Use the drop-down menus to complete the statements.

are pure substances that cannot be broken down into a simpler form.

are units of two or more atoms.

are the smallest possible particles of an element.

are pure substances made of two or more atoms of different elements.

- lead + phosphoric acid = hydrogen + lead(ii) phosphate

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.