The electrical charge of an atom is determined by the number of electrons it has gained/lost. Electrons have a negative charge. We will let "e" be the amount of electrical charge carried by an electron.
If the atom has not lost or gained any electrons, it has a neutral, or zero, charge.
If the atom has 2 extra electrons, the atom is overall negatively charged with a charge equal to -2e.
If the atom has lost 2 electrons, the atom is overall positively charged with a charge equal to +2e.
If you want the charge quantities in Coulombs, use the conversion rate:
e = 1.6×10⁻¹⁹C