Atom

* The smallest particle of an element that has the properties of the element

Electron

* A negatively charged particle in an atom that occupies energy levels around the nucleus

Molecule

* Two or more atoms of the same element or of 2 different elements bound together by covalent bonds

(A covalent bond, also called a molecular bond, is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs, and the stable balance of attractive and repulsive forces between atoms, when they share electrons, is known as covalent bonding)

Neutron

* A neutron particle in the nucleus of an atom

Nucleus

* The positively charge center of an atom made up of protons and neutrons, except hydrogen which has only a proton in its nucleus

Proton

* A positively charged particle in the nucleus of an atom