Draw an Alkane with the molecular formula C4H8 as well as a possible functional group isomer and state a chemical test you can use to differentiate between the two.

Many organic molecules follow specific formulas to help identify them. For Alkanes this is: C_nH_2n+2 (n being the total number of carbon atoms). However, this is not the case with the given molecular formula and so it is useful here to remember that the number of covalent bonds an atom has is often equivalent to 18 - x (where x is the number of the group to which the element in question belongs). For Carbon this comes to 18 - 14 = 4 bonds. Using this information we can go about drawing the molecule as usual and since there are 2 carbons that don’t have four bonds as a chain alkane we bond these carbons together to give Cyclobutane.   Functional group isomers refer to compounds with the same molecular formula but different functional groups that change the molecules chemistry. It is an example of structural isomerism. In this case given the formula we can deduce the isomer to be an Alkene. These are differentiated from Alkanes using Bromine which Alkenes attack to form Halo-Alkanes thereby decolourising bromine from brownish-orange to colourless.