Key Definitions Y1 Chem

Acid

a species that releases H+ ions in aqueous solution

Activation energy

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

Actual yield

the amount of product obtained from a reaction

Addition polymerisation

formation of a very long molecular chain (addition polymer), by repeated addition reactions of many unsaturated alkene molecules (monomers)

Addition reaction

a reaction in which two reactants join together to form one product

Adsorption

the process that occurs when a gas or liquid or solute is held to the surface of a solid

Alicyclic

containing carbon atoms joined together in a ring that is not aromatic

Aliphatic

containing carbon atoms joined together in unbranched (straight) or branched chains

Alkali

a type of base that dissolves in water to release hydroxide ions, OH-

Alkanes

the hydrocarbon homologous series with the general formula CnH2n+2

Alkenes

the hydrocarbon homologous series with at least one double carbon bond

Alkyl group

a side chain formed by removing a hydrogen atom removed from an alkane parent chain (often shown as ‘R’)

Alkynes

the hydrocarbon homologous series with at least one triple carbon bond

Amount of substance

the quantity whose unit of the mole. Chemists use amount of substance as a means of counting atoms

Anhydrous

containing no water molecules

Anion

a negatively charged ion with more electrons than protons

Aromatic

containing one or more benzene rings

Atom economy

(sum of molar masses of desired products / sum of molar masses of all products) X100

Atomic

the number of protons in the nucleus of an atom (also proton number)

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 one mole of a given type of bond in the molecules of a gaseous species

Avogadro constant

the number of atoms per mole of carbon 12

Avogadro's hypothesis

equal volumes of gases at the same temperature and pressure contain the same number of molecules

Base

a compound that neutralises an acid to form a salt

Binary compound

a compound containing two elements only

Bond angle

the angle between two bonds at an atom

Bonded pair

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

Catalyst

a substance that increases the rate of a chemical reaction without being used up in the process, a catalyst provides an alternative route for the reaction with lower activation energy

Cation

a positively charged ion with fewer electrons than protons

Chain reaction

a reaction in which the propagation steps release new radicals that continue the reaction

Cis-trans isomerism

a special type of E/Z isomerism in which there are 2 non hydrogen groups and 2 hydrogen atoms around the carbon double bond - the cis isomer (z) has hydrogen atoms on each carbon on the same side whilst the trans isomer (e) has hydrogen 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

Dative covalent bond

a shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only

Covalent bonding

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

Dehydration

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

Delocalised electrons

shared between more than 2 atoms

Desorption

release of an adsorbed substance from a surface

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 a small negative charge

Dipole-dipole force

an attractive force between permanent dipoles in neighbouring polar molecules

Displacement reaction

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

Displayed formula

a formula that shows the relative positioning of all the atoms in a molecule and the bonds between them

Disproportionation

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

Dynamic equilibrium

the equilibrium 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 carbon of a double bond may be arranged differently in space because of the restricted rotation of the double bond

Electronegativity

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

Electrophile

an atom or group of atoms that is attracted to an electron rich centre, where it accepts a pair of electrons (lone pair acceptor)

Electrophilic addition

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

Elimination reaction

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

Empirical formula

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

End point

the point in a titration where the indicator changes colour; the end point indicates whether the reaction is just complete

Endothermic reaction

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

Enthalpy

the heat content that is stored in chemical system

Enthalpy change

difference in enthalpy between reactants and products in a reaction

Equilibrium constant

a measure of the position of equilibrium; the magnitude of an equilibrium constant indicates whether there are more reactants or more products in an equilibrium system

Exothermic reaction

a reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings

Fingerprint region

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

First ionisation energy

the energy required 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 their differences in 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 to 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

Giant covalent lattice

3D structure of atoms, bonded together by strong covalent bonds

Giant ionic lattice

3D structure of oppositely charged ions, bonded together by strong ionic bonds

Giant metallic lattice

3D structure of positive ions and delocalised electrons, bonded together by strong metallic bonds

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

Hess’ 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 has a different physical state from the reactants; frequently reactants are gases whilst the catalyst is a solid

Heterolytic fission

the breaking of a covalent bond forming a cation and an anion

Homogeneous catalysis

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

Homologous series

a series of organic compounds with the same functional group but with each successive member differing by CH2

Homolytic fission

the breaking of a covalent bond with one of the bonded electrons going to each atom, forming 2 radicals

Hydrated

a crystalline compound containing water molecules

Hydrocarbon

compound containing carbon and hydrogen only

Hydrogen bond

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

Hydrolysis

a reaction with water that breaks a chemical compound into 2 compounds, the H and OH in a water molecule becomes incorporated into the 2 compounds

Induced dipole-dipole reaction

attractive forces between induced dipoles in different molecules, also called london forces

Initiation

the first stage in a radical reaction in which radicals starts when a covalent bond is broken by homolytic fission

Intermediate

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

Intermolecular forces

an attractive force between molecules. Intermolecular forces can be london forces, permanent dipole-dipole interactions or hydrogen bonding

Ion

a positively or negatively charged atom or a (covalently bonded) group of atoms (polyatomic ion), where the number of electrons is different from the number of protons

Ionic bonding

the electrostatic attraction between positive and negative ions

Isotope

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

Le Chatelier’s principle

when a system in dynamic equilibrium is subjected to an external change, the system readjusts itself to minimise the effect of the change and to restore equilibrium

Limiting reagent

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

London forces

attractive forces between induced dipoles in different molecules also known as induced dipole-dipole interactions

Lone pair

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

Mass number A

the sum of the number of protons and neutrons in the nucleus; also known as nucleon number

Metallic bonding

the electrostatic attraction between positive metal ions and delocalised electrons

Concentration

the amount of solute, in moles, dissolved in 1dm^3 of solution

Molar gas volume Vm

the volume per mole of gas molecules at a stated temperature and pressure

Molar mass

the mass per mole of a substance in units of gmol ^-1

Mole

the amount of any substance containing as many elementary particles as there are carbon atoms in exactly 12g of the carbon-12 isotope i.e 6.02 x 10^23

Molecular formula

a 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 a covalent compound that can exist while retaining its chemical identity, consisting of 2 or more atoms covalently bonded together

Monomer

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

Neutralisation

the reaction between an acid and a base to produce a salt

Non-polar

with no charge separation across a bond or in a molecule

Nucleophile

an atom or group of atoms that is attracted to an electron deficient carbon atom, where it donates a pair of electrons to form a new covalent bond