Joseph Priestley and Carl Wilhelm Scheele both independently discovered oxygen, but Priestly is usually given credit for the discovery. They were both able to produce oxygen by heating mercuric oxide (HgO). Priestley called the gas produced in his experiments 'dephlogisticated air' and Scheele called his 'fire air'.
Daniel Rutherford originally discovered Nitrogen in 1772, hydrogen was discovered by Henry Cavendish in 1672 and oxygen was discovered by Joseph Priestly, Antoine Lavoisier, and Carl Wilhelm Scheele.
