Define the molecular formula of a compound as the number and type of different atoms in one molecule

Define structural isomers as compounds with the same molecular formula, but different structural formulae, including (C_4H_{10}) as (CH_3CH_2CH_2CH_3) and (CH_3CH(CH_3)_2CH_3) and (C_4H_8) as (CH_3CH_2CH=CH_2) and (CH_3CH=CHCH_3)