An ion is an atom or molecule that has gained or lost one or more electrons, giving it an electric charge. Think of an atom like a balanced team with equal players on each side. When it loses an electron (which carries a negative charge), it becomes positively charged. When it gains an electron, it becomes negatively charged. Either way, it's now an ion.

Ions matter because opposite charges attract. Positive ions pull toward negative ions, and this attraction holds many substances together. Table salt, for example, is made of positive sodium ions bonded to negative chloride ions. When you dissolve salt in water, these ions separate and can conduct electricity.

Your body depends on ions constantly. Sodium and potassium ions help your nerves send signals and your muscles contract. Without the right balance of ions, your heart couldn't beat properly.

Scientists can create ions by adding energy to atoms and knocking electrons loose. Lightning produces ions in the air, which is why the atmosphere can feel different after a thunderstorm.