Losing an electron

A sodium atom carries 11 protons and 11 electrons. The charges cancel exactly, so the atom as a whole is electrically neutral.

Figure to be added

The sodium atom: 11 electrons arranged 2, 8, 1 in shells around a nucleus of 11 protons (figure 10.1).

The one electron in the way

Sodium has a low electronegativity — it holds its outer electron loosely. That lone electron in the third shell is the only thing standing between sodium and a full outer shell, and the cheapest way to deal with it is to let it go.

Na → Na⁺ + e⁻

A sodium atom becomes a sodium ion by releasing one electron.

What changed, and what did not

	Na atom	Na⁺ ion
Protons	11 (+11)	11 (+11)
Electrons	11 (−11)	10 (−10)
Configuration	2, 8, 1	2, 8
Overall charge	0	+1

The proton count never moves. Losing an electron removes one negative charge and leaves eleven positives against ten negatives, which is where the +1 comes from.

Figure to be added

A sodium atom releasing one electron to become a sodium ion, with the outermost shell now empty (figure 10.2).

Ion and cation

An atom that has acquired a charge is called an ion. An ion carrying a positive charge is a positive ion, or cation.

An ion is not its atom

The chemical properties of an ion differ from those of the atom it came from. Sodium metal reacts violently with water; sodium ions sit harmlessly dissolved in it. Do not read Na and Na⁺ as two names for the same thing.