What is the molecular formula for methane?

• A. CH4
• B. C2H6
• C. C3H8
• D. C4H10

Answer: (A)

Determining the molecular formula of a simple alkane from its carbon count. Methane is the first member of the alkane family, having one carbon atom. Alkanes follow the formula CnH2n+2, so with n = 1 the hydrogen count is 2(1) + 2 = 4, giving CH4. This also fits the idea that carbon forms four covalent bonds, so one carbon bonded to four hydrogens completes the molecule. The other common alkanes have more carbons (ethane with two carbons and six hydrogens, propane with three and eight, butane with four and ten), which is why their formulas differ. Therefore, the molecular formula for methane is CH4.