Question

Why is a magnesium atom smaller than a sodium atom?

Answer 1

The Mg atom is smaller than Na as it has 1 more proton, which increases its effective nuclear charge. The nucleus exerts a greater force of attraction that brings the electrons closer inward, and so the atom is smaller. Mg is smaller than Ca because Ca has an extra electron shell. Also, the electrons in lower shells of Ca shields the valence electrons from the nuclear charge and so the atom can be bigger.

Learn more about Magnesium Hydroxide Formula http://goo.gl/UFK3aS

Answer 2

Mg is smaller than Ca because it has one less electron shell. The electron configurations are: Mg [Ne]3s2 and for Ca [Ar]4s2

Mg is smaller than Na because the extra electron is added to the same 3s shell (adding no extra volume), but there is an additional proton in the nucleus, creating a greater pull on the electron shells.