Oxygen

Oxygen (chemical symbol O) is the most abundant (46.6%) chemical element of the lithosphere (the earth crust). It is a constituent of water (H₂O), of rocks and sand in the form of silicium oxide (SiO₂) and part of the atmosphere (21%) in the form of the oxygen molecule (O₂). The O-atom has nuclear charge 8 e, where e is the elementary charge, and 8 electrons, which means that it occupies the eighth position in the Periodic system of elements. Atomic oxygen is very reactive, so that the element does not occur naturally in free form, but only in compounds.

History

We now know that the burning of wood and other fuels is a process of oxidation. It is a chemical reaction of fuel with atmospheric oxygen, yielding mainly heat and carbondioxide (CO₂). Although this chemical reaction was the most important discovery in the history of mankind, for many centuries burning, flames, and fire were not at all understood. The first step in understanding came in the early 18^th century when Georg Ernest Stahl conjectured that in the burning process a substance called phlogiston escapes from the flames. This idea was adopted by many chemists, among whom the independent discoverers of oxygen Carl Wilhelm Scheele (in 1771) and Joseph Priestly (in 1774). They discovered what they called dephlogisticated air. Soon after (1777) Antoine Laurent Lavoisier communicated to the French Academy that dephlogisticated air is a constituent of several acids and hence must be a chemical element. Because Lavoisier believed (erroneously) that the presence of oxygen in an acid was essential, he proposed to replace the name by oxygen (generation of acidity, the old Greek word for wine vinegar being oxys—όξύς, from the Greek word for sharp, also όξύς). He understood that oxygen was an important part of air, and this was made undoubtedly clear when oxygen was separated by distillation from liquid air in 1883.