On the periodic table, what is a group? For the main groups, what characteristic do the elements have in common?

In modern times, we know that the elements in a given group (also known as a family or column) have the same number of valence electrons, with ground state configurations having a consistent pattern, for instance:

F 1s2 2s2 2p5, Cl 1s2 2s2 2p6 3s2 3p5, Br 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p5, etc.

Of course, the ground state configurations play a major role in determining how an element reacts and what compounds it forms. Thus, the elements in a given group have similar properties.

The structure of the table also predicts how the properties vary. For instance, atomic radius increases down a group as does metallic character.

Explanation:

h let me think

particle   p is an electron and particle q is a neutron