Isomerism

Structural isomerism:
exitst when molecules are composed of the same number & type of atoms but these atoms are arranged in different ways.

Stereoisomerism:
the atoms making up the isomers are joined up in the same order but have different arrangement in space. 

Chain Isomerism:
The C skeletal can be rearranged differently, either as a straight chain or as a branched chain in different ways.
These ismoers ahve similar chemical properties but different physical properties because of the change in shape of the molecule.

The skeleton & functional gropu can be the same, but the group could be attached to a different carbon atom.
This leads to different chemical & physical properties. 

The same atoms can be arranged into different functional groups, this leads to a difference in chemical properties.

There must be a C=C (double bond) and each carbon must be attached to 2 different groups.