Metals, Non-metals and Everyday Chemistry

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Metals and non-metals

Metals are lustrous, malleable, ductile, sonorous and good conductors; gold is the most ductile (1 g of gold can be drawn into a wire about 2 km long) and, with silver, the most malleable. Silver conducts electricity best, then copper. Sodium and potassium are soft enough to cut with a knife, mercury is liquid at room temperature, and gallium and caesium melt on the palm. Non-metals are usually brittle, dull and poor conductors, but iodine is lustrous, graphite conducts electricity and diamond is the hardest natural substance; bromine is the only liquid non-metal. Metal oxides are basic, some (aluminium and zinc oxides) amphoteric; non-metal oxides are acidic or neutral.

Reactivity and extraction

In the reactivity series K, Na, Ca, Mg, Al, Zn, Fe, Pb, (H), Cu, Hg, Ag, Au, the metals above hydrogen displace it from dilute acids. Sodium and potassium react violently with water and are kept in kerosene; white phosphorus, which catches fire in air, is kept in water. Ores are minerals from which metals are extracted profitably: bauxite (aluminium), haematite and magnetite (iron), cinnabar (mercury), galena (lead), zinc blende (zinc). Sulphide ores are roasted in excess air and carbonate ores calcined in limited air. The most reactive metals (K, Na, Ca, Mg, Al) are extracted by electrolysis of their molten compounds, zinc and iron by reduction with carbon, and copper is refined electrolytically. The thermit reaction of aluminium with iron oxide gives molten iron for welding railway tracks.

Alloys

An alloy is a homogeneous mixture of a metal with other metals or a non-metal; it is usually harder and more resistant to corrosion than the pure metal, with lower conductivity and melting point. Pure gold is 24 carat and too soft, so ornaments use 22 carat gold mixed with copper or silver. Stainless steel is iron with chromium and nickel; brass is copper and zinc; bronze copper and tin; German silver copper, zinc and nickel (with no silver); solder lead and tin (low melting point, for joining wires); duralumin aluminium with copper, magnesium and manganese (aircraft); nichrome nickel and chromium. An amalgam is any alloy of mercury.

Carbon and its allotropes

Carbon has valency 4 and links with itself into chains, branches and rings (catenation), which gives millions of carbon compounds. In diamond each carbon atom is bonded to four others in a rigid three-dimensional network, so it is the hardest natural substance and does not conduct electricity; it is used in jewellery and for cutting glass. In graphite each carbon is bonded to three others in hexagonal layers that slide over each other, so it is soft, slippery and a conductor; it is used as a lubricant, in electrodes and as pencil 'lead', which contains no lead at all. Fullerene C-60, a football-shaped molecule discovered in 1985, is named after the architect Buckminster Fuller.

Hydrocarbons

Alkanes have only single bonds (CnH2n+2: methane, ethane, propane, butane) and are saturated; alkenes have a double bond (CnH2n, such as ethene) and alkynes a triple bond (CnH2n-2, such as ethyne or acetylene, used in welding). Saturated hydrocarbons burn with a clean blue flame and unsaturated ones with a sooty flame. Methane is marsh gas and the main part of natural gas, CNG and biogas; LPG is mainly butane and propane, with ethyl mercaptan added so that leaks can be smelt. A 5 to 8 percent solution of ethanoic (acetic) acid is vinegar. Vegetable oils hydrogenated with a nickel catalyst give vanaspati ghee.

Soaps, detergents and plastics

Soaps are sodium or potassium salts of long-chain fatty acids, made by heating oils or fats with sodium hydroxide (saponification). A soap molecule has a water-loving ionic head and an oil-loving tail; the tails trap grease in clusters called micelles, which water washes away. In hard water, calcium and magnesium salts form scum with soap, but detergents still lather, though many do not biodegrade. Rubber is hardened by heating with sulphur (vulcanisation); rayon is artificial silk made from wood pulp and nylon a fully synthetic fibre. Thermoplastics such as polythene and PVC soften on heating and can be remoulded; thermosetting plastics such as bakelite (switches, pan handles) and melamine cannot.

Fuels and calorific value

Calorific value is the heat released by completely burning 1 kg of a fuel, in kJ/kg. NCERT lists cow dung cake 6000 to 8000, wood 17000 to 22000, coal 25000 to 33000, biogas 35000 to 40000, petrol, diesel and kerosene 45000, CNG 50000, LPG 55000 and hydrogen 150000, the highest, which is why liquid hydrogen is used as rocket fuel. Burning needs fuel, oxygen and heating to the ignition temperature; petrol and LPG catch fire easily because their ignition temperature is low. Incomplete burning gives poisonous carbon monoxide. The outermost, non-luminous zone of a candle flame is the hottest.

Everyday chemical names

Caustic soda is sodium hydroxide and caustic potash potassium hydroxide; limestone, chalk and marble are all calcium carbonate. Blue vitriol is copper sulphate, green vitriol ferrous sulphate and Epsom salt magnesium sulphate; sal ammoniac is ammonium chloride; muriatic acid is hydrochloric acid and oil of vitriol sulphuric acid; laughing gas is nitrous oxide; potash alum (fitkari) purifies water; and silver nitrate makes the indelible ink used in elections.

Key facts

1 g of gold can be drawn into a wire about 2 km long; silver is the best conductor of electricity, then copper; mercury is the only liquid metal and bromine the only liquid non-metal.
Sodium and potassium are kept in kerosene, white phosphorus in water; gold and platinum occur free in nature.
Ores: bauxite - aluminium; haematite, magnetite - iron; cinnabar - mercury; galena - lead; zinc blende, calamine - zinc.
Roasting: sulphide ore heated in excess air; calcination: carbonate ore heated in limited air; thermit (aluminium + iron oxide) welds railway tracks.
Ornament gold is 22 carat (pure 24 carat gold is too soft); solder = Pb + Sn; duralumin = Al + Cu + Mg + Mn; gun metal = Cu + Sn + Zn; amalgam = any alloy of mercury.
Diamond: each carbon bonded to 4 others, hardest, non-conductor; graphite: bonded to 3 in layers, conductor, lubricant, pencil 'lead'; fullerene C-60 discovered in 1985.
Alkane CnH2n+2, alkene CnH2n, alkyne CnH2n-2; vinegar is 5-8% acetic acid; ethyl mercaptan is added to LPG so that leaks can be smelt.
Soap forms scum in hard water, detergents do not; bakelite and melamine are thermosetting, polythene and PVC thermoplastic; Teflon coats non-stick pans.
Calorific value (kJ/kg): cow dung cake 6000-8000, wood 17000-22000, coal 25000-33000, petrol 45000, CNG 50000, LPG 55000, hydrogen 150000 (highest).
Names: blue vitriol CuSO4.5H2O, green vitriol FeSO4.7H2O, Epsom salt MgSO4.7H2O, sal ammoniac NH4Cl, muriatic acid HCl, oil of vitriol H2SO4, lunar caustic AgNO3.

Quick revision

Gold most ductile; silver best conductor; mercury liquid metal, bromine liquid non-metal; Na and K kept in kerosene; reactivity K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au; bauxite Al, haematite Fe, cinnabar Hg, galena Pb; thermit welds rails; ornaments 22 carat; solder Pb + Sn; diamond 4 bonds, graphite 3 bonds and conducts; C-60 found 1985; alkane CnH2n+2; vinegar 5-8% acetic acid; soap fails in hard water; bakelite thermosetting; hydrogen highest calorific value, 150000 kJ/kg.

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