Nowadays, scientists believe all particles are made from just two types of particle, known as quarks and leptons. Molecules Atoms join together to form molecules. Hydrogen atoms, for instance, usually exist only in pairs, or joined with atoms of other elements. Compounds are made of identical molecules, each with the same combination of atoms. The atoms in a molecule are held together by bonds.
Bonds are the forces that exist between atoms and are generated by electrons.
The strength and form of these bonds varies. In diamond, which is pure carbon, five carbon atoms are linked together in a pyramid or tetrahedron shape so strong that diamond is one of the hardest substances in the world. Carbon joins up with other atoms so well that a single molecule of some carbon compounds such as DNA can be made from millions of atoms. There are so many kinds of molecules containing carbon that an entire area of chemistry is devoted to studying them. It is called organic chemistry, because molecules containing carbon are the basis of life.