What does a "group" in the periodic table refer to?

A "group" in the periodic table refers to a vertical column that contains elements with similar chemical properties and similar valence electron configurations. The elements in a group have the same number of outer electrons, which is a key factor in determining their reactivity and the types of chemical bonds they can form. For example, all elements in Group 1 have one outer electron, which makes them highly reactive metals.

The presence of the same number of outer electrons leads to similarities in how these elements interact with others, making it crucial for predicting chemical behavior. This characteristic is what truly defines a group in the periodic table, providing essential insight into the elements' properties and reactivity.