Summary
Highlights
Ions are simply charged atoms that acquire a positive or negative charge by gaining or losing electrons. Neutral atoms have an equal number of protons and electrons, resulting in no net charge.
Ions are formed when atoms either gain or lose electrons. Metals tend to lose electrons because they have low electronegativity (the ability to attract electrons). When an atom loses electrons, it forms a positively charged ion called a cation. For example, sodium loses one valence electron to form a positively charged sodium ion.
Non-metals tend to gain electrons due to their higher electronegativity. When an atom gains electrons, it forms a negatively charged ion called an anion. For instance, chlorine, a non-metal, can gain an electron to form a negatively charged chloride ion.
The number of electrons an atom gains or loses corresponds to its valence. The number of valence electrons (electrons in the outermost shell) can be determined by the group number in the periodic table of elements. Metals form cations and non-metals form anions.
Unlike cations, which are named after the parent atom, anions are named by taking the root name of the atom and changing the ending to '-ide'. For example, chlorine becomes chloride, and fluorine becomes fluoride.
The periodic table is useful for determining the type of ion formed. Group 1 metals form +1 ions, and Group 2 metals form +2 ions. Non-metals form negative ions by gaining electrons, with specific charges depending on their group (e.g., Group 17 forms -1 ions).
When a metal and a non-metal combine, they form an ionic compound. These compounds must have a net charge of zero. This means the number of positive ions (cations) and negative ions (anions) must balance out. For example, sodium ion (Na+) and chloride ion (Cl-) combine to form sodium chloride (NaCl) because their +1 and -1 charges cancel each other out.