Carbon of interconnecting carbon–carbon bonds, a property that is called catenation. Carbon-carbon bonds are strong and stable. Through catenation, carbon forms a countless number of compounds. A tally of unique compounds shows that more contain carbon that those that do not. A similar claim can be made for hydrogen because most organic compounds also contain hydrogen. The simplest form of an organic molecule is the hydrocarbon—a large family of organic molecules that are composed of hydrogen atoms bonded to a chain of carbon atoms. A hydrocarbon backbone can be substituted by other atoms, known as heteroatoms. Common heteroatoms that appear in
Chemical formula a different connectivity from other molecules that can be formed using the same atoms in the same proportions (isomers). The formula (CH)CH implies a central carbon atom connected to one hydrogen atom and three CH groups. The same number of atoms of each element (10 hydrogens and 4 carbons, or CH) may be used to make a straight chain molecule, "n"-butane: CHCHCHCH. In any given chemical compound, the elements always combine in the same proportion with each other. This is the law of constant composition. The law of constant composition says that, in any particular chemical compound, all samples of