A molecule is made up of ATOMS, which are the smallest units of matter. Molecule makeup refers to the arrangement of ATOMS that make up a molecule. The ATOMS in a molecule are held together by chemical bonds, which can be either covalent or ionic. Covalent bonds involve the sharing of electrons between two ATOMS, while ionic bonds involve the transfer of electrons from one atom to another. The arrangement of ATOMS in a molecule determines its properties, such as its shape, size, and reactivity.