Alkanes are compounds made of carbon and hydrogen only, so they are hydrocarbons. The first four are methane, ethane, propane and butane. The name starts with meth-, eth-, prop- or but- to show one, two, three or four carbon atoms.
Their formulae are methane CH4, ethane C2H6, propane C3H8 and butane C4H10. They fit the general formula CnH2n+2. For butane, n = 4, so the number of hydrogen atoms is 2 × 4 + 2 = 10.
To draw a molecule showing all covalent bonds, remember that each carbon atom forms four bonds and each hydrogen atom forms one. Each bond is a single line. Methane is one carbon atom with four lines going to four hydrogen atoms. Ethane is two carbon atoms joined by one line, and each carbon atom also has three lines to three hydrogen atoms. Propane has a chain of three carbon atoms and butane a chain of four, with hydrogen atoms added until every carbon atom has four bonds.
