Atomic Structure

Atoms are made up of a nucleus comprising protons and neutrons, encircled by electrons in shells. The number of subatomic particles in an atom can be determined from the atom`s atomic number and mass number.

Subatomic Particles

The nuclei of the entire atoms include subatomic particles called protons. The nuclei of most atoms also contain neutrons.

The mass of an electron is so tiny in comparison to a proton or a neutron. As the nucleus includes protons and neutrons, much of the mass of an atom is focused on its nucleus.

The proton has a positive charge (+1),

The electron has a negative change (-1),

The neutron has no charge (0).

Atomic Number and Mass Number

Atomic number is the number of protons in an atom.

An atom holds equal amounts of protons and electrons. As protons and electrons have equal and opposite charges, this implies that the overall electrical charge of an atom is zero.

Mass Number is the total number of protons and neutrons of an atom.

Isotopes

Isotopes are atoms that have the same number of protons but different number of neutrons. They have the same atomic number but different mass numbers.