What causes atoms to form ions?

Atoms form ions due to the loss or gain of electrons in their outermost shell to achieve a stable electron configuration.

Atoms are the basic units of matter and consist of protons, neutrons, and electrons. The protons and neutrons are located in the nucleus of the atom, while the electrons orbit the nucleus in energy levels, also known as shells. The outermost shell of an atom is called the valence shell. The stability of an atom is determined by the electron configuration in this valence shell.

Atoms strive to achieve a stable electron configuration, which usually means having a full valence shell. This is often referred to as the 'octet rule', as most atoms are most stable when their valence shell is filled with eight electrons. However, not all atoms naturally have a full valence shell. This is where ions come into play.

Ions are atoms that have lost or gained electrons. If an atom loses one or more electrons, it becomes a positively charged ion, or cation. This is because it now has more protons than electrons. On the other hand, if an atom gains one or more electrons, it becomes a negatively charged ion, or anion. This is because it now has more electrons than protons.

The process of losing or gaining electrons is known as ionisation. This usually occurs during chemical reactions, where atoms interact with each other to achieve a stable electron configuration. For example, in the reaction between sodium and chlorine to form sodium chloride, sodium loses an electron to become a sodium ion, while chlorine gains an electron to become a chloride ion. Both ions now have a full valence shell, and are therefore more stable.

In summary, atoms form ions as a way to achieve a stable electron configuration. This involves the loss or gain of electrons in the atom's outermost shell, resulting in a charged particle.