Chapter 3
Metals and Non-metals
Metals are lustrous, malleable (beaten into sheets), ductile (drawn into wires), sonorous, good conductors of heat and electricity, and mostly have high melting points.
EXCEPTIONS in metals: sodium and potassium are soft enough to cut with a knife; mercury is liquid at room temperature; gallium and caesium melt on the palm; lead and mercury are POOR conductors of heat. Silver is the best conductor of electricity, followed by copper.
Non-metals are dull, brittle, poor conductors, not sonorous, with low melting/boiling points. EXCEPTIONS: iodine is lustrous, graphite conducts electricity, bromine is a liquid, and diamond is the hardest natural substance with a very high melting point.
Metals + oxygen → metal oxides, which are generally BASIC. Sodium and potassium react with oxygen so fast at room temperature that they are stored under kerosene oil.
Non-metals + oxygen → non-metal oxides, which are generally ACIDIC — they dissolve in water to give acids: SO₂ + H₂O → H₂SO₃ and CO₂ + H₂O → H₂CO₃. (CO and NO are neutral oxides.) Non-metals do NOT react with water, and they do NOT react with dilute acids to release hydrogen, because a non-metal is an electron ACCEPTOR and cannot donate electrons to H⁺ ions.
AMPHOTERIC oxides (Al₂O₃ and ZnO) react with BOTH acids and bases to give salt and water — a favourite 1-mark question.
Most metal oxides are insoluble in water, but Na₂O and K₂O dissolve to form alkalis (NaOH, KOH).
Metals + water: K and Na react violently with COLD water (the hydrogen catches fire); Ca reacts less violently and FLOATS because hydrogen bubbles stick to its surface; Mg does not react with cold water but reacts with HOT water giving Mg(OH)₂ + H₂, and it FLOATS too for the same reason; Al, Zn and Fe react only with STEAM; Pb, Cu, Ag and Au do not react with water at all.
Metals + dilute acids → salt + hydrogen gas. Copper, silver and gold do NOT react. Nitric acid is a strong oxidising agent: it oxidises the hydrogen produced into water and is itself reduced to a nitrogen oxide (N₂O, NO or NO₂), so hydrogen is normally NOT evolved. EXCEPTION: magnesium and manganese react with VERY DILUTE nitric acid to give H₂ gas.
AQUA REGIA = 3 parts concentrated HCl : 1 part concentrated HNO₃ (freshly prepared). It is highly corrosive and can dissolve gold and platinum.
Reactivity series (most → least reactive): K, Na, Ca, Mg, Al, Zn, Fe, Pb, [H], Cu, Hg, Ag, Au. Metals ABOVE hydrogen displace H₂ from dilute acids; metals below it cannot.
Displacement: a more reactive metal displaces a less reactive one from its salt solution — Fe + CuSO₄ → FeSO₄ + Cu.
IONIC BOND: atoms transfer electrons to attain the nearest NOBLE-GAS (octet) configuration. Metals LOSE electrons to form positive ions (cations); non-metals GAIN electrons to form negative ions (anions), and the opposite charges attract. Na (2,8,1) → Na⁺ (2,8) + e⁻; Cl (2,8,7) + e⁻ → Cl⁻ (2,8,8), giving Na⁺Cl⁻. For a divalent metal: Mg (2,8,2) → Mg²⁺ (2,8) + 2e⁻, and those TWO electrons go to TWO chlorine atoms, giving Mg²⁺(Cl⁻)₂ = MgCl₂.
Properties of ionic compounds: hard, brittle crystalline solids; high melting and boiling points (strong inter-ionic attraction); generally soluble in water and insoluble in petrol/kerosene; conduct electricity in MOLTEN or AQUEOUS state but NOT as solids, because ions must be free to move.
MINERAL = any element or compound of a metal that occurs naturally in the earth's crust — very unreactive metals such as gold, silver and platinum occur in the free (native) state. ORE = a mineral from which the metal can be extracted profitably. GANGUE = the earthy impurities in an ore, removed during concentration.
Extraction depends on reactivity: LEAST reactive (Cu, Hg, Ag, Au) — by heating alone; MODERATELY reactive (Zn, Fe, Pb) — reduce the oxide with carbon; MOST reactive (K, Na, Ca, Mg, Al) — by ELECTROLYSIS only, because carbon cannot reduce them.
ROASTING = heating a SULPHIDE ore strongly in EXCESS air to give the oxide (2ZnS + 3O₂ → 2ZnO + 2SO₂). CALCINATION = heating a CARBONATE ore in LIMITED air to give the oxide (ZnCO₃ → ZnO + CO₂). Oxides are converted to the metal because they are easier to reduce.
THERMITE REACTION: Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat. It is so exothermic that the iron is produced molten — used to weld cracked railway tracks and machine parts on the spot.
ELECTROLYTIC REFINING: impure metal = ANODE, thin strip of pure metal = CATHODE, electrolyte = a solution of the metal salt. Pure metal deposits on the cathode; insoluble impurities settle below the anode as ANODE MUD.
CORROSION: iron rusts only when BOTH air (oxygen) and moisture are present; silver turns black (silver sulphide); copper develops a green coating (basic copper carbonate). Prevention: painting, oiling, greasing, galvanisation (zinc coating), chrome plating, anodising, and alloying.
ALLOY = a homogeneous mixture of a metal with another metal or a non-metal. Steel = iron + carbon (hard); stainless steel = iron + nickel + chromium (does not rust); brass = copper + zinc; bronze = copper + tin; solder = lead + tin (low melting point, used to weld electrical wires); an amalgam is an alloy containing mercury. An alloy's properties differ from its constituents — in particular its ELECTRICAL CONDUCTIVITY and MELTING POINT are LOWER than those of the pure metals, which is exactly why solder melts so easily.
Aluminium resists corrosion because a thin, tough layer of aluminium oxide forms on its surface and protects the metal underneath — ANODISING deliberately thickens this layer.
Metal + oxygen
2Mg + O₂ →Δ 2MgO
Dazzling white flame; MgO is a basic oxide.
Amphoteric oxide with acid
Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O
Behaves as a base here.
Amphoteric oxide with base
Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O
Behaves as an acid here — hence amphoteric.
Very reactive metal + cold water
2Na + 2H₂O → 2NaOH + H₂ + heat
So exothermic that the hydrogen catches fire.
Calcium + water
Ca + 2H₂O → Ca(OH)₂ + H₂
Calcium floats — hydrogen bubbles stick to its surface.
Iron + steam
3Fe + 4H₂O(steam) → Fe₃O₄ + 4H₂
Iron reacts only with steam, not with cold or hot water.
Metal + dilute acid
Zn + 2HCl → ZnCl₂ + H₂↑
Only metals above hydrogen in the reactivity series.
Displacement
Fe + CuSO₄ → FeSO₄ + Cu
Blue solution turns green; brown copper deposits.
Roasting (sulphide ore)
2ZnS + 3O₂ →Δ 2ZnO + 2SO₂
Heated strongly in EXCESS air.
Calcination (carbonate ore)
ZnCO₃ →Δ ZnO + CO₂
Heated in LIMITED air.
Reduction with carbon
ZnO + C → Zn + CO
Used for moderately reactive metals.
Metal low in the reactivity series
2HgS + 3O₂ →Δ 2HgO + 2SO₂ | 2HgO →Δ 2Hg + O₂
Cinnabar is roasted to the oxide; the oxide of such an unreactive metal is thermally unstable and breaks down to the metal on further heating — no separate reducing agent is needed.
Thermite reaction
Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat
Aluminium reduces iron oxide; molten iron welds railway tracks.
Electrolysis of molten NaCl
At cathode: Na⁺ + e⁻ → Na | At anode: 2Cl⁻ → Cl₂ + 2e⁻
The only way to obtain highly reactive metals.
Which of the following is the BEST conductor of electricity?
easyTry answering on paper first — then reveal the model answer. 📄
Solve in your notebook. Stuck? Take the hint before the solution. ✏️
1. An element X burns in air with a dazzling white flame to form a white powder Y. Y dissolves slightly in water to give a solution Z which turns red litmus blue. Identify X, Y and Z, and write the equation for the burning of X.
medium2. A piece of zinc is dropped into copper sulphate solution, and separately a piece of copper is dropped into zinc sulphate solution. State what happens in each case and write any equation that occurs.
medium3. Balance the equation for the reaction of iron with steam: Fe + H₂O → Fe₃O₄ + H₂.
medium4. Why can sodium not be extracted by reducing its oxide with carbon? Name the method used instead and write the electrode reactions for molten sodium chloride.
hard5. A metal M does not react with cold or hot water, but reacts with steam to give an oxide and hydrogen. When M is added to blue copper sulphate solution, copper is displaced and the solution turns PALE GREEN. Identify M and justify both observations using the reactivity series.
hard6. Name the constituents of stainless steel and explain why stainless steel is preferred over pure iron for making cutlery.
easy