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

1 Answer
Dr. Hayek
Jan 7, 2016

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).
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