[Elisheva2000]

I'm having difficulty telling isomers from one another. When I draw all the isomers for a certain molecular formula I find out that many of them are the same, only flipped around.

Can anyone offer a method to identify identical isomers?

[plu]

A good way to identify identical isomers is to try to name them.  If the two structures have the same name, they're identical!  For simple molecular formulas, this is usually the best thing to do.  However, if you are dealing with larger molecules, a good idea would be to try to draw the isomers systematically - i.e.  start with the longest carbon chains and work your way down.

[Lexus74]

There is a formula to find out how many isomers there can be, i cant remember it now.
Otherwise, you just have to find as many as you can. There is no way to tell if you have them all unless its a relativily small molecule.

[plu]

I don't believe there is a formula for finding the number of isomers possible given a chemical formula (you just have to try to find them all  ).  There is however a formula for finding the maximum number of stereoisomers, given the number of stereocentres in a molecule.  # of stereoisomers = 2^{# of stereocentres}