Metals and Non-metals

Malleability

The property of a metal that lets it be beaten into thin sheets without breaking. Gold and silver are the most malleable metals.

Ductility

The ability of a metal to be drawn into thin wires. Gold is the most ductile metal: about 2 km of wire can be drawn from a single gram of it.

Why can elements not be sorted into metals and non-metals by physical properties alone?

There are too many exceptions. Mercury is a liquid metal; gallium and caesium melt on the palm; sodium can be cut with a knife; lead and mercury conduct heat poorly. Among non-metals, iodine is lustrous, graphite conducts electricity and diamond is the hardest natural substance.

Amphoteric oxide

A metal oxide that reacts with both acids and bases to give a salt and water, unlike most metal oxides, which are only basic. Aluminium oxide and zinc oxide are examples.

Why are sodium and potassium kept immersed in kerosene oil?

They react so vigorously with oxygen that they catch fire if left in the open, and they react violently with water too. Keeping them under kerosene cuts them off from air and moisture and prevents accidental fires.

Why is hydrogen gas usually not evolved when a metal reacts with nitric acid?

Nitric acid is a strong oxidising agent. It oxidises the hydrogen produced to water and is itself reduced to an oxide of nitrogen (N2O, NO or NO2). Only magnesium and manganese give hydrogen, and only with very dilute nitric acid.

Reactivity series

Metals listed in decreasing order of reactivity: K, Na, Ca, Mg, Al, Zn, Fe, Pb, [H], Cu, Hg, Ag, Au. A metal can displace any metal below it from a salt solution, and those above hydrogen displace it from dilute acids.

Ionic compound

A compound formed when a metal hands electrons over to a non-metal, giving oppositely charged ions held by strong electrostatic attraction. Sodium chloride exists as an aggregate of Na+ and Cl- ions, not as molecules.

Why do ionic compounds such as sodium chloride have high melting and boiling points?

The attraction between their oppositely charged ions is very strong, so a considerable amount of energy is needed to break the inter-ionic forces before the solid can melt or the liquid boil.

Why does solid sodium chloride not conduct electricity, although its solution and its melt do?

Conduction needs charged particles that can move. In the solid the ions are held in a rigid structure and cannot move; in water, or when heat overcomes the attractions in the molten state, the ions move freely to the electrodes.

Ore

A mineral from which a particular metal can be profitably extracted because it contains a very high percentage of that metal. Every ore is a mineral, but a mineral is only an ore when extraction from it is worthwhile.

Gangue

The impurities such as soil and sand that contaminate an ore when it is mined. They must be removed before the metal is extracted, using differences in physical or chemical properties between gangue and ore.

How does a metal's position in the reactivity series decide how it is extracted?

Metals low in the series are reduced from their oxides by heating alone. Middle metals are converted to oxides and then reduced, usually with carbon. Metals at the top have more affinity for oxygen than carbon, so they are obtained by electrolysis of their molten chlorides or oxides.

Roasting

Converting a sulphide ore into its oxide by heating it strongly in the presence of excess air. For zinc: 2ZnS(s) + 3O2(g) --heat--> 2ZnO(s) + 2SO2(g).

Calcination

Converting a carbonate ore into its oxide by heating it strongly in limited air. It differs from roasting in the ore treated (carbonate, not sulphide) and in the air supply (limited, not excess).

How is mercury obtained from cinnabar (HgS), and what are the equations?

Mercury is low in the reactivity series, so heating alone is enough. Heated in air the ore first forms mercuric oxide: 2HgS(s) + 3O2(g) --heat--> 2HgO(s) + 2SO2(g). Further heating reduces the oxide: 2HgO(s) --heat--> 2Hg(l) + O2(g).

How is zinc obtained from zinc carbonate ore, and what are the equations?

The ore is calcined to the oxide, which is then reduced with carbon: ZnCO3(s) --heat--> ZnO(s) + CO2(g), followed by ZnO(s) + C(s) --> Zn(s) + CO(g).

How is sodium obtained from sodium chloride, and what happens at each electrode?

By electrolysis of molten sodium chloride. Sodium is deposited at the cathode: Na+ + e- --> Na. Chlorine is liberated at the anode: 2Cl- --> Cl2 + 2e-.

What is the thermit reaction, and what is its equation?

Iron(III) oxide heated with aluminium, which displaces the less reactive iron: Fe2O3(s) + 2Al(s) --> 2Fe(l) + Al2O3(s) + heat. So much heat is released that the iron is molten, which is why it is used to join railway tracks.

How is an impure metal such as copper or zinc refined by electrolysis?

Use the impure metal as anode, a thin pure strip of it as cathode, and a solution of one of its salts as electrolyte. Current dissolves metal from the anode while an equal amount of pure metal is deposited on the cathode; soluble impurities stay dissolved and insoluble ones collect beneath the anode as anode mud.

How does the three test-tube experiment show the conditions needed for iron to rust?

Nails rust only in the tube exposed to both air and water. They do not rust in boiled water sealed under oil, which has no dissolved air, nor in dry air kept dry by anhydrous calcium chloride. Both air and moisture are therefore needed.

Galvanisation

Covering iron or steel with a thin zinc layer to stop it rusting. The article remains protected even where the zinc coat gets broken.

Alloy

A uniform mixture of two or more metals, or of a metal with a non-metal. Alloying changes properties: pure iron is soft, but with about 0.05% carbon it becomes hard and strong steel, and alloys conduct electricity less and melt lower than pure metals.

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