Metals, Non-Metals & Carbon Compounds

Metals and non-metals

Chemical properties of metals

• With oxygen: metal + O₂ → metal oxide (basic). $2\text{Mg}+{\text{O}}_2\to 2\text{MgO}$. Sodium and potassium burn in air (stored under kerosene); iron burns as filings; copper turns black (CuO) on heating; aluminium forms a protective oxide layer (anodising thickens it). Amphoteric oxides (Al₂O₃, ZnO) react with both acids and bases.
• With water: Na and K react violently with cold water; Ca less so; Mg with hot water; Al, Zn, Fe with steam; Cu, Ag, Au do not react.
• With dilute acids: metals above hydrogen liberate H₂; copper, silver and gold do not (except with oxidising acids like nitric acid).
• With salt solutions: displacement of a less reactive metal by a more reactive one.

Reactivity series

K > Na > Ca > Mg > Al > Zn > Fe > Pb > (H) > Cu > Hg > Ag > Au

Ionic compounds

Formed when a metal transfers electrons to a non-metal. They are hard, brittle crystalline solids with high melting and boiling points, are soluble in water and conduct electricity in the molten state and in solution (not as solids).

Occurrence and extraction of metals

• Minerals are naturally occurring compounds of metals; an ore is a mineral from which the metal can be profitably extracted. Gangue is the impurity in the ore.

Steps in extraction

1. Concentration of the ore (hand-picking, washing, magnetic separation, froth flotation for sulphide ores).
2. Conversion to oxide: calcination (heating carbonate ores in limited or no air: ZnCO₃ → ZnO + CO₂) or roasting (heating sulphide ores in excess air: 2ZnS + 3O₂ → 2ZnO + 2SO₂).
3. Reduction of the oxide to the metal:
   • Low-reactivity metals (Hg, Cu): heating alone: 2HgS + 3O₂ → 2HgO + 2SO₂; 2HgO → 2Hg + O₂.
   • Medium-reactivity metals (Zn, Fe, Pb): reduction by carbon (coke) or carbon monoxide: ZnO + C → Zn + CO; Fe₂O₃ + 3CO → 2Fe + 3CO₂ (blast furnace). The thermite reaction: Fe₂O₃ + 2Al → Al₂O₃ + 2Fe (used to weld railway tracks).
   • High-reactivity metals (K, Na, Ca, Mg, Al): electrolysis of the molten compound — aluminium by electrolysis of alumina dissolved in molten cryolite (Hall–Héroult process); sodium by electrolysis of molten NaCl (Down's process).
4. Refining: electrolytic refining (impure metal as anode, pure metal as cathode: copper, zinc, silver, gold); distillation (Zn, Hg).

Iron and steel: pig iron (cast iron) has 3–4 % carbon; wrought iron is almost pure; steel has 0.1–1.5 % carbon. Blast furnace flux: limestone; slag: calcium silicate.

Corrosion and alloys

Corrosion (rusting of iron, tarnishing of silver, green coating on copper) and its prevention are described in the Chemical Reactions note.

Alloys are homogeneous mixtures of a metal with other metals or non-metals; they are harder, stronger, more corrosion-resistant and have lower melting points than pure metals.

Non-metals

• Hydrogen, carbon, nitrogen, oxygen, phosphorus, sulphur, the halogens and noble gases.
• With oxygen: form acidic or neutral oxides (CO₂, SO₂, P₂O₅). They accept electrons to form anions; not in the reactivity series.
• Sulphur is used in vulcanisation of rubber, gunpowder and matches; phosphorus in matches (red phosphorus on the box) and fertilisers; nitrogen in fertilisers and ammonia; chlorine for disinfecting water.

Carbon and its compounds

Carbon (valency 4) forms a vast number of compounds because of catenation (the ability to form long chains and rings by bonding with itself) and its tetravalency; it forms strong single, double and triple covalent bonds. It occurs as diamond, graphite, fullerenes (C₆₀, buckminsterfullerene), graphene and carbon nanotubes.

• Covalent compounds have low melting and boiling points, are poor conductors of electricity and are generally insoluble in water.
• Hydrocarbons: compounds of carbon and hydrogen. Saturated (alkanes): single bonds only, general formula ${\text{C}}_n{\text{H}}_{2n+2}$ (methane CH₄, ethane C₂H₆, propane C₃H₈, butane C₄H₁₀). Unsaturated: alkenes (double bond, ${\text{C}}_n{\text{H}}_{2n}$: ethene, propene) and alkynes (triple bond, ${\text{C}}_n{\text{H}}_{2n-2}$: ethyne/acetylene, used in welding). Aromatic: benzene (C₆H₆).
• Homologous series: a family of compounds with the same functional group and general formula, with successive members differing by a –CH₂– unit (14 u).
• Isomers: compounds with the same molecular formula but different structures (butane and isobutane).
• Functional groups: alcohol (–OH), aldehyde (–CHO), ketone (>C=O), carboxylic acid (–COOH), halo (–Cl, –Br), ester (–COO–), amine (–NH₂).

• Combustion: carbon compounds burn in oxygen to give CO₂, water, heat and light; saturated hydrocarbons burn with a clean blue flame; unsaturated ones with a yellow sooty flame (incomplete burning).
• Addition reaction: unsaturated hydrocarbons add hydrogen in the presence of nickel — hydrogenation of vegetable oils to make vanaspati ghee.
• Substitution reaction: alkanes react with chlorine in sunlight.

Ethanol reactions

• Ethanol + sodium → sodium ethoxide + hydrogen.
• Ethanol → ethene (with conc. H₂SO₄ at 443 K, dehydration).
• Ethanol + ethanoic acid → ester (esterification).
• Ethanol → ethanoic acid (oxidation with alkaline KMnO₄ or acidified K₂Cr₂O₇).

Soaps and detergents

Soap is the sodium or potassium salt of a long-chain fatty acid; it is made by the saponification of fats or oils with NaOH. It has a hydrophobic tail and a hydrophilic head, and forms micelles around grease. Soaps form scum in hard water (they react with calcium and magnesium salts); detergents (sodium alkyl sulphonates) do not.

Fuels