Question

My ion and O2 ions a
are isoelectronic in structure. Are they similar in
size? If not, why?
n​

Answer 1

Answer:

No, $O^{2-}$ is bigger in size than $Mg^{2+}$

Explanation:

size of any atom does not only depend on number of electrons, but it actually depends of Effective nuclear charge, i.e. $Z_{eff}$ and shielding of electrons.

In Mg2+ and O2- ion, the no. of electrons is same, but in Mg, protons are more as compared to O2-, and hence app;y more force on electrons and because no. of electrons is already less in Mg2+, electrons cannot compensate with the force and are attracted by protons and size becomes smaller.

The case is just opposite in O2-, here, no. of protons is less and electrons is more. So, due to repulsions b/w electrons, (which is greater than attraction of protons), electrons move away and size of atoms becomes bigger than the original.

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