Metals and Non-metals — Notes

Metals are generally lustrous, hard, malleable (beaten into sheets), ductile (drawn into wires), sonorous (ring when struck), good conductors of heat and electricity, and have high melting points. Gold and silver are the most malleable and ductile; silver and copper are the best conductors.

Non-metals are solids or gases (bromine is a liquid), generally dull, brittle and poor conductors.

Exceptions

• Mercury is a liquid metal; gallium and caesium melt on the palm.
• Sodium and potassium are soft (cut with a knife) and have low melting points.
• Lead and mercury are poor conductors of heat.
• Iodine is lustrous; graphite conducts electricity; diamond is the hardest natural substance with a very high melting point.

With oxygen: metal + oxygen → metal oxide (basic). Potassium and sodium catch fire in air and are stored under kerosene; magnesium burns with a dazzling flame; aluminium, zinc and lead form a protective oxide layer; iron filings burn; copper forms black CuO; silver and gold do not react.

Amphoteric oxides ($\ce{Al2O3}$, $\ce{ZnO}$) react with both acids and bases to give salt and water. Soluble metal oxides (e.g. $\ce{Na2O}$, $\ce{K2O}$) give alkalis.

With water: K, Na (violent, hydrogen catches fire) and Ca (steady, floats) react with cold water to give hydroxide + hydrogen; Mg reacts with hot water (floats); Al, Zn, Fe react only with steam to give oxide + hydrogen; Pb, Cu, Ag, Au do not react.

With dilute acids: metals above hydrogen give salt + hydrogen; vigour Mg > Al > Zn > Fe; copper does not react. Nitric acid is an oxidising agent and usually gives no hydrogen (except Mg and Mn with very dilute nitric acid).

With salt solutions: a more reactive metal displaces a less reactive one.

The reactivity series lists metals in order of decreasing reactivity, worked out from their reactions with water, acids and salt solutions:

K > Na > Ca > Mg > Al > Zn > Fe > Pb > [H] > Cu > Hg > Ag > Au

• Metals above hydrogen displace hydrogen from dilute acids; those below do not.
• A metal displaces any metal below it from a solution of its salt.
• The higher the metal, the harder it is to extract from its compounds.

Atoms react to reach a stable noble-gas configuration (an octet, or a duplet for helium). Metals lose electrons to form cations; non-metals gain electrons to form anions. The electrostatic attraction between them is an ionic (electrovalent) bond.

• Na (2, 8, 1) → $\ce{Na+}$ (2, 8); Cl (2, 8, 7) → $\ce{Cl-}$ (2, 8, 8): $\ce{NaCl}$.
• Mg (2, 8, 2) gives one electron to each of two Cl atoms: $\ce{MgCl2}$.

Properties of ionic compounds: hard, brittle solids; high melting and boiling points (strong attraction between ions); generally soluble in water, insoluble in kerosene and petrol; conduct electricity when molten or in solution (ions free to move) but not in the solid state.

Minerals are naturally occurring compounds; ores are minerals from which metals are extracted profitably; gangue is the earthy impurity.

Steps: (1) concentration (enrichment) of the ore; (2) extraction by a method that depends on reactivity; (3) refining.

• Low reactivity (Hg, Cu): heating the ore alone. Cinnabar gives mercury; copper sulphide gives copper.
• Middle (Zn, Fe, Pb): sulphide ores are roasted (strong heating in excess air); carbonate ores are calcined (strong heating in limited air); the oxide is reduced with carbon, or with a more reactive metal such as aluminium (thermit reaction, used to weld rails).
• High (K, Na, Ca, Mg, Al): electrolytic reduction of the molten chloride or oxide; the metal forms at the cathode.

Electrolytic refining of copper: anode — impure copper; cathode — thin strip of pure copper; electrolyte — acidified copper sulphate solution. Pure copper deposits on the cathode; soluble impurities stay in solution; insoluble ones collect below the anode as anode mud.

Corrosion: silver turns black (silver sulphide), copper gets a green coat (basic copper carbonate), iron rusts. Iron rusts only when both air (oxygen) and water are present.

Prevention: painting, oiling, greasing, galvanising (coating with zinc; protects even when scratched because zinc is more reactive), chrome plating, anodising, alloying.

Alloys are homogeneous mixtures of a metal with other metals or a non-metal. Their electrical conductivity and melting point are lower than those of the pure metals.

• Steel: iron + carbon; stainless steel: iron + nickel + chromium.
• Brass: copper + zinc; bronze: copper + tin; solder: lead + tin (low melting point, joins wires).
• Pure gold is 24 carat and soft; 22-carat gold has 22 parts gold and 2 parts silver or copper.
• An alloy of mercury is an amalgam.