 Hydrogen forms a vast array of compounds with carbon called the hydrocarbons , and an even vaster array with heteroatoms that , because of their general association with living things , are called organic compounds . The study of their properties is known as organic chemistry and their study in the context of living organisms is known as biochemistry . By some definitions , " organic " compounds are only required to contain carbon . However , most of them also contain hydrogen , and because it is the carbon @-@ hydrogen bond which gives this class of compounds most of its particular chemical characteristics , carbon @-@ hydrogen bonds are required in some definitions of the word " organic " in chemistry . Millions of hydrocarbons are known , and they are usually formed by complicated synthetic pathways that seldom involve elementary hydrogen . 
