chemistry

  • Absorption spectrum: A spectrum of electromagnetic radiation transmitted through a substance, showing dark lines or bands due to absorption at specific wavelengths.
  • Acid (according to Arrhenius theory): A substance which dissociates in water to provide H+ ions.
  • Acid (according to 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, characteristic of alkenes and alkynes.
  • 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; diamond, graphite, and charcoal are allotropes of carbon.
  • 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, able to react with both alkalis and acids.
  • 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 by making aluminium the anode in an electrolysis cell.
  • 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 (according to Arrhenius theory): A substance which dissociates in water to produce OH– ions.
  • Base (according to Bronsted-Lowry theory): A proton acceptor.
  • Base hydrolysis of esters (saponification): The alkaline hydrolysis of animal fat 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, defined as the amount of dissolved oxygen consumed by biochemical action in darkness at 20° C for 5 days.
  • Bond energy: The average energy required to break one mole of bonds of the same type with all reactants in the gaseous state.
  • 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 during the reaction.
  • Catalyst poison: A substance that destroys the activity of a catalyst.
  • Catalytic converter: Changes poisonous gases like carbon monoxide and nitrogen oxides in car exhausts into less harmful molecules, such as CO₂ and nitrogen.
  • 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; CFCs break down in the stratosphere and release chlorine free radicals that attack ozone.