How is the mass of the atom calculated?

by adding the number of protons and electrons

by adding the number of protons and neutrons

by subtracting the number of electrons from the number of protons

by adding the number of neutrons and electrons

Answer: By adding the number of protons and neutrons

Explanation:

Protons and neutrons have very similar masses and are used in calculating the mass of an atom. One would calculate the mass of an atom by doing the (mass of a proton) x (# of protons) + (mass of a neutron) x (# of neutrons). Electrons have such a small mass that their mass is considered negligible and therefore is not included in mass calculations for atoms.

mass of a proton: 1.67262 * 10-27 kg

mass of a neutron: 1.67493*10-27 kg

mass of an electron: 9.10938 * 10-31 kg