monatomic ions
Monatomic ions form when a single atom gains or loses electrons. For the main group elements, cations are generally formed by removing all of the valence electrons from the atom. Since the numbers of valence electrons for the representative elements are constant within a particular group, all we need is the group number of a given element to know its charge when it becomes a cation. Group 1 elements form ions with a 1+ charge, Group 2 metal ions have a 2+ charge, and the ions of Group 13 elements tend to have a 3+ charge. Heavier p-block metals such as tin and lead are special cases and will be discussed with the transition metal ions. The name of a monatomic cation is the same as the name of the neutral element. For example, the sodium atom Na loses a single electron to form the sodium ion Na + , while Al 3+ is an aluminum ion.