Chemistry Definitions

Front 1

Atomic number (proton number)

Back 1

The number of protons in the nucleus of an atom.

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Mass number (nucleon number)

Back 2

The number of protons plus neutrons in the nucleus of an atom.

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Isotopes

Back 3

Atoms of the same element with a different number of neutrons

Front 4

Relative isotopic mass

Back 4

The mass of an atom of an isotope compared with 1/12 of the mass of an atom of carbon-12.

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Relative atomic mass

Back 5

The weighted mean mass of an atom of an element compared with 1/12 of the mass of an atom of carbon-12.

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Acid

Back 6

A proton (H+) donor

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Base

Back 7

A proton (H+) acceptor

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Strong acid

Back 8

Completely dissociates into its ions in aqueous solution

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Weak acid

Back 9

Partially dissociates into its ions in aqueous solution

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Alkali

Back 10

Base that dissolves in water and releases OH- ions in aqueous solution

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Salt

Back 11

A salt is produced when the H+ ion of an acid is replaced by a metal ion or NH4+.

Front 12

Atomic orbital

Back 12

A region within an atom that can hold up to two electrons with opposite spins.

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First ionisation energy

Back 13

The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions

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Successive ionisation energies

Back 14

A measure of the energy required to remove each electron in turn.

Front 15

Mole

Back 15

The amount of substance containing as many particles as there are carbon atoms in exactly 12g of carbon 12.

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Molar mass

Back 16

The mass, in grams, per mole of a substance.

Units- gmol-1

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Mass (g) =

Back 17

Moles x Molar mass (RFM)

Front 18

The Avogadro constant

Back 18

The number of particles in 1 mole of any substance is equal to 6.02 x10^23

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Hydrated

Back 19

When water of crystallisation is present in a crystal compound.

Front 20

Anhydrous

Back 20

When all the waters of crystallisation have been removed from a compound.

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Water of crystalliation

Back 21

The water present in a compound giving the compound a crystalline appearance ( the x.H2O term)

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Ionic bonding

Back 22

The electrostatic attraction between oppositely charged ions

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Covalent bonding

Back 23

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

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Dative covalent (coordinate) bonding

Back 24

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms, where only one of the atoms supplies both of the electrons shared.

Front 25

Average bond enthalpy

Back 25

Average bond enthalpy can be used as a measurement of covalent bond strength.

Front 26

Molar gas volume

Back 26

Molar gas volume at r.t.p 24.0 dm3 mol-1

1 mol of any gas = 24.0dm3 (24,000cm3)

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Ideal gas equation

Back 27

p V = n R T

Front 28

Reacting moles in solution equation

Back 28

Moles = concentration x volume

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The shape of a molecular ion is determined by...

Back 29

-The number and type of electron pairs in the outer shell of the central atom.

Electron pairs repel other electron pairs, as far apart as possible.

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Electronegativity

Back 30

The ability of an atom to attract the bonding electrons towards itself in a covalent bond.

Front 31

Metallic bonding

Back 31

The attraction of a lattice of positive ions to a 'sea' of delocalised electrons

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Ionic compounds

Back 32

The solid structure of a giant ionic lattice results from the regular arrangement of oppositely charged ions strongly attracted in all directions

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Simple covalent compounds

Back 33

Structures made up of small, simple molecules with weak forces of attraction between the molecules.

Front 34

Giant covalent structures

Back 34

Soldis which are networks of atoms bonded together by strong covalent bonds.

Front 35

Oxidation number/state

Back 35

A measure of the number of electrons that the atom uses to bond with atoms of another element.

Front 36

Redox

Back 36

A reaction where both oxidation and reduction take place

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Oxidation

Back 37

The loss of electrons/ increase in oxidation number

Front 38

Reduction

Back 38

The gain of electrons/ decrease in oxidation number

Front 39

Hydrocarbons

Back 39

A compound that contains only carbon and hydrogen

Front 40

Homologous series

Back 40

A family of compounds containing the same functional group but with each successive member of the series differing by a CH2 group

Front 41

Functional group

Back 41

An atom/group responsible for the characteristic reactions of the compound

Front 42

Aromatic compounds

Back 42

Compounds containing a benzene ring with formula C6H6

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Aliphatic compounds

Back 43

Compounds of hydrogen and carbon joined together in straight chains, branched chains and non- aromatic rings.

Front 44

Alicyclic compounds

Back 44

Aliphatic compounds arranged in non-aromatic rings, with or without side chains.

Front 45

General formula

Back 45

The simplest algebraic formula for any member of a homologous series

Front 46

Displayed formula

Back 46

This shows all the the bonds and how all the atoms are joined together in the structure.

Front 47

Structural formula

Back 47

This shows minimum detail required for the arrangement of atoms in a molecule. The carboxyl group is represented as COOH and the ester group as COO

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Skeletal formula

Back 48

This 'hides' ever carbn atom and any H atom which is directly attached to a C atom. This leaves just the carbon backbone and any functional groups

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Structural isomers

Back 49

Molecules with the same molecular formula but a different structural formula

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Homolytic fission

Back 50

The breaking of a covalent bond where one electron from the bonding pair goes to each atom to form 2 radicals

Front 51

Heterolytic fission

Back 51

The breaking of a covalent bond where both electrons from the bonding pair go the the same atom to form 2 ions

Front 52

Addition reaction

Back 52

Two molecules react to make one product. One molecule adds across the double bond of an unsaturated molecule to make a saturated molecule

Front 53

Substitution reaction

Back 53

A reaction where an atom/group is replaced by another atom/group

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Elimination reaction

Back 54

An atom/group is removed from a saturated molecule to make an unsaturated molecule

Front 55

Oxidation reaction

Back 55

Oxygen is added and/or hydrogen is removed from a molecule

Front 56

Condensation reaction

Back 56

A reaction where a H2O molecule is lost when two molecules join together

Front 57

Alkanes

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Saturated hydrocarbons

Front 58

C-C and C-H bonds

Back 58

They're made up of a sigma bond

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Sigma bond

Back 59

Formed between 2 carbon atoms or a carbon and hydrogen atom by a single axial overlap of orbitals. This allows free rotation of the sigma bond

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Radical substitution

Back 60

This is a substitution type reaction because a H atom in the alkane molecule is replaced by a halogen atom.

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Radical

Back 61

A species with an unpaired electron

Front 62

Percentage yield

Back 62

A measure of the efficiency of converting reactants into products

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Yield

Back 63

The mass of a product obtained from a reaction

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% yield equation

Back 64

(actual mass of product/ theoretical mass of product) x 100

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Second % yield equation

Back 65

(actual mol of product/ theoretical mol of product) x 100

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Atom economy

Back 66

A measure of how much of the total mass of reactants is converted into the desired product

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Atom economy equation

Back 67

(Mr of desired product/Mr of total product) x 100

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What forms a carbon double bond?

Back 68

A sigma and a pi bond

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Pi bond

Back 69

Formed by the double, sideways overlap of p orbitals above and below the bonding carbon atoms

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Stereoisomers

Back 70

Compounds with the same structural and molecular formula but with a different arrangement of the atoms in space

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Criteria for E/Z isomerism

Back 71

Must have a C-C double bond because this can't rotate

Each carbon atom of the C-C double bond must have 2 different groups attached to it

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Criteria for cis/trans stereoisomerism

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Must have a C-C double bond because this can't rotate.

Each carbon of the C-C must have 2 different groups attached to it.

Two groups must be the same, one on each C of the C-C double bond

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Z (cis) isomer

Back 73

Has the same groups on the same side

Front 74

E (trans) isomer

Back 74

Has the same groups diagonally opposite

Front 75

Chemical test for the alkene functional group

Back 75

Add bromine. bromine water and shake.

If bromine is decolourised(from orange to colourless) the compound is an alkene.

If the bromine is not decolourised, the compound is not alkene.

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Electrophile

Back 76

An electron pair receptor

Front 77

Curly arrow model

Back 77

A curly arrow shows the movement of an electron pair, to either make or break a covalent bond

Front 78

Enthalpy change

Back 78

The amount of heat released (or absorbed) by a chemical reaction, carried out at constant pressure. Units: kJ mol-1

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Exothermic reaction

Back 79

A reaction where heat energy is released to the surroundings. ∆H is negative.

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Endothermic reaction

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A reaction where heat energy is absorbed from the surroundings. ∆H is positive.

Front 81

Average bond enthalpy ∆HθE

Back 81

The average enthalpy change when 1 mole of gaseous bonds are broken by homolytic fission

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Standard conditions

Back 82

Temperature-25 degrees c (298K)

Pressure- 1atm (100kPa)

Solutions must have a concentration = 1.0 mol dm-3

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Standard enthalpy change of a reaction ∆HθR

Back 83

The enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states.

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Standard enthalpy of neutralisation ∆Hnθ

Back 84

The enthalpy change that accompanies the neutralisation of an aqueous acid by an aqueous base to form 1 mole of H2O (l) under standard conditions.

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Standard enthalpy change of formation ∆HθF

Back 85

The enthalpy change when 1 mole of a compound is formed form its constituent elements in their standard states, under standard conditions.

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Standard enthalpy change of combustion ∆HθC

Back 86

The enthalpy change when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard states.

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Hess's law

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The enthalpy change of a reaction depends only on the initial and final states and is independent of the route taken.

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Rate of reaction

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The rate of a chemical reaction is the change in concentration of a reactant or a product per unit time.

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Activation energy

Back 89

The minimum energy required to start a reaction by the breaking of bonds in the reactants

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What does a catalyst do?

Back 90

It increases the rate of reaction and is not consumed(used up) by the overall reaction.

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Heterogeneous catalysis

Back 91

Catalysis of a reaction in which the catalyst has a different physical state from the reactants( frequently, reactants are gases while the catalyst is a solid)

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Homogeneous catalysis

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Catalysis of a reaction in which the catalyst and the reactants are in the same physical state( frequently the aqueous or gas state)

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How does a catalyst work?

Back 93

A catalyst the increases rate of reaction by providing a different pathway (mechanism) for the reaction which has a lower activation energy

Front 94

Reaction taking place on a catalytic converter

Back 94

2NO(g)+2CO(g)-->N2(g)+2CO2(g)

Front 95

Adsorption

Back 95

The CO and NO molecules adsorb to the catalyst surface, The bonds within the molecules weaken. The activation energy is lowered

Front 96

Chemical reaction

Back 96

Bonds broken in the CO and NO reactant molecules.

New bonds formed to make CO2 and N2 products

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Desorption

Back 97

The CO2 and N2 products desorb from the catalyst surface.

Front 98

Oxidising power of a halogen

Back 98

A measure of the strength with which a halogen atom is able to attract and capture an electron to form a halide ion

Front 99

Displacement reaction

Back 99

A reaction in which a more reactive element displaces a less reactive element from an aqueous solution of its halide ions

Front 100

Nucleophile

Back 100

An electron pair donor

Front 101

Disproportionation reaction

Back 101

A reaction in which the same element is both oxidised and reduced

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Dehydration

Back 102

A reaction where a H2O molecule is removed from a saturated to an unsaturated molecule.

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Reversible reaction

Back 103

A reaction mad up of a forward reaction and a reverse reaction.

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Dynamic equilibrium

Back 104

This exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction.

Front 105

Characteristics of dynamic equilbrium

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Rate of forwards=rate of reverse

Closed system

Concentrations remain constant

Macroscopic properties do not change

Front 106

Le Chatelier's principle

Back 106

When a system in dynamic equilibrium is subjected to a change, the position of equilibrium will shift to minimise the change

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Curly arrow

Back 107

The movement of an electron pair, showing either heterolytic fission of, or formation of, a covalent bond

Front 108

Hydrolysis

Back 108

A chemical reaction involving water, or an aqueous solution, which causes the breaking of a bond, splitting a reactant molecule into two products

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Volatility

Back 109

The ease with which a liquid turns into a gas

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Precipitate

Back 110

An insoluble solid formed when two solutions are mixed together

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Solution

Back 111

A homogeneous mixture composed of two or more substances. A solution consists of a solute and solvent.

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Solute

Back 112

The substance that is dissolved in the solvent

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Distillation

Back 113

The technique of heating a liquid to create vapour which is collected when cooled and condensed, separate from the original liquid.

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Heat under reflux

Back 114

The continuous boiling and condensing of a liquid, in a condenser, preventing loss of volatile liquids from a heated reaction vessel