Question

Why is a magnesium atom smaller than atoms of both sodium and calcium?

Answer 1

See explanation.

Explanation:

In order to answer this question, let us write the electron configuration of each element:

`""_11Na:1s^(2)2s^(2)2p^(6)3s^(1)`

`""_12Mg:1s^(2)2s^(2)2p^(6)3s^(2)`

`""_20Ca:1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)4s^(2)`

Looking at the electron configuration we conclude that:

• Magnesium atom is smaller than sodium atom because the nuclear charge of Magnesium (`12+`) is higher than that of Sodium (`11+`). Magnesium nucleus will attract the electrons more toward it and therefore, shrinking the size of the atom.
• Magnesium atom is smaller than Calcium atom because Calcium has more electron (`20e^-`) which will occupy more energy levels (`n=4` for Calcium versus `n=3` for Magnesium).