Alkenes have a general formula of CnH2n, where "n" may equal any number larger than one. Alkenes are organic compounds that are generally only comprised of hydrogen and carbon atoms. Due to the general structure of alkenes, they always have twice as many hydrogens as carbons.
Alkenes may have single or double bonds. Short-chain alkenes with only two carbons generally are connected via double bonds between the carbon atoms and single bonds between the carbon and hydrogen atoms. Longer-chain alkenes generally have single and double bonds between the chains of carbon atoms and have single bonds between hydrogen and carbon atoms. Hydrogen atoms always have only single bonds because they only have one electron to share, and double bonds require two electrons.