Coulomb's law is a complex but a very useful relationship encountered in introductory general chemistry. In its mathematical form it may be expressed as,

F = (k.Q⁺ .Q^-)/R²

where F is force of attraction between two oppositely charged species (Qs), k is a proportionality constant and R is the distance between the charged particles.

The sizes of atoms and ions are dependent on the force of attraction between the valence electrons and the nucleus. None of the popular textbooks presents an explanation of trends in sizes based on Coulomb's law. A life experience that parallels the law and a simple application Coulomb's law to explain trends in sizes among members of periodic groups and rows will be presented.