate actual values)!(2 votes)
- is there a limit as to how many substances can be combined?(1 vote)
- Are you thinking of chemical combining (reaction to form new substances) or just physical mixing? There is probably no limit to how many substances you can just mix together (think of making a salad--you could put in just about anything!), but there are physical rules that determine how substances react that could limit how you could combine them chemically. Not everything you mix together will react.(4 votes)
I understand why the sodium becomes smaller (it loses a whole shell), but why does the chlorine become bigger? Is this because there is a missing proton so there is no added pull towards the center?(1 vote)- The chlorine gets an electron, which is repelled by the other electrons in the valence shell. These electrons all want to be as far away from each other as they can, but are all attracted to the same nucleus. When you add an extra electron into the mix, the same attracting force of the 17 protons now has to deal with 18 electrons, which makes the outermost electron able to be further away from the nucleus.(3 votes)
2:26Video 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.