Atoms are the smallest units of matter that retain chemical properties.

Atoms consist of protons, neutrons, and electrons.

Protons have a positive charge, electrons have a negative charge.

Neutrons have no charge and add mass to the atom.

The number of protons defines the element (atomic number).

Electrons orbit the nucleus in energy levels or shells.

Isotopes are atoms of the same element with different numbers of neutrons.

Most of the atom’s mass is in the nucleus.

Atoms combine to form molecules through chemical bonds.

Atoms are mostly empty space.