* The same molecular formula: All isomers of pentane will have the chemical formula C5H12.

* The same number of carbon atoms: They will all have five carbon atoms.

* The same number of hydrogen atoms: They will all have twelve hydrogen atoms.

However, isomers of pentane will differ in their connectivity, meaning the way the carbon atoms are bonded to each other. This difference in structure leads to different physical and chemical properties for each isomer.