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What is an ion?

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Quick answer

An ion is an atom or molecule that has gained or lost one or more electrons, giving it an electric charge. Losing electrons makes a positive ion; gaining them makes a negative ion. Ions are behind everything from table salt to the electrical signals in your nerves.

Key things to understand

  1. An atom is normally neutral (equal protons and electrons); an ion has lost or gained electrons, so it's charged.
  2. Lose electrons → positive ion (cation); gain electrons → negative ion (anion).
  3. Oppositely charged ions attract and can bond — sodium and chloride ions form table salt (NaCl).
  4. Ions let solutions conduct electricity, which is why salty water conducts.
  5. Your nerves and muscles work by moving ions (sodium, potassium) across cell membranes.

People also ask

How does an atom become an ion?
By gaining or losing electrons. An atom with more electrons than protons is a negative ion; with fewer, it's a positive ion.
What's the difference between a cation and an anion?
A cation is a positively charged ion (it lost electrons); an anion is negatively charged (it gained electrons). Opposite charges attract.
Why does salt water conduct electricity?
Dissolved salt splits into charged ions that move freely, carrying electric current — pure water, with few ions, conducts poorly.