coconut64
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#1
Report Thread starter 3 years ago
#1
Which ion has the smallest ionic radius?
A Cl−
B Ca2+
C K+
D S2−

Can someone explain why B is the answer? The mark scheme says because Ca has the most postive charge but I thought Cl- will be the smallest as it has less shielding and has the greatest nuclear charge..

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Pigster
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All of them = 1s2 2s2 2p6 3s2 3p6, therefore have the same shielding. Which has the most protons?
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Adam_1999
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Write out the electron configuration of each species: Cl- [Ne] 3s2 3p6 which is [Ar]
Ca2+ has the electron configuration of Argon, but with 2 more protons.
K+ and S2- have the same number of electrons as argon. In fact all of choices have the same number of electrons, but calcium has the most protons, therefore highest nuclear charge and therefore smallest ionic radius.

The overall charge on an ion has NOTHING to do with its ionic radius. Ionic radius depends only on the distance between the nucleus and the valence electrons (ie how many shells it has) and the nuclear charge (how many protons it has). This is a very common misconception!

https://youtu.be/U9t-slLl30E
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coconut64
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