Ionize means to give an atom or molecule an electrical charge by adding or removing electrons. When something ionizes, it transforms from being electrically neutral into a particle called an ion that carries either a positive or negative charge.

This happens constantly in the world around you. When lightning flashes through the sky, it ionizes the air molecules along its path, creating that sharp smell you sometimes notice after a thunderstorm. The sun's radiation ionizes gases in the upper atmosphere, creating brilliant auroras near the North and South Poles. Inside your body, salt dissolves in water and ionizes into separate sodium and chloride ions that help your nerves send signals and your muscles contract.

Scientists use machines called particle accelerators to ionize atoms for research. Smoke detectors ionize air to detect smoke particles. Even the glow-in-the-dark plasma ball you might see at a science museum works by ionizing gas inside a glass sphere.

Understanding how atoms ionize has helped scientists figure out how batteries work, how our nervous system functions, and how stars produce light.