Year 1 /AS OCR A LEVEL Chemistry Definitions

Acid

A species that releases H+ ions in aqueous solution

Activation Energy

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

Actual Yield

The amount of product obtained from a reaction

Addition Polymerisation

Formation of a very long molecular chain by repeated addition of many unsaturated alkene molecules (monomers)

Addition Reaction

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

Alicyclic

Containing carbon atoms joined together in a ring that isn't aromatic

Alkali

A type of base that dissolves in water forming hydroxide ions

Alkanes

The hydrocarbon homologous series with single carbon bonds CnH2n+2

Alkenes

The hydrocarbon homologous series with at least one double carbon bond CnH2n

Alkyl Group

A side chain formed by removing a hydrogen from the alkane parent chain eg CH3

Amount of Substance

The quantity measured in moles used to count atoms, ions and molecules

Anhydrous

Containing no water molecules

Anion

A negatively charged ion

Aromatic

Containing one or more benzine ring

Atom Economy

(Sum of molar masses of desired products) / (Sum of molar masses of all products) x 100

Atomic (proton) Number

Number of protons in the nucleus of an atom

Atomic Orbital

A region around the nucleus that can hold up to two electrons with opposite spins

Average Bond Enthalpy

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

Avogadro Constant

The number of atoms per mole of the carbon-12 isotope (6.02 x 10^23)

Base

A compound that neutralises an acid to form a salt

Bond Angle

The angle between two bonds at an atom

Bonded Pair

A pair of electrons shared between two electrons to make a covalent bond

Carbocation

An ion that contains a positively charged carbon atom

Catalyst

A substance that increases the rate of a reaction without being used up. Provides an alternative route with lower activation energy.

Cation

A positively charged ion

Chain Reaction

A reaction in which the propagation steps release new radicals which continue the reaction

Cis/Trans Isomerism

A special type of EZ isomerism in which there are two non-hydrogen groups and two hydrogen atoms around the C=C double bond, the cis isomer has H atoms on each carbon on the same side. The trans-isomer has H atoms on each carbon on different sides

Closed system

A system isolated from its surroundings

Collision theory

Two reacting particles must collide for a reaction to occur and must be in the correct orientation and have sufficient energy to overcome the activation energy of the reaction

Concentration

The amount of solute in moles dissolved in 1 dm cubed of solution

Condensation reaction

Reaction in which two small molecules react together to form a larger molecule with elimination of a small water molecule

Covalent bond

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

Dative covalent

Shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only, also called a coordiate bond

Dehydration

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

Delocalised electrons

Electrons shared between two or more atoms

Dipole

A separation in electrical charge so that one atom of a polar covalent bond, or one end of a polar molecule has a small positive charge and the other has a small negative charge

Displacement reaction

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

Displayed formula

Formula showing the relative positioning of all the atoms in a molecule and the bond between them

Disproportionation

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

Dynamic equilibrium

The equilibriums that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction and concentrations do not change

E/Z isomerism

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

Electron configuration

Shorthand representation that shows electrons occupy subshells in an atom

Electronegativity

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

Electrophile

And atom (or group of atoms) which is attracted to an electron rich centre or atom, where accept a pair of electrons to form a new covalent bond

Electrophilic addition

And addition reaction in which the first step is an attack by an electrophile on a region of high electron density

Electrophilic substitution

Type of substitution reaction in which an electrophile is attracted to an electron rich centre or atom where it excepts a pair of electrons to form a new covalent bond

Empirical formula

Formula that shows the simplest whole number ratio of atoms of each element present in a compound

Endpoint

The point in a titration where the indicator changes colour, the endpoint indicates when the reaction is just complete

Endothermic reaction

Reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in the heat being taken from the surroundings (Delta H is positive)

Enthalpy change

The difference between the enthalpy of the products and the enthalpy of the reactants

Enthalpy cycle

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

Enthalpy profile diagram

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

Equilibrium constant Kc

A measure of the position of equilibrium, the magnitude of an equilibriums constant indicates whether there are more reactants or more products in an equilibriums system

Exothermic reaction

A reaction in which the enthalpy of the product is smaller than the enthalpy of the reactants resulting in heat lost to the surroundings (Delta H is negative)

Fingerprint region

Area of an infrared spectrum below 1500 cm^-1 that gives a characteristic pattern for different compounds

First ionisation energy

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

Fractional distillation

The separation of components in a liquid mixture by the different boiling points into fractions with different compositions

Fragment ions

Ions formed from the breakdown of the molecular ion in a mass spectrometer

Fragmentation

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

Functional group

The part of the organic molecule responsible for its chemical reactions

General formula

The simplest algebraic formula of a member of a homologous series

Giant covalent lattice

A three-dimensional structure of atoms bonded together by strong covalent bonds

Giant ionic lattice

A three-dimensional structure of oppositely charged ions, bonded together by strong ionic bonds

Giant metallic lattice

A three-dimensional structure of positive irons and delocalised electrons, bonded together by strong metallic bonds

Group

Vertical column in the periodic table. Elements in a group of similar chemical properties and their atoms of the same number of outer electron shells

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

Heterogeneous catalysis

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

Heterolytic fission

The breaking of a covalent bond with both the bonded electrons going to one atom forming a cation and an anion

Homogeneous catalysis

Reaction in which the catalyst in the reactants are in the same physical state

Homologous series

A series of organic compounds with the same functional group but with each successive member differing by CH3

Homolytic fission

Breaking of a covalent bond with one of the bond of electrons going to each atom forming a radical

Hydrated

Crystalline compound containing water molecules

Hydrocarbon

A compound of hydrogen and carbon only

Hydrogen bond

The strong dipole dipole attraction between electron deficient hydrogen atom of -NH, -OH, -HF on one molecule and lone pair of electrons on a highly electronegative atom containing N, O or F on a different molecule

Hydrolysis

Reaction with water that breaks chemical compound in to two compounds, the H and OH in a water molecule becomes incorporated into the two compounds

Induced dipole dipole interaction

Attractive forces between induced dipole in different molecules, also called London forces

Infrared spectroscopy

And instrumentation method of analysis that identifies bonds from absorption of the infrared radiation on different wavelengths

Initiation

The first stage in a radical reaction in which radicals start when a covalent bond is broken by homolytic fission of a covalent bond

Intermediate

Species formed during a reaction that reacts further and is not present in the final products

Intermolecular force

Trying to force between molecules. Intermolecular forces can be London forces, permanent dipole dipole interactions or hydrogen bonding

Ion

Are positively or negatively charged atom or group of atoms, where the number of electrons is different from the number of protons

Ionic bonding

The electrostatic attraction between positive and negative ions

Isotopes

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

Le Chatelier's principal

When the system and dynamic equilibrium is subjected to an external change, the system readjusts its self to minimise the effect of the change and restore equilibrium

Limiting reagent

Reactant that is not in excess, will be used up first and stop the reaction

Lone pair

And outer shell pair of electrons of that is not involved in chemical bonding

Mass number

Sum of the number of protons and neutrons in the nucleus

Metallic bond

Electrostatic attraction between positive metal ions and delocalised electrons

Molar mass

Mass per mole of a substance, measured in gmol-1

Mole

Amount of any substance containing as many elementary particles as there are carbon atoms in exactly 12 g of carbon 12 isotope, that is 6.02 x 10^23 particles

Molecular formula

Formula that shows the number and type of atoms of each element present in a molecule

Molecular ion

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

Molecule

The smallest part of the covalent compound that can exist will retain its chemical identity, consisting of two or more atoms covalently bonded together

Monomer

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

Neutralisation

A chemical reaction in which an acid and a base react together to produce a salt

Nomenclature

A system of naming compounds

Non-polar

With no charge separation across a bond or in a molecule

Nucleophile

An atom (or group of atoms) which is attracted to an electron deficient centre or atom, where donates a pair of electrons to form a new covalent bond

Nucleophilic substitution

Reaction in which a nucleophile is attracted to an electron deficient carbon atom and replaces an atom or group of atoms on the carbon atom

Oxidation

Loss of electrons or an increase in oxidation number