How are ionic compounds formed?

Ionic compounds are formed by the transfer of electrons from one atom to another. This typically occurs between metals and non-metals. In this process, metals tend to lose electrons and become positively charged ions, while non-metals gain those electrons and become negatively charged ions. The electrostatic attraction between these oppositely charged ions leads to the formation of a stable ionic compound.

This transfer of electrons creates ions that are crucial for the formation of ionic bonds. For example, when sodium (a metal) reacts with chlorine (a non-metal), sodium loses an electron to become Na⁺, while chlorine gains that electron to become Cl⁻. These ions then attract each other, resulting in the formation of sodium chloride, or table salt.

The other options describe different processes. Sharing electrons defines covalent bonding, which occurs between non-metal atoms. Solidifying gases pertains to phase changes rather than chemical bonding. Fusing atoms together generally refers to nuclear fusion, which is unrelated to the formation of chemical compounds. Thus, the transfer of electrons is the fundamental mechanism behind the formation of ionic compounds.