Secondary 5 Chemistry

A chemical bond formed when two non-metal atoms share a pair of electrons.

A pair formed by one electron from each atom, attracted to both nuclei.

A diagram using dots and crosses for outer-shell electrons to show bonding in a molecule.

A covalent bond formed by one shared pair, e.g. the O—H bonds in water.

A covalent bond of two shared pairs, as in O₂ and CO₂.

A stable outermost shell of eight electrons, like a noble gas.

A substance made of separate molecules held together only by van der Waals' forces, e.g. CO₂ and iodine.

Weak attractions between molecules, far weaker than covalent bonds, responsible for low melting points.

A structure in which countless atoms are joined by covalent bonds throughout, e.g. diamond and quartz.

The mineral form of silicon dioxide, a giant covalent solid, hard and heat-resistant.

The electrostatic attraction between metal cations and delocalised electrons.

Outer-shell electrons that have left their atoms and flow freely through the metal; also called free electrons.

Metal cations in layered lattices immersed in a sea of delocalised electrons.

The ability to be drawn into wires without breaking, e.g. copper wire.

The ability to be rolled into sheets without shattering, e.g. aluminium foil.

The ability to carry a current; metals conduct via moving delocalised electrons.

The ability to transfer heat; metals conduct via free electrons and vibrating cations.

A mixture of a metal with other metals or non-metals; usually harder than the pure metal.

An alloy of copper and zinc, harder than pure copper, used in instruments and locks.

Steel with chromium and nickel added, highly rust-resistant, used in cutlery and medical tools.

Metals ranked from most to least reactive, also called the metal activity series; carbon and hydrogen are included as references.

A reaction in which a more reactive metal displaces a less reactive metal from its salt solution.

Rock bearing metal compounds from which the metal is extracted, e.g. haematite, bauxite.

Reducing a metal from its ore; the method depends on the metal's reactivity.

Gaining electrons (or losing oxygen); extracting a metal means reducing its ions to the metal.

An iron ore of mainly iron(III) oxide (Fe₂O₃), the feedstock of the blast furnace.

A large furnace in which iron ore is reduced by carbon monoxide at high temperature.

Decomposition driven by an electric current; reactive metals are extracted by electrolysis of molten compounds.

Metals occurring as compounds in nature; reactive metals exist almost entirely in this state.

Metals occurring as the uncombined element in nature, e.g. native gold and silver.

A substance that releases hydrogen ions in water; its solution has pH below 7 and turns blue litmus red.

A substance that reacts with an acid — commonly metal oxides, hydroxides and carbonates.

A soluble base whose solution contains hydroxide ions and turns red litmus blue, e.g. sodium hydroxide.

The H⁺(aq) released by acids in water, the source of all acidic properties.

The OH⁻(aq) released by alkalis in water, the source of all alkaline properties.

A dye showing different colours in acidic and alkaline solutions, e.g. litmus, phenolphthalein, methyl orange.

A common indicator: red in acid, blue in alkali.

A 0–14 scale of acidity: below 7 acidic, above 7 alkaline, 7 neutral.

An acid that dissociates completely in water, e.g. hydrochloric acid, as opposed to partially dissociating weak acids.

The chemical name of baking soda, a base that releases carbon dioxide with acids, used in baking and neutralisation.

The reaction of an acid with a base giving salt and water — hydrogen ions joining hydroxide ions to form water; exothermic.

A compound of a metal ion (or ammonium ion) with an acid anion, e.g. sodium chloride, copper(II) sulfate.

A medicine containing mild bases (magnesium or aluminium hydroxide) that neutralises gastric acid and relieves pain.

Adding one solution dropwise to another until the indicator shows exact neutralisation, allowing concentrations to be calculated.

A solution of accurately known concentration, the reference of a titration.

The moment the indicator just changes colour, showing the two solutions have reacted exactly.

Moles of solute per cubic decimetre of solution, in mol dm⁻³.

A long graduated tube with a tap for delivering and reading accurate volumes, holding the standard solution in titration.

A salt that dissolves in water, e.g. sodium, potassium and nitrate salts, usually made from acid plus base then crystallised.

The solid formed when solutions are mixed; insoluble salts are made by precipitation and collected by filtering.

Fuels formed from ancient remains over geological time — coal, petroleum and natural gas; non-renewable.

A compound of carbon and hydrogen only, also called a carbon-hydrogen compound; the stuff of petroleum.

Separating mixture components by their different boiling points in a fractionating column; a physical change.

A group of hydrocarbons of similar boiling range from distillation, e.g. petrol, diesel, bitumen.

A saturated hydrocarbon with only single bonds, general formula CₙH₂ₙ₊₂, e.g. methane, butane.

An unsaturated hydrocarbon with one C=C double bond, general formula CₙH₂ₙ, e.g. ethene, propene.

A hydrocarbon whose carbons are joined only by single bonds, carrying the maximum number of hydrogens.

An orange solution of bromine, rapidly decolourised by alkenes — the test for unsaturation.

Burning with ample oxygen, converting a hydrocarbon fully to carbon dioxide and water with maximum energy.

Burning short of oxygen, giving toxic carbon monoxide and soot with less energy released.