what is an example of an element containing a double bond
Look at the number of bonding domains. for example, Calcium has a charge of +2 and oxygen has a charge of -2. They bond, and calcium gives up 2 electrons to the same oxygen, creating a double bond, forming a binary compound (Calcium Oxide) It all depends on the elements. The main thing is the number of electrons being transfered.
Your first step should be to analyse the compound. For example, if the compound is carbon, you know it always has a valence of four, so, if it has a formula C2H4 (ethylene) it obviously has a double bond. There are difficulties here because benzene C6H6 can be considered to have 6 1.5 C-C bonds, being aromatic.