Zinc (30)

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 galvanizing and helps to protect the iron from corrosion.

•Name: Zinc
•Symbol: Zn
•Atomic number: 30
•Atomic weight: 65.38
•Standard state: solid at 298 K
•CAS Registry ID: 7440-66-6
•Group in periodic table: 12
•Period in periodic table: 4
•Block in periodic table: d-block
•Color: bluish pale grey
•Classification: Metallic

Historical information

Zinc was discovered by Andreas Marggraf at 1746 in Germany. Origin of name is from the German word "zink". 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 a circle with a capital 'Z' inside.

Physical properties

•Melting point: 692.68 [or 419.53 °C (787.15 °F)] K
•Boiling point: 1180 [or 907 °C (1665 °F)] K
•Density of solid: 7140 kg m-3

Orbital properties

•Ground state electron configuration: [Ar].3d10.4s2
•Shell structure: 2.8.18.2
•Term symbol: 1S0

Isolation

Zinc metal is readily available commercially so it is not normally necessary to make it in the laboratory. Most zinc production is based upon sulfide 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 aluminum cathodes and lead alloyed with silver anodes gives pure zinc metal coated on the aluminum. 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%.

Interesting Facts:

1. Zinc (English) Zinc (French) Zink (Deutsch) Zinco (Italian/Spanish) Zink (Swedish)

2. Zinc's use has been traced back over 2500 years. The earliest documented use was in ancient ornaments and decorations found in eastern countries. Alchemists also produced zinc oxide, which they called “philosophers wool.”

3. Over fifty countries produce zinc, the largest being China, which tops 3,500,000 tons per year! A majority of zinc mined comes from underground sources in the form of zinc ore. After being mined, it must undergo processing as it isn't pure enough to be smelted.

4. Most zinc produced is used in galvanizing. This process is usually used to protect iron or steel from corrosion. Its properties make it more reactive than surrounding metals, meaning the corrosion (usually rust) is attracted to the zinc. This makes the metals much more durable in harsh environments, reducing the need for periodic replacement.

5. Brass alloy contains 3% to 45% zinc, with the remainder being copper. Brass is used to form many common items such as: musical instruments, decorations, building hardware, and tools. Other common zinc alloys include nickel silver, electrical solder, and a lead substitute in water pipes.

6. Zinc can help you stay young! It is believed to have anti-oxidant properties, which keep our skin and muscles from aging. It is available in dietary supplements, as well as in many natural foods. There is also a belief that zinc can help to shorten the length of the common cold as a homeopathic treatment.

7. Although zinc is helpful in moderation, an excess is dangerous both to humans and to the environment. It can reduce the rate our bodies absorb copper and iron, and inhalation has shown to cause a symptom called the “zinc shakes”. Processing facilities have also been shown to increase the heavy metal content in bodies of water. Additionally, high zinc levels in the soil can rob plants of the ability to absorb nutrients.

8. Back to science. Zinc's atomic number is 30, meaning an atom has thirty protons in the nucleus. Its atomic weight is 35.38, and has a melting point of 787.1 degrees Fahrenheit. It has a shiny bluish-white color in its pure form and is hard and brittle.

9. Zinc can only be created by nuclear fusion from supernovas. When massive stars reach the end of their life, they can explode and erupt their contents into space. This is the primary source of most heavy elements in the universe.