Matter is made of single particles called atoms and is any substance that has either mass or volume. Matter can exist in three states, either as a solid, a liquid or a gas.
Atoms are the basic building blocks of matter and bind together to make elements. Elements are a substance that can only have one type of atom. Hydrogen can only have hydrogen atoms, and oxygen can only contain oxygen atoms.
When two or more atoms combine, they form molecules. Molecules can be comprised of atoms that are different or alike. A water molecule is formed by the combination of two hydrogen atoms and a single oxygen atom. That molecular bond is better known as H2O.
Atoms are made up of three sub-atomic protons called protons, neutrons and electrons. The protons and neutrons are densely packed together in the nucleus, while electrons stay in constant random motion orbiting around the outside of the nucleus. These sub-atomic particles are actually known as composite particles and are made up of smaller particles called elementary particles.
Scientists have identified 37 elementary particles. Photons, bosons, gluons, hadrons, quarks, muons, leptons, taus and neutrinos also constitute parts of an atom. They each play a unique role, such as that of the gluon, which helps to hold quarks in place. Physicists have discovered the Higgs-Boson, which provides mass to the other particles. Other sub-atomic particles are thought to exist, but they have yet to be discovered.