(1) Those compounds should be abundant on a planet, but pure oxygen, whether monatomic or molecular, should be vanishingly scarce - as it is, in fact, on Mars and Venus.(2) For example, aluminum, helium, and sodium are monatomic elements, or elements whose atoms can exist alone, without forming molecules.(3) Data for monatomic gases like argon and helium give exact agreement, and many diatomic gases show experimental results in close accord with the theory.(4) Although the most common anion formed by oxygen is monatomic , oxygen can also form diatomic ions known as peroxides and superoxides (monovalent).(5) Dalton had used Ockham's Razor to assume elemental gases were monatomic .
