chemistry

Absorption spectrum

A spectrum of electromagnetic radiation transmitted through a substance, showing dark lines or bands due to absorption at specific wavelengths.

Acid (Arrhenius theory)

A substance which dissociates in water to provide H+ ions.

Acid (Bronsted-Lowry theory)

A proton donor.

Acid-base indicator

Substances which change colour with pH.

Activation energy (EACT)

The minimum amount of energy which colliding molecules must have before they can react together.

Addition polymer

A polymer made by the combining together of small unsaturated molecules of the same compound.

Addition reaction

A reaction in which the double or triple bond of an unsaturated compound opens up and other atoms add on to the molecule.

Alcohols

Organic compounds in which the –OH (hydroxyl group) is bound to a saturated carbon atom.

Aldehydes

Organic compounds containing the functional group with the structure –CHO (carbonyl group).

Aliphatic hydrocarbon

Compounds containing only chains of carbon atoms.

Alkali Metals

Elements of Group 1 of the Periodic Table.

Alkanes

Hydrocarbons with only single bonds between carbon atoms.

Alkenes

Hydrocarbons with a double bond between two carbon atoms.

Alkynes

Hydrocarbons with a triple bond between two carbon atoms.

Allotropes

Different physical forms of the same element due to different arrangements of atoms.

Alloy

A mixture of metals.

Alpha particle

A high-speed, positively charged helium nucleus.

Amphoteric substance

A substance which shows both acidic and basic properties.

Anion

The ion attracted to the anode.

Anode

The positive electrode in electrolysis.

Anodising

A process that thickens the oxide layer on the surface of aluminium for corrosion protection.

Aromatic compound

Compounds containing a 6-membered ring of carbon atoms.

Atom

The smallest particle of a chemical element that can exist.

Atomic number

The number of protons characteristic of an element.

Atomic orbital

A region in space with a high probability of finding an electron.

Atomic radius

Half the distance between the nuclei of atoms of that element when bonded by a single covalent bond.

Aufbau principle

Electrons occupy the lowest available energy level.

Auto-ignition

The explosion of the petrol-air mixture in the engine before the spark is produced.

Autocatalysis

The catalysis of a reaction by one of the products of that reaction.

Avogadro constant

The number of particles in a mole of a substance, approximately 6×10²³.

Avogadro’s law

States that equal volumes of gases under the same conditions of temperature and pressure contain equal numbers of molecules.

Balmer Series

The visible line spectrum of Hydrogen.

Base (Arrhenius theory)

A substance which dissociates in water to produce OH– ions.

Base (Bronsted-Lowry theory)

A proton acceptor.

Base hydrolysis of esters (saponification)

The alkaline hydrolysis of animal or vegetable fats to prepare soap.

Beta particle

A high-speed electron emitted from the nucleus of an unstable atom.

Biochemical oxygen demand (BOD)

A measure of organic pollution in water.

Bond energy

The average energy required to break one mole of bonds of the same type.

Boyle’s law

For a fixed mass of gas kept at constant temperature, the volume is inversely proportional to the pressure.

Carbonium ion

An unstable positive carbon intermediate.

Carboxylic acid

An organic compound containing a carboxyl group (-COOH).

Catalyst

A substance that alters the rate of a chemical reaction without being used up.

Catalyst poison

A substance that destroys the activity of a catalyst.

Catalytic converter

Changes poisonous gases in car exhausts into less harmful molecules.

Catalytic cracking

The breaking down of long-chain hydrocarbons into short-chain molecules using heat and catalysts.

Cathode

The negative electrode in electrolysis.

Cation

The ion which is attracted to the cathode.

Charles’s law

For a fixed mass of gas kept at constant pressure, the volume is directly proportional to the absolute temperature.

Chemical equilibrium (dynamic)

A state where the rate of the forward reaction equals the rate of the reverse reaction.

Chlorofluorocarbons (CFCs)

Substances that damage ozone in the atmosphere.