What is the difference between alkyl halide and alkene
An alkyl is when one (or more) of these spaces is taken up with something other than a hydrogen. So an alkyl halide is when that space is taken up by a halogen instead of a hydrogen.
Alkenes are unsaturated hydrocarbons that have a minimum of one carbon-carbon double bond. The general formula for an alkene is CnH2n. There will be no foreign Components like halogen, nitrogen and etc.