Final answer:
Ions are classified based on whether they gain or lose electrons. An atom that loses electrons becomes a cation, while one that gains electrons becomes an anion. The charge is denoted by a superscript plus or minus sign.
Step-by-step explanation:
When classifying traits of ions, we consider whether an atom gains or loses electrons. An atom that loses electrons becomes a cation, which is a positively charged ion. For example, a sodium atom (Na), after losing one electron, becomes a sodium cation written as Na+. On the other hand, an atom that gains electrons becomes an anion, which is a negatively charged ion. Ions such as the fluoride ion are written with the element symbol followed by a superscript minus sign indicating a negative charge, such as F−. If an ion has a charge greater than one, it will have a number before the plus or minus sign, such as Mg2+ for a magnesium cation that has lost two electrons, or Se2− for a selenium anion that has gained two electrons.