What is an atom or group of atoms with an electric charge called

Ion

Explanation:

An atom is generally neutral, since its number of protons in the nucleus is equal to the number of electrons around the nucleus: since proton and electrons have opposite charge (but equal in magnitude), the total charge of the atom is zero.

However, sometimes atoms can gain or lose electrons: when this happens, they are called ions. In particular:

- When an atom loses one (or more) electrons, it remains with an excess of positive charge, so it is called positive ion

- When an atom gains one (or more) electrons, it remains with an excess of negative charge, so it is called negative ion