OxygenOxygen Atomic number8Atomic weight15.9994Melting point-218.4oC (-361.1oF) Boiling point-183.0oC (-297.4oF) Density (1 atom, 0oC) 1.429 g/lValency2configuration electronic2-6 or 1s22s22p4.Oxygen is one of the most important factors that made the existence of life on this planet possible. Oxygen is also one of the elements that must be present on earth. Oxygen can be found in metals, water and even the subtle oxygen that protects us from the sun's powerful rays. Oxygen is a very unstable element, which makes it easy to create compounds with other elements creating different types of solids and liquids. Oxygen is found in air as O2 and in ozone as O3. Oxygen is essential for life on all planets. The Discovery of Oxygen On August 1, 1774, Joseph Priestly examined the effect of intense heat on mercuric oxide. He noticed that air or gas was easily expelled from the sample. To his surprise, a candle burned with an extraordinarily vigorous flame. He called this new substance deflogistic air according to the current chemical theory of combustion. When he went to Paris in 1775 he showed his discovery to Antoine Lavoisier. When Antoine examined the gas he discovered that deflogistic air combined with metals and other substances. Since some of the compounds form acids, he called the gas Oxygen from the Greek words for acid and I produce. Oxygen in the Atmosphere The atmosphere surrounding the earth is a mechanical mixture of gases. The most important of these gases are oxygen, nitrogen and carbon dioxide. Oxygen is the essential element for life. It is odorless, colorless, tasteless and slightly heavier than air. The main commercial source of oxygen is the atmosphere. Oxygen can be separated from the mixture of gases that make up the atmosphere. This is done by physical means by subjecting the air to very high pressures and low temperatures until it reaches a point where it changes from a gaseous state to a liquid state. Subsequently the liquid is introduced at room temperature, so that the nitrogen, which has a lower boiling point than oxygen, evaporates. Oxygen initially prepared by heating some metal oxides, including mercuric oxide. Ozone Ozone (O3), which takes its name from the Greek word "odor", is a poisonous, colorless and tasteless gas with a characteristic odor. Ozone molecules are likely the source of the odor that can be detected near functioning electrical equipment such as motors and televisions.