Why Does 3-Methylheptane Have 18 Hydrogens Instead of 16?

[tica86]

So I am given 3-methylheptane I know that it looks like this:


CH3-CH2-CH-CH2-CH2-CH2-CH3
And the methyl group is attached to CH

It is heptane so I have 7 carbons and a total of 15 Hydrogens but I don't understand why it isn't 16 Hydrogens don't I use the formula
CnH2n+2=16Hydrogen
If I don't use the formula then how do I determine the number of Hydrogens?

Can someone please explain, I don't understand why one of it's Hydrogen is replaced with methyl, thanks!

 

[Tsar_183]

3-Methylheptane actually contains 8 carbons, not seven (Remember the naming, it is heptane (7 carbons), plus a methy group (on the 3rd carbon) is a -CH3 group). Thus, using your formula C_nH_2n+2, you should have C8H18, not C7H16 or C8H16. :)

By the way, the structural skeleton form is: CH3-CH2-CH(CH3)-CH2-CH2-CH2-CH3