Zinc: the essentials
Zinc-deficient animals require 50% more food to gain the same weight of an animal supplied with adequate amounts of zinc. Zinc is not particularly toxic and is an essential element in the growth of all animals and plants.
Plating thin layers of zinc on to iron or steel is known as galvanising and helps to protect the iron from corrosion.
Zinc is a bluish-white, lustrous metal. It is brittle at ambient temperatures but is malleable at 100 to 150°C. It is a reasonable conductor of electricity, and burns in air at high red heat with evolution of white clouds of the oxide.
The picture above shows the result from burning a mixture of zinc metal powder and sulphur (only to be demonstrated by a professionally qualified chemist).
Zinc: historical information
Centuries before zinc was recognized as a distinct element, zinc ores were used for making brass (a mixture of copper and zinc). A brass dating from between 1400-1000 BC has been found in Palestine. An alloy containing 87% zinc was found in prehistoric ruins in Transylvania. The smelting of zinc ores with copper was apparently discovered in Cyprus and was used later by the Romans. Metallic zinc was produced in the 13th century in India by reducing calamine (zinc carbonate, ZnCO3) with organic substances such as wool.
The metal was rediscovered later in Europe. William Champion set up a zinc industry in Bristol (England) in the 1740s. Other plants were established a little later in Belgium and Silesia.
Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions). This was further evidence for atoms. Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. The symbol used by Dalton for zinc is shown below. [See History of Chemistry, Sir Edward Thorpe, volume 1, Watts & Co, London, 1914.]
Zinc around us Read more »
Zinc is essential in the diets of plants and animals. Zinc shortage in soils around the world is an important problem. Zinc is the key component of many enzymes. The protein hormone insulin contains zinc.
Zinc plays a role in reproduction and also sexual maturation. Zinc deficiency resluts in stunted growth and in male sexual immaturity. This is reversed on the addition of zinc in the diet. Some organisms seem to accumulate zinc.
Zinc is never found as the free metal but there are a number of important ores such as sphalerite (zincblende, zinc sulphide, ZnS), smithsonite (zinc carbonate, ZnCO3), zincspar (also zinc carbonate, ZnCO3), and marmatite (zinc sulphide, ZnS, containing some iron sulphide, FeS). Zinc is wide spread around the world. Important deposits are located in North America and Australia.
|Location||ppb by weight||ppb by atoms||Links|
|Human||33000 ppb by weight||3200 atoms relative to C = 1000000|
Physical properties Read more »
Heat properties Read more »
- Melting point: 692.68 [419.53 °C (787.15 °F)] K
- Boiling point: 1180 [907 °C (1665 °F)] K
- Enthalpy of fusion: 7.35 kJ mol-1
Crystal structure Read more »
The solid state structure of zinc is: hcp (hexagonal close-packed).
Zinc: orbital properties Read more »
Zinc atoms have 30 electrons and the shell structure is 18.104.22.168. The ground state electronic configuration of neutral Zinc is [Ar].3d10.4s2 and the term symbol of Zinc is 1S0.
- Pauling electronegativity: 1.65 (Pauling units)
- First ionisation energy: 906.4 kJ mol‑1
- Second ionisation energy: 1733.3 kJ mol‑1
Isolation: zinc metal is readily available commercially so it is not normally necesary to make it in the laboratory. Most zinc production is based upon sulphide ores. These are roasted in industrial plants to form zinc oxide, ZnO. This may be reduced with carbon to form zinc metal, but in practice ingenious technology is required to ensure that the resulting zinc does not contain oxide impurities.
ZnO + C → Zn + CO
ZnO + CO → Zn + CO2
CO2 + C → 2CO
The other type of extraction is electrolytic. Dissolution of crude zinc oxide, ZnO, in sulphuric acid gives zinc sulphate, ZnSO4 in solution. Cadmium is an impurity and this is removed as a precipitate of cadmium sulphate by the addition of zinc dust. Electrolysis of the ZnSO4 solution using aluminium cathodes and lead alloyed with silver anodes gives pure zinc metal coated on the aluminium. Oxygen gas is liberated at the anode.
Very pure zinc may be formed from crude zinc by zone refining and single crystals can be grown with purities of better than 99.9999%.
Zinc isotopes Read more »
Zinc isotopes are used extensively in both industrial and medical applications. Depleted Zn-64 is added to the cooling water of nuclear reactors in the form of oxide or acetate to prevent stress corrosion cracking. It also reduces the release of (stable) Co-59 into the cooling water by forming a thin spinel layer on the Co containing steel surfaces. Neutron irradiation of Co-59 will result in the formation of Co-60, a radioisotope which emits high energy gamma radiation and is a major contributor to the dose rate of personnel working in the reactor. Enriched Zn-67 is often used in biological research into the uptake of Zn in the human body. It can also be used for the production of radioactive Ga-67 in smaller cyclotrons. However, by far most Ga-67 is made from Zn-68. Zn-67, Zn-68 and Zn-70 can all be used for the production of the therapeutic isotope Cu-67. Zn-66 has been proposed as an alternative target for the production of Cu-64 and Ga-67. Finally Zn-70 is also used in biological research and in research into super-heavy elements.
|64Zn||63.9291448 (19)||48.63 (60)||0|
|66Zn||65.9260347 (17)||27.90 (27)||0|
|67Zn||66.9271291 (17)||4.10 (13)||5/2||0.875479|
|68Zn||67.9248459 (18)||18.75 (51)||0|
|70Zn||69.925325 (4)||0.62 (3)||0|