Definitions

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  • Created by: JoP444
  • Created on: 15-03-14 14:12
Activation energy
The minimum energy required to start a reaction by the breaking of bonds.
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Anhydrous
A substance that contains no water molecules.
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Boltzmann distribution
A diagram showing the distribution of energies of the molecules at a particular temperature
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Bond dissociation enthalpy
The enthalpy change that takes place when breaking by homolytic fission 1 mol of a given bond in the molecules of a gaseous species
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Buffer solution
A system that minimises pH changes on addition of small amounts of an acid or a base
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Catalyst
A substance that increases the rate of a chemical reaction without being used up in the process
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cation
.An ionic species having a positive charge
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Concentration
The amount of solute, in mol, per 1 dm3 (1000 cm3) of solution.
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Covalen Bond
A bond formed by a shared pair of electrons.
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Cracking
The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-chained alkanes and alkenes
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Dative covalent
A shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only; also called a coordinate bond
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Dehydration
An elimination reaction in which water is removed from a saturated molecule to make an unsaturated molecule.
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Degradable polymer
Apolymer that breaks down into maller fragments when exposed tolight, heat or moisture
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Delocalised Electrons
electrons that are shared between more then two atoms
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Dipole–dipole force
An attractive force between permanent dipoles in neighbouring polar molecules
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Displacement reaction
A reaction in which a more reactive element displaces a less reactive element from an aqueous solution of its ions
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Disproportionation
The oxidation and reduction of the same species in a redox reaction
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Electron shielding
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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Electron(ic) structure or configuration
the arrangement of electrons in an atom
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Electronegativity
A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond
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Electrophile
An atom (or group of atoms) which 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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Empirical formula
The simplest whole-number ratio of atoms of each element present in a compound.
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Endothermic
A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken in from the surroundings (ΔH +ve).
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(Standard) enthalpy change of atomisation
The enthalpy change that takes place when one mole of gaseous atoms forms from the element in its standard state.
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(Standard) enthalpy change of combustion,
The enthalpy change that takes place 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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(Standard) enthalpy change of formation,
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
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(Standard) enthalpy change of reaction
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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Exothermic
A reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings (ΔH –ve).
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Functional group
The part of the organic molecule responsible for its chemical reactions
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General formula
The simplest algebraic formula of a member of a homologous series. For example, the general formula of the alkanes is CnH2n+2
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Giant covalent lattice
A three-dimensional structure of atoms, bonded together by strong covalent bonds.
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Giant ionic lattice
A three-dimensional structure of oppositely charged ions, bonded together by strong ionic bonds
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Giant metallic lattice
A three-dimensional structure of positive ions and delocalised electrons, bonded together by strong metallic bonds
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Group
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
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Half-life
The time taken for the concentration of a reactant to reduce by half.
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Hess’s Law
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
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Heterolytic fission
The breaking of a covalent bond with both of the bonded electrons going to each atom, forming a cation (+ ion) and an anion (– ion).
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Homolytic fission
The breaking of a covalent bond with one of the bonded electrons going to each atom, forming two radicals
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Hydrated
A crystalline compound containing water molecules
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Hydrogen bond
A strong dipole–dipole attraction between an electron-deficient hydrogen atom (O–Hδ+, N–Hδ+ or F–Hδ+) on one molecule and a lone pair of electrons on a highly electronegative atom (HδO:δ–, HδN:δ– HδF:δ–) on a different molecule.
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Intermolecular force
An attractive force between neighbouring molecules. Intermolecular forces can be van der Waals’ forces, dipole–dipole forces or hydrogen bonding
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Ion
A positively or negatively charged atom or a (covalently bonded) group of atoms (a molecular ion).
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Ionic bonding
The electrostatic attraction between oppositely charged ions.
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(First) ionisation energy
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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(Second) ionisation energy
The energy required to remove one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions.
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Isotopes
Atoms of the same element with different numbers of neutrons and different masses.
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Lattice enthalpy
The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions.
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Le Chatelier’s Principle
When a system in dynamic equilibrium is subjected to a change, the system readjusts itself to minimise the effect of the change and to restore equilibrium
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Lone Pair
An outer-shell pair of electrons that is not involved in chemical bonding.
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Metallic bond
The electrostatic attraction between positive metal ions and delocalised electrons
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Molar mass, M
The mass per mole of a substance. The units of molar mass are g mol–1
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Mole
The amount of any substance containing as many elementary particles as there are carbon atoms in exactly 12 g of the carbon-12 isotope.
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Molecular Fromula
The actual number of atoms of each element in a molecule
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Molecule
A small group of atoms held together by covalent bonds.
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Monomer
A small molecule that combines with many other monomers to form a polymer.
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Neutralisation
A chemical reaction in which an acid and a base react together to produce a salt and water.
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Nucleophile
An atom (or group of atoms) which is attracted to an electron- deficient centre or atom, where it donates a pair of electrons to form a new covalent bond.
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Oxidation
Loss of electrons or an increase in oxidation number.
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Oxidising agent
A reagent that oxidises (takes electrons from) another species.
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Percentage yield
(Actual amount of product / Theoretical amount of product) *100
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Period
A horizontal row of elements in the Periodic Table. Elements show trends in properties across a period.
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Periodicity
A regular periodic variation of properties of elements with atomic number and position in the Periodic Table.
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Permanent dipole
A small charge difference across a bond resulting from a difference in electronegativities of the bonded atoms.
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Polar molecule
A molecule with an overall dipole, having taken into account any dipoles across bonds
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Propagation
The two repeated steps in radical substitution which build up the products in a chain reaction.
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Radical
A species with an unpaired electron
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Rate of Reaction
The change in concentration of a reactant or a product in a given time.
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Reduction
Gain of electrons or a decrease in oxidation number
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Reducing agent
A reagent that reduces (adds electrons to) another species
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Reflux
The continuous boiling and condensing of a reaction mixture to ensure that the reaction takes place without the contents of the flask boiling dry
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Relative atomic mass, Ar
The weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12
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Relative isotopic mass
The mass of an atom of an isotope compared with one-twelfth of the mass of an atom of carbon-12.
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Relative molecular mass, Mr
The weighted mean mass of a molecule of a compound compared with one-twelfth of the mass of an atom of carbon-12.
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Salt
A chemical compound formed from an acid, when an H+ ion from the acid has been replaced by a metal ion or another positive ion, such as the ammonium ion, NH4+.
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Shell
A group of atomic orbitals with the same principal quantum number, n. Also known as a main energy level.
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Specific heat capacity, c
The energy required to raise the temperature of 1 g of a substance by 1 °C.
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Spectator ions
Ions that are present but play no part in a chemical reaction
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Standard Conditions
A pressure of 100 kPa (1 atmosphere), a stated temperature, usually 298 K (25 °C) and a concentration of 1 mol dm–3 (for reactions with aqueous solutions).
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Stereoisomers
Compounds with the same structural formula but with a different arrangement of the atoms in space.
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Structural isomers
Molecules with the same molecular formula but with different structural arrangements of atoms.
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Sub-shell
A group of the same type of atomic orbitals (s, p, d or f) within a shell.
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Substitution reaction
A reaction in which an atom or group of atoms is replaced with a different atom or group of atoms.
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Termination
The step at the end of a radical substitution when two radicals combine to form a molecule.
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Thermal decomposition
The breaking up of a chemical substance with heat into at least two chemical substances.
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Valence Shell
The outermost shell of an atom, which contains the electrons most likely to react and bond to other atoms.
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van der Waals’ force
An attractive force between instantaneous dipoles and induced dipoles in neighbouring molecules
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Volatility
The ease with which a liquid turns into a gas. Volatility increases as boiling point decreases.
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Anion
An ionic species having a negative charge
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Other cards in this set

Card 2

Front

A substance that contains no water molecules.

Back

Anhydrous

Card 3

Front

A diagram showing the distribution of energies of the molecules at a particular temperature

Back

Preview of the back of card 3

Card 4

Front

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

Back

Preview of the back of card 4

Card 5

Front

A system that minimises pH changes on addition of small amounts of an acid or a base

Back

Preview of the back of card 5
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