What are the structural differences between the nine possible isomers of heptane (C7H16) ?

Heptane has nine structural isomers are 2-methylhexane, 3-methylhexane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 3,3-dimethylpentane, 3-ethylpentane and 2,2,3-trimethylbutane. Each compound must have the same molecular formula but the structure of each are different from each other.