zinc (Zn)

A bluish-white, lustrous, metallic element in group IIB of the periodic table; zinc is an anomalous transition element. It occurs naturally as sphalerite, smithsonite, hemimorphite, and wurtzite, and is extracted by roasting to the oxide and reduction with carbon. Zinc is brittle at room temperatures but malleable when heated. It is used to form a wide variety of alloys including brass, bronze, German silver, various solders, and nickel silver, in galvanizing iron and other metals, for electric fuses, anodes, and meter cases, and in roofing, gutters, and various household objects. Zinc is a vital trace element, occurring in erythrocytes (red blood cells) and insulin.

Compounds of zinc

Chemically zinc is reactive, readily forming divalent ionic salts (Zn²⁺), and zincates (ZnO₂^2-) in alkaline solution; it forms many stable ligand complexes. Zinc chloride is used as a flux, for fireproofing, in dentistry, and in the manufacture of batteries and fungicides. Zinc oxide and sulfide are used as white pigments. Additionally, zinc oxide is an ingredient of many skin preparations that has a mild astringent (dying) action and a soothing effect. Zinc oxide is used to treat painful, itchy, and moist skin (such as eczema, bedsores, and diaper rash). It also blocks the ultraviolet rays of the sun.

atomic number	30
relative atomic mass	65.37
relative density	7.14 (at 25°C)
melting point	419.5°C (787.1°F)
boiling point	908°C (1,666°F)

Zinc and health

Zinc is a trace element (second only to iron in its concentration in the body) that is essential for normal growth, development of the reproductive organs, normal function of the prostate gland, healing of wounds, and the manufacture of proteins and nucleic acid. Zinc is a cofactor that controls the activities of more than 100 enzymes and is involved in the functioning of the hormone insulin.

Small amounts of the element are present in a wide variety of foods; particularly rich sources include lean meat, wholemeal breads, whole grain cereals, dried beans, and seafoods. Beef, pork, and lamb contain more zinc than fish. The dark meat of a chicken has more zinc than the light meat.

Zinc deficiency

Zinc deficiency is rare, most cases occurring in people who are generally malnourished. Deficiency may also be caused by any disorder that causes malabsorption, by acrodermatitis enteropathica (a disorder of zinc absorption), or by increased zinc requirements due to cell damage (for example, as a result of a burn or in sickle cell anemia). Symptoms of deficiency include impairment of taste and loss of appetite; in severe cases, there may also be hair loss and inflammation of the skin, mouth, tongue, and eyelids.

Excess

Prolonged, excessive intake of zinc (usually through supplements) may interfere with the intestinal absorption of iron and copper, leading to a deficiency of these minerals and resultant symptoms of nausea, vomiting, fever, headache, tiredness, and abdominal pain.

Related category

• INORGANIC CHEMISTRY

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