What is the difference between an alkane and and alkene

An alkane is a chain of carbons connected together by single bonds (-C-C-C-C-C-). All carbons have to have 4 bonds, so the carbons in the middle of the chain are attached to two other carbons, and two other atoms (e.g. hydrogens). The carbons on the end of the chain are only attached to one other carbon, and so they have three hydrogens. In an alkene carbon chain, two of the carbons are linked together by a double bond, this counts as two single bonds. (-C-C=C-C-). The carbons must still have 4 bonds, and so any missing bonds must be used to attach to other atoms e.g. hydrogen.