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AS OCR Chemistry Definitions > Definitions > Flashcards

Definitions Flashcards

1
Q

Acid

A

A species that is a proton donor

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1
Q

Activation Energy

A

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

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1
Q

Addition Polymer

A

A very long molecular chain formed by repeated addition reactions of many unsaturated alkene molecules (monomers)

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1
Q

Addition Polymerisation

A

The process in which unsaturated alkene molecules (monomers) add onto a growing polymer chain one at a time to form a very long saturated molecular chain (the addition polymer).

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1
Q

Addition Reaction

A

A reaction in which a reactant is added to an unsaturated molecule to make a saturated molecule.

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1
Q

Adsorption

A

The process that occurs when a gas, liquid or solute is held to the surface of a solid or, more rarely, a liquid.

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1
Q

1st Ionisation Energy

A

The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions with a single positive (1+) charge

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1
Q

2nd Ionisation Energy

A

The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions with a doublepositive (2+) charge

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2
Q

Alicyclic hydrocarbon

A

A hydrocarbon with carbon atoms joined together in a ring structure

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3
Q

Aliphatic Hydrocarbon

A

A hydrocarbon with carbon atoms joined together in a straight or branched chains

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4
Q

Alkali

A

A type of base that dissoves in water forming hydroxide ions OH- (aq) ions

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5
Q

Alkanes

A

The homologous series with the general formula CnH2n+2

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7
Q

Alkyl group

A

An alkane with a hydrogen atom removed eg. CH3, C2H5. Alkyl groups are often shown as ‘R’

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8
Q

Amount of Substance

A

Quantity whose unit is the mole. Chemists use the “amount of substance” as a means of counting atoms

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9
Q

Anhydrous

A

A substance that contains no water molecules

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10
Q

Anion

A

Negatively charged ion

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11
Q

Atom Economy

A
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12
Q

Atomic Orbital

A

A region of space in which up to two electrons can be found with opposite spins

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12
Q

Atomic (proton) number

A

The number of protons in the nucleus of the atom. The same as the number of electrons surrounding a neutrally charged atom of the element.

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12
Q

Average bond enthalpy

A

The average enthalpy change that takes place when breaking by homolytic fission 1 mole of a given type of bond in the molecules of a gaseous species

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13
Q

Avogadro Constant NA

A

The number of atoms per mole of the carbon-12 isotope (6.02 x10^23)

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13
Q

Base

A

A species that is proton acceptor

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13
Q

Biodegradable material

A

A substance that is broken down naturally in the environment by living organisms

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14
Q

Bolzmann Distribution

A

The distribution of energies of molecules at a particular temperature, usually shown as a graph.

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15
Q

Bond enthalpy

A

The enthalpy change that takes place when breaking by homolytic fission 1 mole of a given bond in the molecule of a gaseous species

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16
Q

Carbanion

A

An organic ion in which a carbon atom has a negative charge

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17
Q

Carbocation

A

An organic ion in which a carbon atom has a positive charge (Br2 mechanism)

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18
Q

Catalyst

A

A substance that increases the rate of a chemical reaction without being used up in the process.

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20
Q

Cation

A

A positively charged ion

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21
Q

Cis-trans isomerism

A

A special type of E/Z isomerism in which there is a non-hydrogen group and a hydrogen atom on each C of a C=C double bond. Cis –> H atoms are on the same side (like the Z) Trans –> H atoms are on different sides (like the E)

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23
Q

Compound

A

A substance formed from two or more chemically bonded elements in a fixed ratio, usually shown by a chemical formula

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24
Q

Concentration

A

The amount of solute, in mole, per 1 dm^3 (1000cm^3) of solution

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25
Q

Covalent Bond

A

A bond formed by a shared pair of electrons

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25
Q

Cracking

A

The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-chained alkanes and alkenes.

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26
Q

Curly Arrow

A

A symbol used in reaction mechanisms to show the movement of a pair of electrons in the breaking or formation of a covalent bond

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27
Q

Dative Covalent Bond / Co-ordinate bond

A

A shared pair of electrons which has been provided by one of the bonding atoms only.

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28
Q

Dehydration

A

An elimination reaction in which water is removed from a saturated molecule to make an unsaturated molecule

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29
Q

Delocalised electrons

A

Electrons that are shared between more than two atoms esp. found in metallic bonds

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30
Q

Displacement reactions

A

A reaction in which a more reactive element displaces a less reactive element from an aqueous solution of the latter’s ions

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31
Q

Displayed formula

A

A formula showing the relative positioning of all the atoms in a molecule and the bonds between them

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32
Q

Disproportionation

A

A special type of redox in which the same species is simultaneously oxidised and reduced at the same time.

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32
Q

Dynamic equilibrium

A

The equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the backwards reaction

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34
Q

E/Z isomerism

A

A type of stereoisomerism in which different groups attached to each carbon of the C=C double bond may be arranged differently in space because of restricted rotation of the C=C double bond.

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35
Q

Electron configuration

A

The arrangement of electrons in an atom

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36
Q

Electron shielding

A

The repulsion between electrons in different inner shells. Shielding reduces the net attractive force from the positive nucleus on the outer-shell electrons

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37
Q

Electronegativity

A

The measure of the attraction of a bonded atoms for the pair of electrons in a covalent bond

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38
Q

Electrophile

A

An atom (or group of atoms) that is attracted to an electron-rich centre where it accepts a pair of electrons to form a new covalent bond

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39
Q

Electrophilic addition

A

A type of addition reaction in which an electrophile is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond

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40
Q

Elimination reaction

A

The removal of a molecule from a saturated molecule to make an unsaturated molecule

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42
Q

Empirical formula

A

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

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43
Q

Endothermic Enthalpy Profile Diagram

A
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44
Q

Endothermic reaction

A

A reaction in which the enthalpy of products is greater than the enthalpy of the reactants, resulting in heat being taken in from the surrounding (ΔH = +ve)

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45
Q

Enthalpy cycle

A

A diagram showing alternative routes between reactants and products which allows the indirect determination of an enthalpy change from other known enthalpy changes using Hess’ Law

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46
Q

Enthalpy Formula

A

-q/mol

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47
Q

Enthalpy profile diagram

A

A diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products

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48
Q

Enthalpy, H

A

The heat content that is stored in a chemical system

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50
Q

Esterification

A

The reaction of an alcohol with a carboxylic acid to produce an ester and water

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50
Q

Ethene and Bromine Mechanism

A
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52
Q

Exothermic reaction

A

A reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in a heat loss to the surroundings (ΔH = -ve)

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52
Q

Exothermic Enthalpy Profile Diagram

A
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54
Q

Fractional Distillation

A

The separation of the components in a liquid mixture into fractions which differ in boiling point (and hence chemical composition) by means of distillation (evaporation and condensation) by use of a fractionating column

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55
Q

Fragmentation

A

The process in mass spectrometry that causes a positive ion to split into pieces, one of which is a positive fragment ion

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55
Q

Functional group

A

The part of the organic molecule responsible for its chemical reactions

56
Q

General formula

A

The simplest algebraic formula for a member of a homologous series. Eg. CnH2n+2

57
Q

Giant covalent lattice

A

A 3D structure of oppositely charged ions bonded together by strong covalent bonds

58
Q

Giant ionic lattice

A

A 3D structure of oppositely charged ions bonded together by strong ionic bonds (electrostatic forces of attraction)

59
Q

Giant metallic lattice

A

A 3D structure of positive ions and delocalised electrons held together by metallic bonds with strong electrostatic forces of attraction

60
Q

Greenhouse Effect

A

The process by which the absorption and subsequent emission of infrared radiation by atmospheric gases warms the lower atmosphere and the planet’s surface

61
Q

Group

A

A vertical column in the Periodic Table. Elements in a group have similar chemical properties and their atoms have the same number of outer shell electrons

62
Q

Hess’ Law

A

If a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route

63
Q

Heterogeneous catalysis

A

A reaction in which the catalyst has a different physical state from the reactants; frequently, reactants are gases which the catalyst is a solid

64
Q

Heterolytic fission

A

The breaking of a covalent bond with both of the bonded electrons going to one of the atoms forming a cation (+ ion) and an anion (- ion)

65
Q

Homogenous catalysis

A

A reaction in which the catalyst and reactants are in the same physical state, which is most frequently the aqueous or gaseous state

66
Q

Homologous series

A

A series of organic compound with the same functional group, but with each sucessive member differing by CH2

67
Q

Homolytic fission

A

The breaking of a covalent bond with one of the bonded electrons going to each atom, forming two radicals.

69
Q

Hydrated

A

Crystalline and containing water molecules

70
Q

Hydrocarbon

A

A compound of hydrogen and carbon only

71
Q

Hydrogen bond

A

A strong dipole-dipole attraction between an electron deficient hydrogen atom (Hδ+) and a lone pair of electrons on the highly electronegative atom on a different molecule (:Oδ-)

73
Q

Hydrolysis

A

A reaction with water or aqueous hydroxide ions that breaks a chemical compound into two chemical compounds

74
Q

Initiation

A

The first step in a radical substitution in which the radicals are generated by ultraviolet radiation

75
Q

Intermolecular forces

A

An attractive force between neighbouring molecules. They can be van der Waals forces (induced dipole-dipole forces), permanent dipole-dipole forces or hydrogen bonds

77
Q

Ion

A

A positively or negatively charged atom or (covalently bonded) group of atoms (molecular ion)

78
Q

Ionic bonding

A

The electrostatic attraction between oppositely charged ions

78
Q

Isotopes

A

Atoms of the same element with different numbers of neutrons and hence different masses

79
Q

le Chatlier’s principle

A

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

81
Q

Limiting Reagent

A

The substance in a chemical reaction that runs out first

81
Q

Lone pair

A

An outer shell pair of electrons not involved in bonding

82
Q

Mass (Nucleon) Number

A

The number of particles (protons and neutrons) in the nucleus

83
Q

Mechanism

A

A sequence of steps showing the path taken by electrons in a reaction

84
Q

Metallic bond

A

The electrostatic attraction between positive metal ions and delocalised electrons

85
Q

Molar Mass M

A

The mass per mole of a substance. The units of molar mass are g/mol

86
Q

Molar Volume

A

The volume per mole of gas. The units are dm^3/mol. At STP it is roughly 24dm^3/mol

88
Q

Mole

A

The amount of substance containing as many particles as there are atoms in 12g of the carbon-12 isotope

88
Q

Molecular Formula

A

The number of atoms of each element in a molecule

90
Q

Molecular Ion M+

A

The positive ion formed in mass spectronomy when a molecule loses an electron

91
Q

Molecule

A

A small group of atoms held together by covalent bonds

93
Q

Monomer

A

A small molecule that combines with many other monomers to form a polymer.

94
Q

Nomenclature

A

A method for naming compunds

95
Q

Nucleophile

A

An atom (or group of atoms) that is attracted to an electron-deficient centre or atoms where it donates a pair of electrons to forma new covalent bond

97
Q

Nucleophilic Substitiution

A

A type of substitution reaction in which a nucleophile is attracted to an electron-deficient centre or atom where it donates a pair of electrons to form a new covalent bond

97
Q

Oxidation

A

Loss of electrons or an increase in oxidation number

98
Q

Oxidation number

A

A measure of the number of electrons that an atom uses to bond with atoms of another element. Oxidation numbers are derived from a set of rules

99
Q

Oxidation Number Rules

A
100
Q

Oxidising agent

A

A reagent that oxidises (takes electrons from) another species

102
Q

Period

A

A horizontal row of elements in the Periodic table. Elements show trends across a period

102
Q

Percentage Yield Formula

A
104
Q

Periodicity

A

A regular periodic variation of properties of elements with atomic number and position in the periodic table

105
Q

Permanent Dipole

A

A small charge difference across a bond resulting from a difference in electronegativities of bonded atoms

105
Q

Permanent Dipole-Dipole Force

A

An attractive force between permanent dipoles in neighbouring molecules

107
Q

Pi-bond (π-bond)

A

The reactive part of a double bond formed above and below the plane of the bonded atoms by sideways overlap of p-orbitals

108
Q

Polar covalent bond

A

A bond with a permanent dipole

110
Q

Polar molecule

A

A molecule with an overall dipole, taking into account any dipoles across bonds. Generally non-symmetrical so dipoles do not cancel out.

111
Q

Polymer

A

A long molecular chain built up from monomer units

112
Q

Precipitation Reaction

A

The formation of a solid from a solution during a chemical reaction. Precipitates are often formed when two aqueous solutions are mixed together

112
Q

Principle Quantum number

A

A number representing the relative overall energy of each orbital, which increases with distance from the nucleus. The sets of orbitals with the same n value are referred to as electron shells or energy levels

113
Q

Propagation

A

Second stage in radical solution. Two repeated steps in radical solution that build up the products in a chain reaction. # (means a radical dot) Eg. XH3 react with #Cl, forming #XH2 and HCl then reacting #XH2 with Cl2 to form XH2Cl and #Cl

115
Q

Radical

A

A species with an unpaired electron

116
Q

Rate of reaction

A

The change in concentration of a reactant or product in a given time

117
Q

Redox reaction

A

A reaction in which both reduction and oxidation take place

118
Q

Reducing Agent

A

A reagent that reduces (adds electrons to) another species

119
Q

Reduction

A

Gain of electrons or a decrease in oxidation number

120
Q

Reflux

A

The continuous boiling and condensing of a reaction mixture to ensure that the reaction takes place without the contents of the flask boiling dry

122
Q

Relative Atomic Mass Ar

A

The weighted mean mass of an atom of an element compared to one twelfth of the mass of an atom of the carbon-12 isotope

123
Q

Relative Formula Mass

A

The weighted mean mass of a formula unit, compared to one twelfth of the mass of an atom of the carbon-12 isotope

123
Q

Relative Isotopic Mass

A

The mass of an atom of an isotope compared to one twelfth of the mass of an atom of the carbon-12 isotope

124
Q

Relative Molecular Mass Mr

A

The weighted mean mass of a molecule compared to one twelfth of the mass of an atom of the carbon-12 isotope

126
Q

Repeat Unit

A

A specific arrangement of atoms that occurs in the structure over and over again. Repeat units are included in brackets, outside of which the symbol is n

127
Q

Salt

A

A chemical compound formed by an acid when a H+ ion from the acid has been replaced by a metal ion or another positive ion, such as the ammonium ion NH4+

128
Q

Saturated Hydrocarbon

A

A hydrocarbon with single bonds only

129
Q

Shell

A

A group of atomic orbitals with the same principle quantum number, n. Also known as the main energy level

130
Q

Simple molecular lattice

A

A 3D structure of molecules bonded by weak intermolecular forces

131
Q

Skeletal Formula

A

A simplified organic formula, with hydrogen atoms removed from alkyl chains, leaving just a carbon skeleton and associated functional groups.

133
Q

Specific Heat Capacity, c

A

The energy required to raise the temperature of 1g of substance by 1°C. q=mcΔT

133
Q

Spectator Ions

A

Ions that are present but take no part in a chemical reaction

135
Q

Standard Conditions

A

A pressure of 100kPa (1 atmosphere), a stated temperature usually 298K (25°C) and a concentration of 1mol/dm^3 (if aqueous solution)

136
Q

Standard Enthalpy Change of Combustion (∆Hcө)

A

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

137
Q

Standard Enthalpy Change of Formation Standard Enthalpy Change of Combustion (∆Hfө)

A

The enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions

138
Q

Standard Enthalpy Change of Reaction Standard Enthalpy Change of Combustion (∆Hrө)

A

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

139
Q

Standard Solution

A

A solution of a known concentration. Normally used in titrations to determine unknown information about another substance

140
Q

Standard State

A

The physical state of a substance under the standard condisitons of 100kPa and 298K (25°C)

141
Q

Stereoisomer

A

Compounds with the same structural formula but a different arrangements of atoms in space

142
Q

Stoichiometry

A

The molar relationship between the relative quantities of substances taking part in the reaction

143
Q

Stratosphere

A

The second layer of the Earth’s atmosphere containing the “ozone layer” about 10km to 50km above the Earth’s surface

144
Q

Structural Formula

A

A formula showing the minimal detail for the arrangement of atoms in a molecule

145
Q

Structural Isomer

A

Compounds with the same molecular formula but a different structural formula

146
Q

Sub-shell

A

A group of the same type of atomic orbitals (s,p,d or f) within a shell

147
Q

Substitution Reaction

A

A reaction in which an atom or group of atoms is replaced with an atom or group of atoms

148
Q

Sucessive Ionisation Energy

A

A measure of the energy required to remove each electron in turn eg. the third ionisation energy is the energy required to go from 2+ to 3+

149
Q

Termination

A

The end step of radical substitution when two radicals combine to form a non-radical molecule

150
Q

Thermal decomposition

A

The breaking up of a chemical substance with heat into at least two chemical substances

151
Q

Troposphere

A

The lowest layer of the Earth’s atmosphere, extending from the Earth’s surface up to about 7km (above the poles) and to about 20km (above the tropics)

152
Q

Unsaturated hydrocarbons

A

A hydrocarbon containing carbon-carbon multiple bonds (normally double)

153
Q

van der Waals Forces

A

Very weak attractive forces between induced dipoles in neighbouring molecules

154
Q

Volatility

A

The ease that a liquid turns into a gas. Volatility increases as boiling point decreases

155
Q

Water of crystallisation

A

Water molecules that form an essential part of the crystalline structure of a compound

AS OCR Chemistry Definitions (2 decks)

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