* Protons: Positively charged particles in the nucleus of an atom.

* Electrons: Negatively charged particles that orbit the nucleus.

* Neutral Atom: In a neutral atom, the number of protons (positive charges) equals the number of electrons (negative charges), resulting in a net charge of zero.

When an atom gains an extra electron, it gains a negative charge. This is because the number of negatively charged electrons now outweighs the number of positively charged protons.

For example, a sodium atom (Na) normally has 11 protons and 11 electrons. If it gains an extra electron, it becomes a sodium ion (Na-) with a charge of -1.