Oxygen [O]

A. Characteristic

An : 8

N : 8

Am : 15.9994 (3) g/mol

Group No : 16

Group Name : Chalcogen

Block : p-block

Period : 2

State : gas at 298 K

Colour : colourless as a gas, liquid is pale blue

Classification : Non-metallic

Boiling Point : 90.20K (-182.95^oC)

Melting Point : 54.36K (-218.79^oC)

Density : 1.429g/l

B. Discovery Information

Who : Joseph Priestley, Karl Wilhelm Scheele

When : 1774

Where : England/Sweden

C. Name Origin

Greek : oxus (acid) and gennan (generate). "Oxygen" in different languages.

D. Sources

Obtained primarily from by liquification and then fractional distillation of the air. World wide production is around 100 million tons.

E. Abundance

Universe : 10000 ppm

Sun : 9000 ppm

Atmosphere : 2.095 x 10⁵ ppm

Earth’s Crust : 4.74 x 10⁵ ppm

Human : 6.1 x 10⁸ ppb by weight; 2.4 x 10⁸ ppb by atoms

F. Uses

Used in steel making, production of methanol (CH₃OH), welding, water purification, cement and rocket propulsion. It is also required for supporting life and combustion. Oxygen is a major component of air, produced by plants during photosynthesis, and is necessary for aerobic respiration in animals.

G. Notes

Liquid and solid O₂ are both a light blue colour. Ozone (O₃) is a deeper blue colour. Oxygen is the second most common element on Earth, composing around 46% of the mass of Earth’s crust and 28% of the mass of Earth as a whole, and is the third most common element in the universe. Forms almost 21% of atmosphere.

H. Hazards

Certain derivatives of oxygen, such as ozone (O₃), singlet oxygen, hydrogen peroxide (H₂O₂), hydroxyl radicals and superoxide (O^2-), are highly toxic. Highly concentrated sources of oxygen promote rapid combustion and therefore are fire and explosion hazards in the presence of fuels.

I. Allotropes of Oxygen

1. Dioxygen [ O₂ ]

A gas at room temperature. Dioxygen exists as a diradical (contains two unpaired electrons) and is the only allotrope of any element with unpaired electrons.

2. Ozone [ O₃ ]

Ozone was discovered by Christian Friedrich Schonbein in 1840, who named it after the Greek word for smell (ozein), from the peculiar odour in lightning storms. The actual odour from a lightning strike is from electron that have been freed during the rapid chemical changes that take place, and not ozone.

Ozone is a pale blue gas at standard temperature and pressure. It forms a dark blue liquid below -112^oC and a dark blue solid below -193^oC. Ozone is a powerful oxidizing agent. It is also unstable, decaying to ordinary oxygen (O₂). It is present in low concentrations throughout the Earth’s atmosphere: ground level ozone is an air pollutant with harmful effects on lung function and in the upper atmosphere it prevents damaging ultraviolet light from reaching the Earth’s surface.

It is also formed from O₂ by electrical discharges such as lightning, and by action of high energy electromagnetic radiation.

Some kinds of electrical equipment generate significant levels of ozone. This is especially true of devices using high voltages, such as television sets, laser printers, and photocopiers. Ozone is widely used in disenfecting water, killing bacteria and cleaning and bleaching fabrics.

3. Tetraoxygen [ O₄ ]

The most recently discovered allotrope of oxygen. It is a deep red solid and is created by pressurizing O₂ to the order of 20 GPa. Its properties are being studied for use in rocket fuels and similar applications, as it is a much more powerful oxidizer than either O₂ or O₃.

J. Reactions of Oxygen

Oxygen does not react with acids or bases under normal conditions.

1. Reactions with water

Oxygen will not react with water.

2. Reactions with air

Oxygen gas does not react with itself or nitrogen under normal conditions. However the effect of ultraviolet light upon oxygen gas is to form the blue gas ozone, O3.

3. Reactions with halogens

Irradiation of a low pressure mixture of oxygen and fluorine gases will produce dioxygen difluoride.

O_2(g) + F_2(g) --> F₂O_2(g)

K. Isotopes of Oxygen

¹⁶O [8 neutrons]

Abundance: 99.762

Stable with 8 neutrons

¹⁷O [9 neutrons]

Abundance: 0.038%

Stable with 9 neutrons

¹⁸O [10 neutrons]

Abundance: 0.205%

Stable with 10 neutrons