Carboxylic acids are another family of compounds made of carbon, hydrogen and oxygen. Each molecule ends in the -COOH group. The first four members are methanoic acid, ethanoic acid, propanoic acid and butanoic acid, with one, two, three and four carbon atoms.
Their formulae are HCOOH, CH3COOH, C2H5COOH and C3H7COOH. The carbon in the -COOH group counts towards the total, so in butanoic acid only one of the four carbon atoms is in the -COOH group and the other three form the chain.
To draw one showing all the covalent bonds, start with the -COOH carbon. It forms a double bond to one oxygen atom and a single bond to a second oxygen atom. That second oxygen atom is joined to a hydrogen atom, making an -OH. The fourth bond of the carbon goes to the rest of the chain, or to a hydrogen atom in methanoic acid.
