121 Hydrocarbons(碳氢化合物、烃) contain only carbon and hydrogen Hydrocarbons differ from each other by the number of carbon atoms methane CH4 Octane C8H18 polyethylene12.1 Hydrocarbons (碳氢化合物、烃) contain only carbon and hydrogen • Hydrocarbons differ from each other by the number of carbon atoms. methane CH4 Octane C8H18 polyethylene