Oxygen
On the periodic table, oxygen is the 8th element. It is located in period 2 and group 16. Oxygen is classified into many things. For example, on the periodic table, oxygen is classified as a nonmetal gas with an atomic number of 8 and atomic weight of 15.9994. In addition, it has 6 valence electrons. The symbol of oxygen is O and oxygen has 8 protons, 8 neutrons, and 8 electrons. The electron configuration of oxygen is 1s2, 2s2, 2p4. Oxygen had been produced by several chemists prior to its discovery in 1774, but they failed to recognize it as a distinct element. 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'. The name oxygen was created by Antoine Lavoisier who incorrectly believed that oxygen was necessary to form all acids. Oxygen is the third most abundant element found in the sun, and it plays a part in the carbon-nitrogen cycle, the process once thought to give the sun and stars their energy. Oxygen under excited conditions is responsible for the bright red and yellow-green colors of the Aurora. A gaseous element, oxygen forms 21% of the atmosphere by volume and is obtained by liquefaction and fractional distillation. The atmosphere of Mars contains about 0.15% oxygen. The element and its compounds make up 49.2%, by weight, of the earth's crust. About two thirds of the human body and nine tenths of water is oxygen. The physical state of oxygen is a gas. Physical properties are usually those that can be observed using our senses such as color, luster, freezing point, boiling point, melting point, density, hardness and odor. Oxygen changes from a gas to a liquid at a temperature of -182.96°C (-297.33°F) when it takes on a slightly bluish color liquid. Oxygen can then be solidified or frozen at a