Oxygen: Difference between revisions
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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 (CO<sub>2</sub>). | 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 (CO<sub>2</sub>). | ||
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<sup>th</sup> 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. | 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<sup>th</sup> 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. | ||
==Chemical properties== | |||
The oxygen atom in its quantum mechanical ground state is a [[electron-spin]] triplet (''S'' = 1), and has [[orbital angular momentum]] quantum number ''L'' = 1; the ground state atom is in a <sup>3</sup>''P'' state with electron configuration 1''s''<sup>2</sup>2''s''<sup>2</sup>2''p''<sup>4</sup>. The O<sub>2</sub> molecule in its ground state has the electron configuration | |||
1σ<sup>2</sup><sub>''g''</sub> | |||
1σ<sup>2</sup><sub>''u''</sub> | |||
2σ<sup>2</sup><sub>''g''</sub> | |||
2σ<sup>2</sup><sub>''u''</sub> | |||
1π<sup>4</sup><sub>''u''</sub> | |||
3σ<sup>2</sup><sub>''g''</sub> | |||
1π<sup>2</sup><sub>''g''</sub>. | |||
The molecular orbitals 1π<sub>''g,x''</sub> and 1π<sub>''g,y''</sub> are singly occupied and couple to a triplet spin. Hence the O<sub>2</sub> molecule is a spin triplet in its ground state and is therefore [[paramagnetic]]. | |||
Revision as of 03:52, 14 September 2007
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 18th 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.
Chemical properties
The oxygen atom in its quantum mechanical ground state is a electron-spin triplet (S = 1), and has orbital angular momentum quantum number L = 1; the ground state atom is in a 3P state with electron configuration 1s22s22p4. The O2 molecule in its ground state has the electron configuration 1σ2g 1σ2u 2σ2g 2σ2u 1π4u 3σ2g 1π2g. The molecular orbitals 1πg,x and 1πg,y are singly occupied and couple to a triplet spin. Hence the O2 molecule is a spin triplet in its ground state and is therefore paramagnetic.