Chemical and physical properties of zinc
How it reacts with other elements
Thanks to its chemical and physical properties, zinc is a material that is suitable in a diverse range of human activities.
How the element was discovered
Alloys containing zinc have been used by humanity since ancient times. The name of the metal (zincum) is encountered in the works of Paracelsus, a doctor who lived in the 16th century. At around the same time the metal began to be used by craftsmen in China, who forged coins from it. Later zinc was discovered in Europe, and the metal began to be widely used in various spheres.
The first known alloy of zinc was brass, which was first used in Cyprus, and then in England, Germany and other European nations.
The name of the metal comes from the word zincum, the etymology of which is not entirely clear. According to various theories, zincum can be translated as “white coating” (from Latin), while the word “zinke” meant “pointed” in German. The metal was given its modern name in the 20th century.
Characteristics of the element
Zinc is located in the second group, side subgroup of the periodic table. Its atomic mass is 65.38, and atomic number is 30. The electron configuration of the outer shell of the atom is 4s2. Its constant and only oxidation state is +2. In the periodic table, zinc, cadmium, copper, manganese, chromium and others are transition metals. They include elements in which electrons fill the outer and next-to-outer d and f subshells.
Metals of the platinum group are also transition metals – ruthenium, rhodium, platinum, osmium, palladium and iridium. They form complex compounds, in which they act with different coordination numbers as a complexing agent. These properties are also characteristic for zinc. There are five stable isotopes in nature with mass numbers from 64 to 70. Radioactive 65Zn has a half-life of 244 days.
Physical properties of zinc
Characteristics of the element:
- density – 7.13 g/cm³;
- color – bluish-white;
- zinc is a low-melting metal, with a melting point of 420 °C;
- the elasticity and malleability of the metal increases when it is heated to 100 °C;
- the boiling point of the simple substance is 906 °C;
- when heated to 200 °C, zinc loses its elasticity and turns to a gray powder;
- the metal has a high heat capacity and heat conductivity;
- zinc is a good conductor.
Chemical properties of the element
In ordinary conditions, the swift reaction of zinc with air takes place – the metal is covered with a dull gray coating (zinc oxide). Zinc also reacts with other substances: halogens, oxygen, chalcogens, alkalis, acids, ammonium and ammonia salts, and also with weaker metals. Zinc does not react with nitrogen, and is an amorphic metal. In reactions with alkalis, the element forms complex compounds – hydroxo-zincates.
Examples of several reactions with zinc
The basis of White’s discovery of the zinc ion was the reaction with benzoin.
Solutions of sodium thiosulfate, sodium silicate, magnesium chloride and benzoin in ethyl alcohol are gradually added to the solution under investigation. The magnesium hydroxide released absorbs the complex of zinc and benzoin, and the sediment glows with a green light in ultraviolet rays.
When an electric current is passed through a solution containing ions, i.e. through the electrolyte solution, chemical reactions take place on the electrodes, and the degree of the transformation of this reaction is connected with the amount of electricity, according to the laws of electrolysis discovered by Faraday. For example, if the solution contains a zinc salt, then on the cathode (the electrode to which electrons move), the zinc ions turn to metallic zinc, which are released on the electrode. This reaction can be regarded as the reduction of zinc ions by electrolysis.
Reduction of nitro group. A few crystals or drops of nitro compounds are mixed with 0.5 M HCl (r=1.12), and metal zinc is added. The reaction takes place violently. When the reaction dies down, the mixture is heated until the smell of the nitro compound disappears. After cooling, several drops of the obtained solution are added to an alkaline solution of calcium hypochlorite Са(OСl)₂. In the course of the reaction, the nitro group is reduced to an amino group.
Petten once studied the behavior of the metal in relation to hydrogen chloride dissolved in various organic liquids. The hydrogen chloride solution in thoroughly dried benzol reacted energetically with zinc, but the reaction stopped as soon as the surface was covered with a film of solid zinc chloride, which dissolves poorly in benzo. If water is added, which dissolves the zinc chloride, the reaction resumes. If we ignore this delay in the reaction products, we may state that hydrogen chloride solutions in organic liquid strongly react with zinc. A solution in dry chloroform reacts with zinc just as strongly as normal aqueous hydrochloric acid, although the chloroform solution has a very low electroconductivity, lower than the electroconductivity of the air gap. This shows that the corrosion process is not necessary connected with the flow of an electric current.
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Main categories of compounds:
- zinc carbides;
- zinc halogenides (fluoride, chloride, bromide, iodide);
- selenide, sulfite, zinc arsenide;
- thiocyanates, thiosulfates and cyanides – in aqueous solution in the form of corresponding complexes;
- ammonia complexes – formed from the interaction of zinc with ammonia solution;
- amphoteric compounds of zinc oxide and hydroxide – used for obtaining complexes of hydroxo-zincates.
Most zinc compounds are used in the chemical industry and other fields – organic synthesis, technology, the paint and varnish industry. Zinc oxide is also used in medicine – it has an anti-inflammatory effect, and kills bacteria.