AS Chemistry Important Terms & Definitions


Acids are chemical species that donate protons/hydrogen ions. Strong acids completely dissociate into ions in aqueous solutions. Weak acids only dissociate partially in aqueous solutions.

Activation energy is the minimum amount of energy needed before a reaction can occur.

Addition reaction is the joining of two molecules to form a single product molecule.

Addition Polymers are polymers formed by repeated addition reactions.

Relative Atomic Mass is the weighted average of the masses of an element's isotopes relative to one twelth of the mass of a Carbon 12 atom.

Atomic Number is the number of protons in the nucleus of each atom in an element.

A Base is a chemical species which accept protons/hydrogen ions.

Bond enthalpy is the amount of energy required to break one mole of a bond in a gaseous molecule

Catalysts are substances that increase the rate of chemical reaction by providing an alternative pathway of lower activation energy, but which are left unchanged by the reaction.

Chiral centres (also known as asymmetric carbon atoms) is an atom in a molecule which is bonded to four different chemical groups, giving rise to optical isomerism.

Acid base Conjugate pairs are two molecules or ions that differ by one hydrogen ion

Dative or co-ordinate covalent bonds is a covalent bond where both electrons come from the same atom.

A Dynamic equilibrium occurs when, for a reversible reaction, the forward and reverse reactions occur at the same rate, so there is no change in net concentration.  This must occur in a closed system

Electronegativity is the ability of an atom to attract bonding electrons in a covalent bond.

An electrophile is an atom or group of atoms which is attracted to an electron-rich centre or atom where it accepts a pair of electrons to form a covalent bond.

Empirical formula shows the simplest whole number ratio of elements in a compound.

An enantiomer is a molecule with a chiral centre which can exist in two forms (two optical isomers).  They can be distinguished by the direction in which they rotate a plane of polarised light or by certain enzyme reactions.

Relative Formula Mass is the sum of the atomic masses in a compound, giving the mass of the compound relative to one twelth of the mass of a carbon-12 atom.

A free radical is an atom or group of atoms with an unpaired electron.

The Functional


Clara Werkmeister


what about *rate of reaction*?