Aqa As Physical Chemistry

Front 1

Nucleus

Back 1

The tiny, positively charged centre of an atom composed of protons and neutrons.

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Nucleons

Back 2

Protons and neutrons—the subatomic particles found in the nuclei of atoms.

Front 3

Strong nuclear force

Back 3

The force that holds protons and neutrons together within the nucleus of an atom.

Front 4

Electrostatic forces

Back 4

The forces of attraction and repulsion between electrically charged particles.

Front 5

Proton number, Z

Back 5

The number of protons in the nucleus of an atom; the same as the atomic number.

Front 6

Relative atomic mass, Ar

Back 6

(Average mass of an atom)÷(1/12 the mass of 1 atom of carbon-12)

Front 7

Molecular ion

Back 7

In mass spectrometry this is a molecule of the sample which has been ionised but which has not broken up during its flight through the instrument.

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Atomic orbital

Back 8

A region of space around an atomic nucleus where there is a high probability of finding an electron.

Front 9

Ionisation energy

Back 9

The energy required to remove a mole of electrons from a mole of gaseous atoms or ions.

Front 10

Relative molecular mass, Mr

Back 10

(Average mass of a molecule)÷(1/12 the mass of 1 atom of carbon-12)

Front 11

Relative formula mass, Mr

Back 11

Same as molecular mass but for ionic compounds.

Front 12

The Avogadro constant / Avogadro's number

Back 12

The total number of particles in a mole of substance. 6.022 × 10^23

Front 13

Mole

Back 13

A quantity of a substance that contains the Avogadro number of particles.

Front 14

Empirical formula

Back 14

The simplest whole number ratio of atoms of each element in a compound.

Front 15

Molecular formula

Back 15

A formula that tells us the actual numbers of atoms of each different element that make up a molecule of a compound.

Front 16

Stoichiometry

Back 16

Describes the simple whole number ratios in which chemical species react.

Front 17

Spectator ions

Back 17

Ions that are unchanged during a chemical reaction, that is, they take no part in the reaction.

Front 18

Atom economy

Back 18

% = (mass of desired product) ÷ (total mass of reactants) then × 100

Front 19

Ionic bonding

Back 19

Describes a chemical bond in which an electron or electrons are transferred from one atom to another, resulting in the formation of oppositely charged ions with electrostatic forces of attraction between them.

Front 20

Lattice

Back 20

A regular three-dimensional arrangement of atoms, ions or molecules.

Front 21

Covalent bonding

Back 21

Describes a chemical bond in which a pair of electrons are shared between two atoms.

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Co-ordinate bonding / Dative covalent bonding

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Covalent bonding in which both the electrons in the bond come from one of the atoms in the bond.

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Lone pair

Back 23

A pair of electrons in the outer shell of an atom that is not involved in bonding.

Front 24

Metallic bonding

Back 24

Describes a chemical bond in which outer are delocalised within the lattice of metal ions.

Front 25

Delocalised

Back 25

Describes electrons that are spread over several atoms and help to bond then together.

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Electronegativity

Back 26

The power of an atom to attract the electron density in a covalent bond towards itself.

Front 27

Electron density

Back 27

The probability of electrons being found in a particular volume of space.

Front 28

Polar molecule

Back 28

A molecule in which the charge is not symmetrically distributed so that one area is slightly positively charged and another slightly negatively charged.

Front 29

van der Waals force

Back 29

A type of intermolecular force of attraction that is caused by instantaneous dipoles and acts between all atoms and molecules.

Front 30

Dipole-dipole force

Back 30

An intermolecular force that results from the attraction between molecules with permanent dipoles.

Front 31

Hydrogen bonding

Back 31

A type of intermolecular force in which a delta-plus hydrogen atom interacts with a more electronegative atom with a delta-minus charge.

Front 32

Electron pair repulsion theory

Back 32

Explains the shapes of simple molecules by assuming that pairs of electrons around a central atom repel each other and thus take up positions as far away as possible from each other in space.

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Exothermic

Back 33

A reaction in which heat is given out as reactants change to products; the temperature thus rises.

Front 34

Endothermic

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A reaction in which heat is taken in as the reactants change to products; the temperature thus drops.

Front 35

Enthalpy change

Back 35

A measure of heat energy given out or taken in when a chemical or physical change occurs at constant pressure.

Front 36

Standard molar enthalpy of formation, ∆fH°

Back 36

The enthalpy change when 1 mole of substance is formed from its constituent elements under standard conditions, all reactants and products being in their standard states.

Front 37

Standard molar enthalpy of combustion, ∆cH°

Back 37

The enthalpy change when 1 mole of substance is completely burnt in oxygen under standard conditions, all reactants and products being in their standard states.

Front 38

Specific heat capacity

Back 38

The amount of heat needed to raise the temperature of 1g of a substance by 1K

Front 39

Calorimeter

Back 39

An instrument for measuring the heat changes that accompany chemical reactions.

Front 40

Thermochemical cycle

Back 40

A sequence of chemical reactions (with their enthalpy changes) that convert a reactant into a product.

Front 41

Hess's law

Back 41

States that enthalpy change for a chemical reaction is the same, whatever route is taken from reactants to products

Front 42

Enthalpy diagrams

Back 42

Diagrams in which the enthalpies of the reactants and products are plotted on a vertical scale to show their relative levels.

Front 43

Bond dissociation enthalpy

Back 43

The enthalpy change required to break a covalent bond with all species in the gaseous state.

Front 44

Mean bond enthalpy

Back 44

The average value of the bond dissociation enthalpy for a given type of bond, taken from a range of different compounds.

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Activation energy

Back 45

The minimum energy that a particle needs in order to react; the energy difference between the reactants and the transition state.

Front 46

Transition state

Back 46

The species that exists at the top of the curve of an enthalpy diagram.

Front 47

Maxwell-Boltzmann distribution

Back 47

The distribution of energies (and therefore speeds) of the molecules in a fluid.

Front 48

Catalyst

Back 48

A substance that alters the rate of a chemical reaction but is not used up in the reaction.

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Equilibrium mixture

Back 49

The mixture of reactants and products formed when a reversible reaction is allowed to proceed in a closed container until no further change occurs. The forward and backward reactions are still proceeding but at the same rate.

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Le Châtelier's Principle

Back 50

If a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to reduce the disturbance. (Will shift to oppose the change.)

Front 51

Chemical feedstock

Back 51

The starting materials in an industrial chemical process.

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Oxidation

Back 52

A reaction in which an atom or group of atoms loses electrons.

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Oxidising agent

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A reagent that oxidises (removes electrons from) another species. An electron acceptor.

Front 54

Reduction

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A reaction in which an atom or a group of atoms gains electrons.

Front 55

Reducing agent

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A reagent that reduces (adds electrons to) another species. An electron donor.

Front 56

Redox reaction

Back 56

A reaction in which electrons are transferred from one species to another.

Front 57

Spectator ions

Back 57

Ions that are unchanged during a chemical reaction, that is, they take no part in the reaction.

Front 58

Half equation

Back 58

An equation for a redox reaction which considers just one of the species involved and shows explicitly the electrons transferred to our from it.

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Oxidation states

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The number of electrons lost or gained by an atom in a compound compared to the uncombined atom. Aka oxidation number.