SSC Chemistry Metals and Non-metals / धातु और अधातु Metals and Non-metals

Metals and Non-metals

• Metals and Non-metals: There are more than 114 elements present in the periodic table. These elements can be broadly classified into two categories i.e., metals and non-metals. Out of 114 elements, 22 are non-metals.
• Physical properties of metals:

(i) They are usually shiny i.e. have a metallic luster.

(ii) Metals have a high density

(iii) Metals are ductile i.e. they can be drawn into wires.

(iv) Metals are malleable i.e. they can be founded into thin sheets.

(v) Metals are good conductors of electricity.

(vi) Metals have high melting point and are generally in solid state at room temperature.

(vii) Metals are good conductors of heat and sound.

• Uses of metals:

(i) Metals are very important for modern humans it is not possible to imagine our life without them.

(ii) Metals are used in manufacturing of bridges, railways, aeroplanes, diesel mobile units (DMU), electric mobile units (EMU), motor cars, electric motors, telephones, televisions, interplanetary space vehicles, or even common articles like cooking utensils and coins.

(iii) Metals are very important for the economy of a country. Some metals, such as titanium, chromium, manganese and zirconium are strategic metals. These metals and their alloys find wide applications in atomic energy, space science projects, jet engines and high grade steels.

(iv) Gold and silver ornaments are obtained from small pieces of metals by hammering.

• Noble metal: Noble metals are metals that are resistant to corrosion or oxidation, unlike most base metals. Examples include tantalum, gold, platinum, and rhodium.
• Precious metal: A precious metal is a rare metallic chemical element of high economic value precious metals include the platinum group metals: ruthenium, rhodium, palladium, osmium, indium, and platinum, of which platinum is the most widely traded.
• Alloy: An alloy is a mixture of two or more elements in solid solution in which the major component is a metal. Most pure metals are either too soft, brittle or chemically reactive for practical use. Combining different ratios of metals as alloys modify the properties of pure metals to produce desirable characteristics. The aim of making alloys is generally to make them less brittle, harder, resistant to corrosion, or have a more desirable color and luster. Examples of alloys are steel (iron and carbon), brass (copper and zinc), bronze (copper and tin), and duralumin (aluminium and copper).

• Physics properties of non-metals:

(i) They are dull, however diamond, graphite and iodine are lustrous.

(ii) They are poor Coonductors of heat and electricity. Graphite is a good conductor.

(iii) They are weak and brittle (they easily break or shatter).

(iv) They have a low density (they feel light for their size).

(v) They do not make a ringing sound when they are hit.

(vi) Melting points and boiling points are usually low.

(vii) Non-metals are usually soft. (Diamond is an exception, it is quite hard. It is a crystalline solid).

(viii) They exist in allotropic forms.

• Uses of Non-Metals

(i) Oxygen is essential for survival of life.

(ii) Hydrogen is used to convert vegetable oil into vegetable ghee by hydrogenation.

(iii) Nitrogen is used to preserve food and for manufacturing proteins by plants.

(iv) Carbon in the form of diamond is used for cutting rocks and in the form of graphite as electrode and in manufacture of lead pencils.

(v) Sulphur is used in vulcanization of rubber, as fungicide and in manufacture of dyes, gun powder etc.

(vi) Chlorine is used as water disinfectant and in the manufacture of pesticides like gammaxene.

• Extraction of Metals

(i) Minerals: The natural substance in which the metals or their compounds occur in the earth is called minerals.

(ii) Ores: The minerals from which the metals can be conveniently and economically extracted are called ores.

(iii) Native ores: These ores contain metals in the free-state, e.g., silver, gold, platinum, etc.

(iv) Metallurgy: W whole process of obtaining a pure metal from one of its ore is known as metallurgy.

(v) Gangue or matrix: Ores usually contain soil, sand, stones and others useless silicates. These undesired impurities present m ores are called gangue or matrix.

(vi) The removal of unwanted earthy and silicious impurities from the ore is called ore-dressing or concentration of ores and the process used to concentrate an ore is called the benefication process.

(vii) Concentration of ore is achieved by

• (a) Physical methods,
• (b) Chemical methods

(viii) Physical methods are:

• (a) Hand-picking: It is used in the case when the impurities are quite distinct from the ore so that these may be differentiated by naked eye.
• (b) Hydraulic washing or Levigation or Gravity separation: The separation is based on the difference in the specific gravities of the gangue particles and the ore particles.
• (c) Electromagnetic separation: When one component either the ore or impurity is magnetic in nature, this method can be used for separation.
• (d) Froth floatation process: This method is used for the concentration of sulphide ores.

(ix) Chemical method (Leaching) involves the treatment of the ore with a suitable reagent as to make it soluble while impurities remain insoluble. The ore is recovered from the solution by suitable chemical method.

(x) Extraction process used to obtain metals in free-state from concentrated ores is called extraction.

(xi) Extraction of crude metal from the concentrated ore involves following chemical processes.

• (a) Conversion of ore into metallic oxides.
• Calcination involves heating the ore below its fusion temperature in the absence of air. It can remove moisture from hydrated oxide or\[C{{O}_{2}}\] from carbonates. It makes the ore porous.
• Roasting is the heating of the ore in the presence of air below its fusion temperature.
• (b) Reduction to free metal:
• Smelting: This involves the reduction of the ore to the molten metal at a high temperature. For the extraction of electropositive metals such as Pb, Fe, Sn, powerful reducing agent like C, \[C{{H}_{2}}\] CO, Al, Mg, etc., are used.
• Self reduction process: These processes are also called auto-reduction process.
• Electrolytic process: The oxides of highly electropositive metals like Na, K, Mg, Ca, Al, etc., are extracted by electrolysis of their oxides, hydroxides or chlorides in fused state. For example, Al is obtained by the electrolysis of alumina mixed with cryolite.

(xii) Refining is the process of purifying the extracted metals.

(xiii) Chromatography is based on the principle that the different components of a mixture are adsorbed to different extents on an adsorbent.

• Corrosion of Metals: Corrosion is an oxidation reaction with atmospheric oxygen in the presence of water on the surface of a metal.

Rusting is \[Fe(s)+\frac{3}{2}{{O}_{2}}(g)+x{{H}_{2}}O(l)\to F{{e}_{2}}O.x{{H}_{2}}O(s)\] i.e., rust is hydrated iron (III) oxide.

• Prevention of Corrosion: Iron and steel (alloy of iron) are most easily protected by paint which provides a barrier between the metal and air/water. Moving parts on machines can be protected by a water repellent oil or grease layer. Other important methods are

(i) Alloying: Iron or steel along with other metals can also be protected by 'alloying' or mixing with other metals (e.g., chromium) to make non-rusting alloys.

(ii) Galvanizing: Coating iron or steel with a thin zinc layer is called 'galvanizing’.

• Purity of Gold:

24-Carat gold: The carat (abbreviation ct or Kt) is a measure of the purity of gold alloys. Carat is used to refer to the measure of mass for gemstones.