The chemical element zinc is classed as a transition metal. It has been known since ancient times. Its discoverer and discovery date are unknown.
|Classification:||Zinc is a transition metal|
|Melting point:||419.53 oC, 692.68 K|
|Boiling point:||910 oC, 1183 K|
|Neutrons in most abundant isotope:||34|
|Electron configuration:||[Ar] 3d10 4s2|
|Density @ 20oC:||7.14 g/cm3|
|Atomic volume:||9.2 cm3/mol|
|Structure:||hcp: hexagonal close packed|
|Specific heat capacity||0.39 J g-1 K-1|
|Heat of fusion||7.322 kJ mol-1|
|Heat of atomization||131 kJ mol-1|
|Heat of vaporization||115.30 kJ mol-1|
|1st ionization energy||906.4 kJ mol-1>|
|2nd ionization energy||1733.2 kJ mol-1|
|3rd ionization energy||3832.6 kJ mol-1|
|Minimum oxidation number||0|
|Min. common oxidation no.||0|
|Maximum oxidation number||2|
|Max. common oxidation no.||2|
|Electronegativity (Pauling Scale)||1.65|
|Polarizability volume||6.4 Å3|
|Reaction with air||vigorous, ⇒ ZnO|
|Reaction with 15 M HNO3||vigorous, ⇒ Zn(NO3)2, NOx|
|Reaction with 6 M HCl||mild, ⇒ H2, ZnCl2|
|Reaction with 6 M NaOH||mild, ⇒ [Zn(OH4)]2-, H2|
|Oxide(s)||ZnO, ZnO2 (zinc peroxide)|
|Atomic radius||135 pm|
|Ionic radius (1+ ion)||–|
|Ionic radius (2+ ion)||88 pm|
|Ionic radius (3+ ion)||–|
|Ionic radius (1- ion)||–|
|Ionic radius (2- ion)||–|
|Ionic radius (3- ion)||–|
|Thermal conductivity||116 W m-1 K-1|
|Electrical conductivity||16.9 x 106 S m-1|
|Freezing/Melting point:||419.53 oC, 692.68 K|
Discovery of Zinc
Zinc ores have been used to make brass (a mixture of copper and zinc) and other alloys since ancient times.
A zinc alloy comprising 87.5% zinc was discovered in an ancient site in Transylvania.
Zinc smelting began in the 12th century in India by reducing calamine (zinc carbonate, ZnCO3) with wool and other organic materials.
The element name is reported to come from the old German word ‘zinke’ meaning pointed; a reference to the sharp pointed crystals formed after smelting.
Credit for isolating the metal is usually given to Andreas Marggraf in 1746, in Berlin. He heated a mixture of calamine ore and carbon in a closed vessel without copper to produce the metal.
Appearance and Characteristics
Zinc is not considered to be particularly toxic.
Zinc is essential for good health, but excess zinc is toxic and can cause nausea.
Zinc is a bluish-silver, lustrous metal that tarnishes in moist air, producing a layer of carbonate. It is somewhat brittle at room temperature but malleable above 100 oC.
Zinc reacts with both acids and alkalis.
Uses of Zinc
Zinc is used to galvanize iron to inhibit corrosion.
Zinc forms many alloys with other metals such as brass, German silver, nickel silver, typewriter metal and solders. Zinc alloys are used in die-castings for the car industry.
The metal acts as both the container and as an electrode in zinc-carbon batteries. The drawback of this dual use is that the electrode is consumed when the battery is in use, getting thinner until eventually the battery starts leaking.
Zinc is an essential trace element for animals and plants.
Zinc oxide, a white powder, is a versatile compound that has many uses.
It is used in sun block, make-up and in ointments such as calamine lotion.
Abundance and Isotopes
Abundance earth’s crust: 70 parts per million by weight, 22 parts per million by moles
Abundance solar system: 2 part per million by weight, 30 parts per billion by moles
Cost, pure: $5.30 per 100g
Cost, bulk: $0.18 per 100g
Source: Zinc is found in nature combined with other elements as ores. The main ores of zinc are sphalerite (sulfide), smithsonite (carbonate), hemimorphite (silicate), and franklinite (zinc, manganese, iron oxide).
Commercially, zinc is obtained from zinc sulfide minerals. The minerals are concentrated and then usually roasted to oxidize the zinc sulfide to zinc oxide. Zinc is then extracted by either large-scale electroplating (electrowinning) or by pyrometallurgy, where processing reduces zinc oxide with carbon or carbon monoxide at 950 oC into the metal.
Isotopes: Zinc has 25 isotopes whose half-lives are known, with mass numbers 57 to 83. Naturally occurring zinc is a mixture of five isotopes and they are found in the percentages shown: 64Zn (48.6%), 66Zn (27.9%), 67Zn (4.1%), 68Zn (18.8%) and 70Zn (0.6%). Over 48.6% of naturally occurring zinc is in the form of 64Zn.
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