Metals, in their pure state, have a shining surface. This property is called metallic lustre. The ability of metals to be drawn into thin wires is called ductility. Gold is the most ductile metal.
It is because of their malleability and ductility that metals can be given different shapes according to our needs.
Metals are good conductors of heat and have high melting points. The best conductors of heat are silver and copper. Lead and mercury are comparatively poor conductors of heat.
The non-metals are either solids or gases except bromine which is a liquid. Most non-metals produce acidic oxides when dissolve in water. On the other hand, most metals, give rise to basic oxides.
Elements can be more clearly classified as metals and non-metals on the basis of their chemical properties.
Almost all metals combine with oxygen to form metal oxides.
Metal + Oxygen → Metal oxide
For example, when copper is heated in air, it combines with oxygen to form copper(II) oxide, a black oxide.
2Cu + O2 → 2CuO
Some metal oxides, such as aluminium oxide, zinc oxide show both acidic as well as basic behaviour. Such metal oxides which react with both acids as well as bases to produce salts and water are known as amphoteric oxides.
Most metal oxides are insoluble in water but some of these dissolve in water to form alkalis. Different metals show different reactivities towards oxygen.
Metals react with water and produce a metal oxide and hydrogen gas. Metal oxides that are soluble in water dissolve in it to further form metal hydroxide. But all metals do not react with water.
Metal + Water → Metal oxide + Hydrogen
Metal oxide+ Water → Metal hydroxide
Metals like potassium and sodium react violently with cold water. In case of sodium and potassium, the reaction is so violent and exothermic that the evolved hydrogen immediately catches fire.
Metals like aluminium, iron and zinc do not react either with cold or hot water. But they react with steam to form the metal oxide and hydrogen.
Hydrogen gas is not evolved when a metal reacts with nitric acid. It is because HNO3 is a strong oxidising agent. It oxidises the H2 produced to water and itself gets reduced to any of the nitrogen oxides (N2O, NO, NO2).
Reactive metals can displace less reactive metals from their compounds in solution or molten form.
The reactivity series is a list of metals arranged in the order of their decreasing activities.
The compounds formed in this manner by the transfer of electrons from a metal to a non-metal are known as ionic compounds or electrovalent compounds. following general properties for ionic compounds -
Physical nature: Ionic compounds are solids and are somewhat hard because of the strong force of attraction between the positive and negative ions.
Melting and Boiling points: Ionic compounds have high melting and boiling points.
Solubility: Electrovalent compounds are generally soluble in water and insoluble in solvents such as kerosene, petrol, etc.
Conduction of Electricity: The conduction of electricity through a solution involves the movement of charged particles. A solution of an ionic compound in water contains ions, which move to the opposite electrodes when electricity is passed through the solution.
The earth's crust is the major source of metals. Seawater also contains some soluble salts such as sodium chloride, magnesium chloride, etc. The elements or compounds, which occur naturally in the earth's crust, are known as minerals.
Some metals are found in the earth's crust in the free state. Some are found in the form of their compounds. The metals at the bottom of the activity series are the least reactive. on the basis of reactivity, we can group the metals into the following three categories −
Metals of low reactivity;
Metals of medium reactivity;
Metals of high reactivity.
Different techniques are to be used for obtaining the metals falling in each category.
Ores mined from the earth are usually contaminated with large amounts of impurities such as soil, sand, etc., called gangue.
The impurities must be removed from the ore prior to the extraction of the metal. The processes used for removing the gangue from the ore are based on the differences between the physical or chemical properties of the gangue and the ore.
Metals low in the activity series are very unreactive. The oxides of these metals can be reduced to metals by heating alone
The metals in the middle of the activity series such as iron, zinc, lead, copper, are moderately reactive. These are usually present as sulphides or carbonates in nature. It is easier to obtain a metal from its oxide, as compared to its sulphides and carbonates.
The sulphide ores are converted into oxides by heating strongly in the presence of excess air. This process is known as roasting. The carbonate ores are changed into oxides by heating strongly in limited air. This process is known as calcination.
The metals high up in the reactivity series are very reactive. They cannot be obtained from their compounds by heating with carbon. For example, carbon cannot reduce the oxides of sodium, magnesium, calcium, aluminium, etc., to the respective metals. This is because these metals have more affinity for oxygen than carbon. These metals are obtained by electrolytic reduction.
The metals produced by various reduction processes described above are not very pure. They contain impurities, which must be removed to obtain pure metals. The most widely used method for refining impure metals is electrolytic refining.
The rusting of iron can be prevented by painting, oiling, greasing, galvanising, chrome plating, anodising or making alloys.
Galvanisation is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc.
An alloy is a homogeneous mixture of two or more metals, or a metal and a nonmetal. It is prepared by first melting the primary metal, and then, dissolving the other elements in it in definite proportions. It is then cooled to room temperature.
If one of the metals is mercury, then the alloy is known as an amalgam. The electrical conductivity and melting point of an alloy is less than that of pure metals.