Question

How can a periodic table be used to determine the charge of an ion?

Answer 1

The Group number of main-group elements gives you the number of valence electrons.

Explanation:

Metals are reducing; they tend to lose electrons and are thus oxidized to cations. Thus Group I and Group II metals, the alkali metals, and alkaline earths, commonly have `+I` and `+II` oxidation states.

On the other hand, non-metals are oxidizing; they tend to gain electrons and are reduced to formal anions. Group VI, and Group VII elements, the chalcogens and the halogens, formally tend to gain 2 and 1 electrons respectively, and thus attain the electronic configuration of a Noble Gas. Thus oxygen and sulfur, Group VI elements, commonly form oxides and sulfides, where their oxidation state is `-II`. In the same way, the halogens, Group VII, tend to gain the 1 electron to form an halide ion (`-I`). Fluorine, in particular, is a ferocious oxidant.