OCR GCSE Chemistry A key terms

The very small, positively charged central region of an atom, containing protons and neutrons and almost all the atom's mass.

The visible result of a test, such as a colour change, precipitate or relighting splint, recorded before drawing a conclusion.

A tenfold difference in size between quantities; two orders of magnitude means a hundredfold difference.

A naturally occurring material containing a metal or metal compound from which the metal can be extracted.

A compound based on carbon atoms, usually with carbon bonded to hydrogen and sometimes to other elements.

The pencil line on which samples are placed before the chromatogram is developed.

The highest occupied electron energy level in an atom; its electrons are involved in chemical reactions and bonding.

The highest occupied electron shell of an atom; its electrons are principally involved in chemical reactions and bonding.

An electron in the highest occupied energy level of an atom; these electrons take part in bonding.

The electrons in an atom's highest occupied energy level, which take part in covalent bonding.

The energy transferred overall when a chemical reaction takes place; in a bond-energy calculation, it is the energy needed to break bonds minus the energy released when new bonds form.

A reaction in which a substance gains oxygen; when a metal forms an oxide, the metal is oxidised.

A compound containing oxygen and at least one other element.

A group of gases, including nitrogen monoxide and nitrogen dioxide, formed when nitrogen and oxygen react at high temperatures.

A substance that causes another substance to lose electrons and is itself reduced by gaining electrons.

A gas made of molecules containing two oxygen atoms; it is released during photosynthesis and makes up about one-fifth of today's atmosphere.

An error in reading a scale caused by viewing it from an angle rather than directly at the level of the reading.

A way of explaining matter as particles, such as atoms and molecules, which can move and be rearranged.

Tiny particles suspended in air, such as soot from burning fuels.

A proportion expressed as a number out of 100.

The actual yield expressed as a percentage of the theoretical yield.

A horizontal row of the Periodic Table.

A repeating pattern in the physical and chemical properties of elements when they are placed in an appropriate order.

An organised arrangement of the elements in which elements with recurring chemical properties occur in the same columns.

Polyethylene terephthalate, a polymer used to make many drinks bottles and polyester fibres.

The industry that uses chemicals obtained from crude oil and natural gas to manufacture other chemicals and materials.

A numerical measure of how acidic, neutral or alkaline a solution is; acidic solutions have values below 7, a neutral solution has pH 7 and alkaline solutions have values above 7.