In its elemental form, carbon takes different forms. Carbon can exist in crystalline forms such as graphite and diamond, which have very different characteristics. Diamonds are the hardest substances on Earth, whereas graphite is soft.
Hydrogen and carbon combine with each other and other elements to form a class of compounds called organic compounds, which are important to living things. Carbon has four valence electrons, each of which can be shared with another element. The element commonly sharing an electron with carbon is hydrogen. A single carbon atom can bond with four hydrogen atoms. In this way, carbon can form long chains. Fats, proteins, carbohydrates and nucleic acids are organic compounds made with long, carbon backbones.Learn more about Chemistry