Metal atoms become ions primarily through the process of losing electrons. When a metal atom is involved in a chemical reaction, it can lose one or more of its valence electrons. This loss of electrons transforms the neutral atom into a positively charged ion, known as a cation.
The reason metals tend to lose electrons is due to their relatively low electronegativity and low ionization energy. Electronegativity is a measure of an atom’s ability to attract electrons, while ionization energy is the amount of energy required to remove an electron from an atom. Since metals have lower values for both these properties compared to non-metals, they readily give up their electrons.
For example, sodium (Na), a common metal, has one electron in its outermost shell. By losing this electron, sodium becomes a sodium ion (Na+), which has a full outer shell and is therefore more stable. This process is central to the formation of ionic compounds, where metal cations pair with non-metal anions to create stable structures.