Butane nomenclature

The general formula of alkanes is CnH2n+2. Alkanes are saturated hydrocarbons, so each carbon has four single bonds. Then you draw the main chain and fill the single bond of carbon with H.

As for how the general formula comes from, it is also the above reason: assuming that there is no branch, each C in the middle of the chain segment is connected with two C's, so the remaining two bonds can be connected by hydrogen, and the C's at both ends are only connected with 1 C's, so three H's can be connected, so the chain of n C's is divided into two at both ends and n-2 in the middle, totaling * * * 2 * 3+2 *.