Carbon

Carbon is a group 14 element and can make up to four covalent bonds with four atoms and is a versatile element that can form many shapes. Carbon molecules form the basis of life on Earth—all living matter is based on carbon molecules.

Carbon can bond to other carbon atoms and form long carbon chains. These carbon-carbon bonds are strong. Due to carbon's ability to form many different carbon-carbon bonds, there are a wide variety of carbon molecules. There is an entire field of study called organic chemistry that focuses on the study of carbon-containing molecules. Carbon atoms are also an essential component of fossil fuels, like coal.

The simplest organic compounds are made up of carbon and hydrogen atoms. An example of this is methane (CH4). Ethane (C2H6) contains two carbon atoms, six hydrogen atoms, one carbon-carbon bond and six carbon-hydrogen bonds. Carbon atoms can form single, double, or triple bonds with one another. Ethene (C2H4) has one carbon-carbon double bond, and ethyne (C2H2) has a carbon-carbon triple bond.
Hydrogenation is a reaction in which hydrogen is added to a compound. For instance, the process could involve a chemical reaction where two hydrogen atoms are added across a carbon double bond, creating a molecule with a carbon-carbon single bond and an additional hydrogen attached to each carbon. One example of a hydrogenation reaction is converting ethyne into ethene.
${{\rm{C}}_2}{{\rm{H}}_2}\!\left( g \right) + {{\rm{H}}_2}\!\left( g \right) \rightarrow {{\rm{C}}_2}{{\rm{H}}_4}\!\left( g \right)$
In this reaction, two hydrogen atoms are added to the carbons bearing the triple bond, resulting in the reduction of the triple bond to a double bond.