OXYGEN

CHALCOGENS ELEMENT

Atomic number:	8
Group numbers:	16
Period:	2
Electronic configuration:	[He] 2s² 2p⁴
Formal oxidation number:	-2
Electronegativities:	3.44
Atomic radius / pm:	60.4
Relative atomic mass:	[15.999 03, 15.999 77]

Oxygen was discovered by Carl William Scheele (SE) in 1772. The origin of the name comes from the Greek words oxy genes meaning acid and forming (acid former). It is a colourless, odourless gas; pale blue liquid. Oxygen is extremely reactive and forms oxides with nearly all other elements except noble gases. It is the most abundant element in the earth's crust and makes up almost 21% of the atmosphere. Oxygen is obtained primarily from liquid air by fractional distillation. Small amounts are made in the laboratory by electrolysis of water. Oxygen is used in steel making, welding and supporting life. Naturally occurring ozone (O3) in the upper atmosphere shields the earth from ultraviolet radiation. The price of 99.99 % pure oxygen gas costs 188.90 €/dm3 in small quantities (1 dm3) and about 1.46 €/dm3 in large quantities (300 dm3).

PHYSICAL PROPERTIES
Density / g dm^-3:	2000	(solid, m.p.)
	1140	(b.p.)
	1.429	(gas, 273 K)
Molar volume / cm³mol^-1:	8.00	(solid, m.p.)
	14.03	(b.p.)
	22392.44	(gas, 273 K)
Electrical resistivity / µΩcm:	-	(20 °C)

THERMAL PROPERTIES
Thermal conductivity / W m^-1K^-1:	0.0263
Melting point / °C:	-218.7916
Boiling point / °C:	-182.95
Heat of fusion / kJ mol^-1:	0.444
Heat of vaporization / kJ mol^-1:	6.82
Heat of atomization / kJ mol^-1:	246.785

IONIZATION ENERGIES
First ionization energy / kJ mol^-1:	1313.95
Second ionization energy / kJ mol^-1:	3388.33
Third ionization energy / kJ mol^-1:	5300.51

ABUNDANCE OF ELEMENT
in the atmosphere / ppm:	209500
in the Earth's crust / ppm:	466000
in the oceans / ppm:	(H2O)

CRYSTALLOGRAPHIC DATA
Crystal structure:	simple cubic
Unit-cell dimensions / pm:	a=683
Space group:	Pm3n

ISOTOPES
Isotope	Relative atomic mass	Mass percent (%)
¹⁶O	15.994914622(2)	99.762(15)
¹⁷O	16.9991315(2)	0.038(3)
¹⁸O	17.9991604(9)	0.200(12)

REDUCTION POTENTIALS
Balanced half-reaction	E^o / V
O₂(g) + 4H⁺ + 4e^- → 2H₂O	+1.229
O₂(g) + 4H⁺ + 4e^- → 2H₂O	+0.815	([H⁺] = 10^-7 mol dm^-3)
O₂(g) + 2H₂O + 4e^- → 4OH^-	+0.401
O₂(g) + H₂O + 2e^- → HO₂^- + OH^-	+0.076
O₂(g) + 2H⁺ + 2e^- → H₂O₂	+0.682
O₃(g) + 2H⁺ + 2e^- → O₂(g) + H₂O	+2.07
O₃(g) + 6H⁺ + 6e^- → 3H₂O	+1.501
O₃(g) + H₂O + 2e^- → O₂(g) + 2OH^-	+1.24
HO₂^- + H₂O + 2e^- → 3OH^-	+0.88
H₂O₂ + 2H⁺ + 2e^- → 2H₂O	+1.776