Question

Why an atom becomes negatively charge when it gains one or more?

Answer 1

All atoms have a balanced charge, with an equal number of electrons (negative charge) and protons (positive charge).

Thus if a given atom loses an electron, it loses net negative charge and becomes a positively charged ion. If a given atom loses a proton, it loses net positive charge and becomes a negatively charged ion.

These are known as cations (positive charge) and anions (negative charge).

Hope it helps!!