OCR-A A-level Chemistry

Definitions & Key Facts

relative isotopic mass

mass of an atom of an isotope compared to 1/12 the mass of an
atom of carbon-12

relative atomic mass

average mass of the atoms of an
element
taking account of all of the isotopes
compared to 1/12 the mass of an
atom of carbon-12

relative molecular mass

average mass of a molecule
compared to 1/12 the mass of an
atom of carbon-12

isotopes

atoms of the same element with
the same number of protons
but different numbers of neutrons

spectator ions

species which are not changing physical state or oxidation state... not in an ionic equation

mole

amount of substance in grams which contains the same number of particles as there are atoms in 12g of carbon-12

empirical formula

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

general formula

algebraic formula
for a homologous series

molecular formula

actual number of atoms of each element in a molecule

structural formula

minimum detail required to understand the structure of a molecule

displayed formula

shows all the covalent bonds in a molecule

skeletal formula

shown by removing hydrogen atoms from alkyl chains, leaving just a carbon skeleton and associated functional groups

% yield

(actual yield/theoretical yield) x 100

% atom economy

mass of desired product / total mass of reactants x 100

Bronsted-Lowry acid

proton donor

Bronsted-Lowry base

proton acceptor

alkali

soluble base which releases OH⁻ ions in solution

salt

ionic compound that forms when H⁺ ion in an acid is replaced by a metal ion or the ammonium ion

strong acid

acid which
completely dissociates
in aqueous solution

weak acid

acid which partially dissociates
in aqueous solution

% uncertainty

(uncertainty/measurement) x 100 x number of measurements

oxidation

addition of oxygen
loss of hydrogen
loss of electrons
increase in oxidation state

reduction

loss of oxygen
gain of hydrogen
gain of electrons
decrease in oxidation state

disproportionation

simultaneous
oxidation and reduction
of the same element

oxidising agent

electron acceptor

reducing agent

electron donor

orbital

region of space which can be
occupied by a maximum of 2
electrons
with opposite spin

ionic bond

electrostatic attraction between positive metal ions and negative non-metal ions

metallic bond

electrostatic attraction between positive metal ions
and delocalised electrons.

covalent bond

electrostatic attraction between
a pair of bonded nuclei
and a bonding pair of electrons

dative bond

electrostatic attraction between
a pair of bonded nuclei
and a bonding pair of electrons
which originate from one of the
bonded atoms

BeCl₂

Be is in Grp2
2 outer electrons
2 bp
repel equally
get as far apart as possible

linear
180°

BF₃

B is in Grp3
3 outer electrons
3 bp
repel equally
get as far apart as possible

trigonal planar
120°

CH₄

C is in Grp4
4 outer electrons
4 bp
repel equally
get as far apart as possible

tetrahedral
109.5°

NH₃

N is in Grp5
5 outer electrons
3 bp and 1 lp
lp : bp repulsion ＞ bp : bp repulsion
get as far apart as possible

trigonal pyramid
107°

H₂O

O is in Grp6
6 outer electrons
2 bp and 2 lp
lp : lp repulsion ＞ lp : bp repulsion ＞ bp : bp repulsion
get as far apart as possible

V-shape / Bent / Non-linear
104.5°

SF₆

S is in Grp6
6 outer electrons
6 bp
repel equally
get as far apart as possible

Octahedral
90° and 180°

electronegativity

ability of an atom to attract
electrons within a covalent bond

London forces

induced dipole-dipole forces
instantaneous dipole-induced dipole forces
dispersion forces

random movement of the electron cloud
causes an uneven charge
distribution
and sets up an instantaneous
dipole in one molecule

this induces a dipole in a
neighbouring molecule
and leads to a temporary
attraction

permanent dipole-permanent dipole force

intermolecular force between permanent dipoles in
neighbouring polar molecules

hydrogen bond

strong intermolecular force between a δ⁺H atom covalently bonded to
N, O or F on one molecule

and a lone pair of electrons on
N, O or F of a neighbouring
molecule

periodicity

repeating pattern of chemical and physical properties across different periods

first ionisation energy

energy required to remove
1 mole of electrons from
1 mole of gaseous atoms to form
1 mole of +1 gaseous ions

second ionisation energy

energy required to remove
1 mole of electrons from
1 mole of +1 gaseous ions to form
1 mole of +2 gaseous ions

exothermic

bond making process

endothermic

bond breaking process

activation energy

minimum amount of energy
required to start a chemical reaction

standard conditions (⦵)

298 K
100 kPa
all solutions 1 moldm⁻³

standard enthalpy change of formation △fH⦵

enthalpy change when...

1 mole of a compound is formed
from its elements in their
standard states

under standard conditions of
298K and 100kPa

with all reactants and products in
their standard states

standard enthalpy change of combustion △cH⦵

enthalpy change when...

1 mole of a substance
completely combusts in excess
oxygen

under standard conditions of
298K and 100kPa

with all reactants and products in
their standard states

standard enthalpy change of reaction △rH⦵

enthalpy change when...

the reaction occurs in the molar ratio specified by the balanced equation

under standard conditions of
298K and 100kPa

with all reactants and products in
their standard states

standard enthalpy change of neutralisation △neutH⦵

enthalpy change when...

1 mole of water is formed from a
reaction between an acid & a base

under standard conditions of
298K and 100kPa

Q

Q \= mc△T

△H

△H \= ⁻Q/1000n

mean bond enthalpy

energy required to break 1 mole
of gaseous covalent bonds

averaged over a number of
different molecules

Hess' law

enthalpy change of a reaction is
independent of the route taken

providing the initial and final
conditions are the same

catalyst

speeds up a reaction

regenerated
doesn't appear in the overall
equation
provides an alternative reaction
pathway
with a lower activation energy

heterogenious catalyst

catalyst in a different physical state to the reactants

homogenious catalyst

catalyst in the same physical state as the reactants

dynamic equilibrium

forward rate \= back rate
concentrations of all reactants
and products are constant
closed system

Le Chatelier's principle

when the conditions of a system
in equilibrium are changed

the position of equilibrium will
shift to reduce the effect of the
change

saturated

single carbon-carbon bonds only

unsaturated

compound with one or more double or triple carbon-carbon bonds

aliphatic

compound containing carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings

alicyclic

aliphatic compound arranged in non-aromatic rings with or without side chains

aromatic

compound containing at least one benzene ring

homologous series

series of organic compounds
with the..
same functional group
same general formula
successive member differs
by CH₂

functional group

atom, group of atoms or region of a molecule responsible for its reactions and properties

structural isomers

same molecular formula
different structural formula

stereoisomers

same molecular formula
same structural formula
different arrangement of atoms
in space

radical

species with an unpaired electron

homolytic fission

covalent bond breaking process where each atom receives one of the bonding electrons

forms radicals

heterolytic fission

covalent bond breaking process where one atom receives both of the bonding electrons

forms ions

sigma bond

covalent bond formed by end-on overlap of orbitals

pi bond

covalent bond formed by sideways overlap of p-orbitals

3 types of stereoisomers

E-Z isomers

cis-trans isomers

optical isomers

E-Z isomerism

type of stereoisomerism

restricted rotation about a C\=C double bond

each C in the C\=C double bond attached to 2 different atoms or groups

cis-trans isomerism

type of stereoisomerism

restricted rotation about a C\=C double bond

a particular atom or group is attached to each of the C atoms in the C\=C double bond

like groups on opposite sides of the double bond - trans
like groups on same side of the double bond - cis

also found in square planar and octahedral complexes

optical isomerism

type of stereoisomerism

occurs when there is an asymmetric (chiral) carbon atom attached to 4 different atoms or groups resulting in non-superimposable mirror images (enantiomers)

occurs where there are two or three bidentate ligands in an octahedral complex

nucleophile

electron pair donor

electrophile

electron pair acceptor

carbocation

positively charged organic species

1° carbocation

positive C
is bonded to 1 other C

2° carbocation

positive C
is bonded to 2 other Cs

3° carbocation

positive C
is bonded to 3 other Cs

Markownikoff's rule

rule applied to determine the product mixture when...

an asymmetric alkene reacts with
an asymmetric electrophile

major product is formed from the more stable 2° or 3° carbocation

primary alcohol

C to which the OH is bonded,
is bonded to 1 other C

secondary alcohol

C to which the OH is bonded,
is bonded to 2 other Cs

tertiary alcohol

C to which the OH is bonded,
is bonded to 3 other Cs

hydrocarbon

compound that contains
carbon and hydrogen only

CFC

compound that contains chlorine, fluorine and carbon only

HFC

compound that contains hydrogen, fluorine and carbon only

fingerprint region

complicated region of an IR spectrum below 1500 cm⁻¹
caused by vibrations of the whole molecule
compared to a spectral database for a positive ID

molecular ion

molecule minus an electron

fragmentation

process where a molecular ion breaks into a positive ion and a radical

Alkane to Haloalkane

Halogen UV light

Rad Sub

Alkene to Alkane

H2, Ni catalyst

Reduction

Heterogenious Catalysis

Alkene to Polyalkene

High pressure and a catalyst

Addition Polymerisation

Alkene to Dihaloalkane

X2 rtp

Elec Add

Alkene to Haloalkane

HX rtp

Elec Add