What is a charged group of atoms called?

Charged groups of atoms are ions. Ions consist of one or more atoms that have gained or lost electrons. If the group gains electrons, it has a negative charge, and if it loses electrons, it becomes positive.

Ions join with other ions of the opposite charge in order to share electrons and form a neutral compound. Na+ joins with Cl- to form sodium chloride, which is common table salt. Oxygen with a -2 charge combines with two H+ ions to form water. Some ion groups remain together as a single ion that join with ions of the opposite charge to form a neutral compound. The sulfate ion, which has a -2 charge, joins with two positively charged potassium ions to creat potassium sulfate.