Activated complex
Activation energy
Atomic number
Average rate of
reaction
Avogadro constant, L
Catalyst
Catalyst poisoning
Covalent radius
Delocalised electrons
Electron
An unstable
arrangement of
atoms formed at the
maximum of the
potential energy
barrier during a
chemical reaction; X.
The number of protons in the nucleus
of an atom.
The number of formula units in the
formula mass of a substance, e.g. the
number of molecules in 18g of water.
L = 6.02 x 1023 mol-1.
This occurs when a
substance forms strong
bonds with the surface
of a catalyst, blocking
the active site and
reducing its efficiency.
Electrons which are not confined to a
single orbital between a pair of atoms,
e.g. in metallic bonding. The benzene
ring also has delocalised electrons.
The energy required
by colliding molecules
to form an activated
complex.
The change in mass or concentration of
a reactant or product divided by the
time interval during which the change
occurs.
A substance which
speeds up a reaction
without being used up.
It lowers the activation
energy of the reaction.
A measure of atomic size, being half the
distance between the nuclei of
two covalently bonded atoms
of an element. Covalent bond
lengths between two atoms
can be obtained by adding the appropriate
covalent atomic radii.
A particle which moves around the
nucleus of an atom. It has a single
negative charge but its mass is
negligible compared to that of a
proton or neutron.
Electronegativity
Endothermic reaction
Enthalpy change
Enthalpy of combustion
Enthalpy of
neutralisation of an acid
Enthalpy of solution
Exothermic reaction
Group
Heterogeneous catalyst Homogeneous catalyst
The strength of the attraction by an atom of
an element for its bonding electrons. If the
electronegativities of two atoms sharing
electrons is similar, the bond will be almost
purely covalent. The greater the difference,
the more likely the bond is to be polar or
even ionic.
A reaction in which heat energy is absorbed
from the surroundings. It has a positive
enthalpy change, H +ve.
The enthalpy change
The difference in heat energy between when one mole of a
substance is
reactants and products in a chemical
completely burned
reaction.
in oxygen.
The enthalpy
change when the
acid is neutralised
to form one mole
of water. The
enthalpy of neutralisation of a base
can be similarly defined.
The enthalpy change
when one mole of a
substance is dissolved
in water.
A reaction in which heat energy is released
to the surroundings. It has a negative
enthalpy change, H –ve.
A column of elements in the Periodic
Table. The atomic size increases down
a group and the electronegativity
decreases.
The chemical properties of the
elements on the group are similar.
A catalyst which is in a different
physical state from the reactants.
A catalyst which is in the same physical
state to the reactants.
Hydrogen bonding
Intermolecular bonding
Intramolecular bonding
Ionic bond
Ionisation
Ionisation enthalpy
Isotopes
Lattice
Mass number
Metallic bonding
Intermolecular forces of attraction. The
molecules must contain
highly polar bonds in
which hydrogen atoms are
bonded to N, O or F. They
are a stronger type of
dipole-dipole interactions.
Forces between
molecules e.g. van der
Waals; dipole-dipole
interactions or hydrogen bonds.
They are much weaker than intramolecular
bonds.
Bonds between atoms of
molecules, i.e. covalent
and polar covalent bonds.
Bond formed as a result of attraction
between positive and negative ions.
The loss or gain of electrons by neutral
atoms to form ions.
Atoms of the same element which
have different numbers of neutrons.
They have the same atomic number
but different mass numbers.
The total number of protons and
neutrons in the nucleus of an atom.
Is the energy required to remove one mole
of electrons from one mole of gaseous
atoms, e.g. Na(g)  Na+(g) + e
The three-dimentional
arrangement of positive and
negative ions in the solid
state of ionic compounds.
The bonding responsible for metallic
properties. Each atom loses its outer
electrons to form positive ions. These
ions pack together in a regular
arrangement with the delocalised
electrons binding the ions together.
Molar volume
Molecule
Neutron
Nucleus
Period
Polar covalent bonds
Proton
Ion
Active site
Adsorption
The volume of a mole of gas at a
specified temperature and pressure.
(approximately 24L mol-1)
A group of atoms held together by
covalent bonds.
A particle found in the nucleus of an
atom. It has the same mass as a
proton but no charge.
The extremely small centre of an atom
where the neutrons and protons are
found.
A horizontal row in the Periodic Table.
Atomic size decreases across a period
and electronegativity increases.
A particle found in the nucleus of an
atom. It has a single positive charge
and the same mass of a neutron.
The active site in an enzyme contains
groups of atoms which can bind to
other molecules (substrates).
Bonds formed between non-metallic atoms by
sharing a pair of electrons. If the atoms have quite
different electronegativities the electrons are not
shared equally, the more electronegative atoms
become slightly negative in
comparision to the other
atom. As a result the bond is
‘polar’.
Atoms or groups of atoms which
possess an positive or negative charge
due to the loss or gain of electrons,
e.g. Na+ and CO32-.
Adsorption occurs
when molecules
become bonded to
the surface of a
catalyst, this
weaken the internal
bonds of the
molecule.
Formula unit
Fullerenes
Potential energy
diagram
Specific heat capacity
Substrate
Van der Waals’ forces
A formula unit may be an
atom (for all elements
which do not exist as
diatomic molecules), a
molecule (for all covalent
molecular substances) or
the simplest ratio of atoms
or ions (for network or
lattice substances).
This shows the enthalpy of reactants
and products, and the enthalpy change
during a chemical reaction.
The substrate is the reactant in a
reaction catalysed by an enzyme.
These are molecules of pure carbon
constructed from 5- and 6-membered
rings combined into hollow structures.
They have a discrete covalent
molecular structure. The most stable
contains 60 carbon atoms in a shape
resembling a football.
This relates the energy change in a
liquid to the change in temperature.
For water it has a value of 4.18 kJ kg-1
⁰C-1. In other words, when 1 kg of
water absorbs 4.18 kJ of heat its
temperature will rise by 1⁰C.
These are the intermolecular forces of attraction
which result from the electrostatic attraction
between temporary dipoles and induced dipoles;
they are caused by movement
of electrons in atoms and
molecules.
They increase in strength as the
dipole increases in mass.