Aqa As Chemistry Definitions Unit 1

Front 1

Mass number

Back 1

Mass number = number of protons + neutrons (in the nucleus/atom)

Front 2

Relative atomic mass

Back 2

Average/mean mass of an atom divided by 1/12 the mass of an atom of 12C

Front 3

First ionisation energy

Back 3

The energy required to remove 1 (mole) electron(s) from 1 (mole) gaseous atom(s), forming 1 (mole) ion(s) with a single positive charge.

Front 4

Dynamic equilibrium

Back 4

Rate of forward reaction = rate of backward reaction (1) concentrations of reactants and products remain constant. (1)

Front 5

Empirical formula

Back 5

A formula which gives the simplest whole number ratio of atoms of each element in a compound.

Front 6

Covalent bond

Back 6

A shared pair of electrons.

Front 7

Co-ordinate (dative) bond

Back 7

A covalent bond in which the shared pair of electrons are provided by just one of the bonded atoms.

Front 8

Electronegativity

Back 8

The power of an atom to attract electrons towards itself in a covalent bond.

Front 9

Atomic radius

Back 9

The distance from the centre of the nucleus to the outer electrons of an atom.

Front 10

Structural isomerism

Back 10

Compound which have the same molecular formula but different structures/different structural formulae/different displayed formulae.

Front 11

Homologous Series

Back 11

A family of organic molecules which all contain the same functional group, but have an increasing number of carbon atoms.

Front 12

Activation Energy

Back 12

Minimum energy (1) to start a reaction (1)

Front 13

Catalyst

Back 13

Speeds up a reaction but is chemically unchanged at the end (1)

Front 14

Stereoisomers

Back 14

Compounds with the same structural formula (1) but a different arrangement of atoms in space (1)

Front 15

Hess' Law

Back 15

Enthalpy change is independent of the route taken

Front 16

Nucleophile

Back 16

Electron pair donor.

Front 17

Enthalpy Change

Back 17

Change in heat energy under a constant pressure.

Front 18

Standard Enthalpy Change of Formation

Back 18

The enthalpy change when one mole of a substance is formed from its constituent elements under standard conditions, with all reactants and products in their standard states.

Front 19

Standard Enthalpy Change of Combustion

Back 19

The enthalpy change when one mole of a substance is completely burned in Oxygen under standard conditions, with all reactants and products in their standard states.

Front 20

Bond Enthalpy

Back 20

Enthalpy change to break one mole of covalent bonds in the gaseous state.

Front 21

Mean Bond Enthalpy

Back 21

Enthalpy change to break one mole of covalent bonds in the gas phase average over a range of compounds.

Front 22

Polymerisation

Back 22

The joining together of monomers (1) to form long chains (1)

Front 23

Reduction/Oxidation

Back 23

Reduction = gain, Oxidation = loss

Front 24

Reducing/Oxidising Agents

Back 24

RA = electron donors, OA = electron acceptors

Front 25

Rate of Reaction

Back 25

The change in concentration of a substance in unit time.

Front 26

Le Chatelier’s principle

Back 26

If a system in equilibrium is disturbed, equilibrium will shift to oppose that change.

Front 27

Disproportination

Back 27

A reaction in which the same species is simultaneously oxidised and reduced.

Front 28

Avogadro's Constant

Back 28

Number of particles present in a mole (6.02 x 1023 mol-1).

Front 29

Percentage Atom Economy %

Back 29

mass of desired product (Mr)/ total mass of reactants x 100 - include coefficients.

Front 30

Electrophile

Back 30

An electron-deficient atom/ion.

Front 31

Free Radical

Back 31

A chemical species with an unpaired electron.