OCR GCSE Chemistry A key terms

The power in an expression such as $10^n$; it shows how many places the digits change in place value.

A substance that changes colour according to the pH of a solution.

A sphere that does not change shape when forces act on it.

An electrode, such as graphite, that conducts electricity without being intended as a reactant in the cell.

A conclusion drawn from evidence rather than observed directly.

Electromagnetic radiation emitted strongly by the warm Earth’s surface and absorbed by greenhouse gases.

The rate of reaction at the beginning of a reaction, found from the gradient of a tangent at time zero.

The rate at one particular moment, represented by the gradient of a tangent to a curve.

The use of scientific instruments to detect, identify or measure substances from a recorded signal.

The brightness of light measured at a particular wavelength.

The boundary where two liquids meet. In the nylon demonstration, the polymer first appears where the two solutions touch.

An attraction between separate molecules; it is weaker than the covalent bonds within those molecules.

Attractive forces between separate molecules, rather than bonds between atoms within a molecule.

The total energy stored by the particles of a substance through their movement and their positions relative to one another.

An estimate of a value between measured data points.

A relationship in which one quantity changes by the opposite factor to another, so their product stays constant.

An operation that reverses another operation, such as subtraction reversing addition and division reversing multiplication.

An atom or group of atoms with an electrical charge, formed when electrons are lost or gained.

A strong electrostatic attraction between oppositely charged ions.

The electrical property of an ion, written as a superscript with a magnitude and a positive or negative sign, such as $2+$ or $1-$.

A substance made from oppositely charged ions held together by electrostatic attraction.

An equation showing the particles that take part in a reaction, without unchanged spectator ions.

One of two or more atoms of the same element that have the same number of protons but different numbers of neutrons.

A regular, repeating arrangement of particles extending throughout a solid.

The principle that mass is not created or destroyed, so the total mass of all reactants equals the total mass of all products.

A solution containing metal compounds released from an ore during leaching.

Digits written before the first non-zero digit to position the decimal point; they do not count as significant figures.