Chemistry

An Overview about the Chemical Element Zinc



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Zinc

Symbol: Zn

Atomic Number: 30

Atomic Mass: 65.39 amu (atomic mass units)

Melting Point: 419.58 C (692.73 K, 787.24396 F)

Boiling Point: 907.0 C (1180.15 K, 1664.6 F)

Number of Protons: 30

Number of Electrons: 30

Number of Neutrons: 35

Classification: Transition Metal

Crystal Structure: Hexagonal

Density @293 K: 7.134 grams per cubic centimeter

Color: bluish

Zinc has been known and used in alloys for at least 2500 years. Alloyed to copper it forms brass and in the Old Testament of the Bible Tubal-Cain, said to be seven generations from Adam, is described as "an instructor of every artificer in brass and metal". An excavation of ruins in prehistoric Transylvania has found alloys containing 87% zinc. The earliest record of pure zinc comes from 13 century India where it was produced by the reduction of the mineral calamine with organic materials. In Europe the earliest record was from 1746 when Andreas Sigismund Marggraf heated calamine with charcoal to produce zinc metal. The name of the element is from the German "zink".

At room temperature zinc metal is brittle but at temperatures between 100 C (373 K, 212 F) and 150 C (423K, 302 F) it becomes malleable and ductile. It will burn giving of a red heat and clouds of white zinc oxide. Zinc can conduct electricity reasonably well.

Zinc is non ferromagnetic but ZrZn2, a compound of zinc and zirconium (which is also non ferromagnetic), is ferromagnetic at temperatures below minus 238 C (35 K, minus 397 F). This compound also has unusual optical, electrical, thermal and solid state properties. These properties are a matter of continuing investigation.

Zinc is a biologically essential element form both plants and animals. It is found in several enzymes and in insulin. Zinc deficiency in the diet of humans leads to stunted growth as well as sexual immaturity in males. The addition of zinc to diet can reverse the condition. Zinc metal is an irritant to human skin. Breathing an atmosphere containing fresh Zinc oxide (ZnO) can lead to a condition known as the "oxide shakes" or "zinc chills". It is recommended that atmospheric levels of zinc oxide should not exceed 5 micrograms per cubic meter of air.

Naturally occurring zinc is a combination of five isotopes. In order of abundance these isotopes are: zinc-64 (48.63%), zinc-66 (27.90%), zinc-68 (18.75%), zinc-67 (4.10%) and zinc-70 (0.62%). Zinc-70 is unstable with a half-life of 500,000,000,000,000 years the other four isotopes are stable. Other unstable isotopes with far shorter half-lives and mass numbers ranging from 54 to 83 are known.

Zinc can be extracted from a number of mineral ores by roasting the ore to extract zinc oxide which is then reduced with a carbon source such as coal. Zinc can also be purified by electrolysis. The ores from which zinc is extracted include sphalerite, smithsonite and calamine.

The main use for pure zinc metal is in galvanizing other metals such as iron to prevent corrosion. This can be one by dipping the metal into molten zinc or by electrolysis. Zinc is also used in the production of dry-cell batteries.

Many alloys are made using zinc. In addition to brass these alloys include nickel silver, typewriter metal, German silver and spring brass. An alloy of zinc, lead and tin forms a low melting point solder used to join electrical contacts and metal pipe work. Another alloy, made of 78% zinc and 22% aluminum, is known by the trade name Prestal. This alloy is almost as strong as steel but can be molded like a plastic.

Zinc oxide is the most useful of the elements compounds. It has a long list of everyday uses from pharmaceuticals to paint to printing ink and storage batteries.

Another compound, zinc sulfide will low in the ark if treated with ultraviolet light, X-rays or electrons. This property has led to its usage in fluorescent light tubes, television tubes and luminous watch or instrument dials. Combined with barium sulfate, zinc sulfide forms the pigment lithopone.

The compound zinc chloride is used to prevent damage to wood by decay or insects.

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