Both alkanes and alkenes are hydrocarbons, which means they only contain carbon and hydrogen atoms.
Alkanes are saturated hydrocarbons, which means each carbon atom is bonded to four other atoms and there are no double bonds in the molecule. The formula of the molecule will be CnH2n
Alkenes are unsaturated hydrocarbons, which means there are one or more double bonds between carbons atoms within the molecule. The formula of the molecule will be CnHn