Looking at charges on single-atom ions

In the periodic table, the roman numerals at the top of the A families show the number of valence electrons in each element.

Because atoms form ions to achieve full valence energy levels, that means you can often use an element’s position in the periodic table to figure out what kind of charge an ion normally has. Here’s how to match up the A families with the ions they form:

✓ IA family (alkali metals): Each element has one valence electron, so it loses a single electron to form a cation with a 1+ charge.

✓ IIA family (alkaline earth metals): Each element has two valence electrons, so it loses two electrons to form a 2+ cation.

✓ IIIA family: Each element has three valence electrons, so it loses three electrons to form a 3+ cation.

✓ VA family: Each element has five valence electrons, so it gains three electrons to form an anion with a 3– charge.

✓ VIA family: Each element has six valence electrons, so it gains two electrons to form an anion with a 2– charge.

✓ VIIA family (halogens): Each element has seven valence electrons, so it gains a single electron to form an anion with a 1– charge.

Determining the number of electrons that members of the transition metals (the B families) lose is more difficult. In fact, many of these elements lose a varying number of electrons so that they form two or more cations with different charges.