Step 1 - Understanding the general molecular formula for an alkane
All akanes can be reduced to a general formula that relates the number of H atoms to the number of C atoms. This general formula is:
[tex]C_nH_{2n+2}[/tex]What this formula means is that, if the number of C atoms in the alkane is n, then the number of H atoms will be 2n+2. This is a fixed relation and we can use it to discover the molecular formula for any alkane.
Step 2 - Applying the formula for 7, 8, 9 and 10 C
Since we have a formula relating the number of H to the number of C, we just need to substitute n for the number of C in each case:
[tex]\begin{gathered} n=7,2n+2=16\rightarrow C_7H_{16} \\ \\ n=8,2n+2=18\rightarrow C_8H_{18} \\ \\ n=9,2n+2=20\rightarrow C_9H_{20} \\ \\ n=10,2n+2=22\rightarrow C_{10}H_{22} \end{gathered}[/tex]
