Why is it that a number of smaples with the same formula, C8H18 can have different properties?

Answer 1

Because there are different spatial arrangements, or isomers, of that molecule. You can have n-octane, 2-methylheptane, 3-methylheptane, 4-methylheptane, 2,3-dimethylhexane, etc. Those molecules, having different shapes and thus different intermolecular forces, will have different chemical and physical properties, all based on their structures.

Answer 2

the compounds have the same number of each atom but the arrangement and or the structure is different giving them different functions

Answer 3

It depends on how the molecules are arranged.