Chemsitry Unit 1 and 2 definitions

Acid

A species that is a proton donor

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Activation energy

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

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Addition polymerisation

The process in which unsaturated alkene molecules (monomers) add on to a growing polymer chain one at a time to form a very long saturated molecular chain (the addition polymer)

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Addition reaction

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

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Adsorption

The process that occurs when a gas, liquid or solute is held to the surface of a solid (or ore rarely, a liquid)

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Alicyclic hydrocarbon

A hydrocarbon with carbon atoms joined together in a ring structure

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Aliphatic hydrocarbon

A hydrocarbon with carbon atoms joined together in straight or branched chains

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Alkali

A type of base that dissolves in water, forming hydroxide ion, OH-(aq)

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Alkane

A member of the homologous series with the general formula CnH2n+2

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Alkyl group

An alkane with a hydrogen atom removed, e.g. CH3, C2H5; alkyl groups are often shown as R

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Amount of substance

The quantity whose unit is the mole. Chemists use this as a means of counting atoms.

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Anhydrous

Containing no water molecules

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Anion

A negatively charged ion

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Atom economy

Molecular mass of desired product x 100 Sum of molecular masses of all products

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Atomic orbital

A region within an atom that can hold up to 2 electrons, with opposite spin

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Atomic (proton) number

The number of protons in the nucleus of an atom

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Average bond enthalpy

The average enthalpy change that takes place when breaking by homiletic fission 1 mole of a given type of bond in the molecules of a gaseous substance

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Avogadro constant NA

The number of atoms per mole of the C-12 isotope (6.02 x 10 23 mol -1)

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Base

A species that is a proton acceptor

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Biodegradable material

A substance that is broken down naturally in the environment by living organisms

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Boltzmann distribution

The distribution of energies of molecules at a particular temperature, usually shown as a graph

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Bond enthalpy

The enthalpy change that takes place when breaking by homolytic fission1 mole of a given bond in the molecules of a gaseous process

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Carbanion

An organic ion in which a carbon atom has a negative charge

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Carbocation

An organic ion in which a carbon atom has a positive charge

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Catalyst

A substance that increases the rate of a reaction without being used up itself in the process

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Cation

A positively charged ion

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Cis-trans isomerism

A special type of E/Z isomerism in which there is a non-hydrogen group and hydrogen on each C of a C=C double bond: the cis-isomer (Z) has H atoms on each carbon on same side; the trans-isomer (E) has H atoms on each carbon on different sides

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Compound

A substance formed from 2 or more chemically bonded elements in a fixed ratio, usually shown by a chemical formula

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Concentration

The amount of solute (mol) per 1 dm3 (1000cm3) of solution

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Covalent bond

A bond formed by a shared pair of electrons

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Cracking

The breaking down of along-chain saturated hydrocarbons to form a mixture of shorter-chained alkanes and alkenes

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Curly arrow

A symbol used in reaction mechanisms to show the movement of an electron pair in the breaking or formation of a covalent bond

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Dative covalent (or coordinate) bond

A covalent bond where the shared pair of electrons has only been supplied by one of the bonding atoms

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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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Delocalised electrons

Electrons that are shared between more than 2 atoms

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Displacement reaction

A reaction in which a more reactive element displaces a less reactive one from an aqueous solution of the latter's ions

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Displayed formula

A formula showing the relative positioning of all the atoms in a molecule and the bonds between them

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Disproportionation

The oxidation and reduction of the same element in a redox reaction

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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

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E/Z isomerism

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

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Electron 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 of a covalent bond

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Electron shielding

Repulsion between electrons in different ring shells. It reduces the net attractive force from the positive nucleus on the outer shell electrons.

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Electrophile

An atom (or group of atoms) that is attracted to an electron-rich cents or atom, where it accepts a pair of electrons to form a new covalent bond

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Electrophilic addition

A type of addition reaction in which an electrophile 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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Elimination reaction

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

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Empirical formula

The simplest whole number ratio of each element present in a compound

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Endothermic reaction

A reaction in which the enthalpy of the products is greater than that of the reactants, resulting in heat being taken in from the surroundings (delta H +ve)

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Enthalpy (H)

The heat content stored in a chemical system

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(Standard) Enthalpy change of combustion

The enthalpy change that takes place when 1 mole of substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard state

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(Standard) Enthalpy change of formation

The enthalpy change that takes place when 1 mole of substance in its standard state is formed from its constituent elements in their standard state, 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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Enthalpy cycle

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

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Enthalpy profile diagram

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

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Esterification

The reaction of an alcohol with a carboxylic acid to produce an ester and water

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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 (delta H -ve)

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Fractional distillation

The separation of the components in a liquid mixture into fractions which differ in boiling point (and hence chemical composition) by means of distillation, typically using a fractionating column

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Fragmentation

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

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Functional group

The part of an organic molecule responsible for chemical reactions

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General formula

The simplest algebraic formula of a member of a homologous series e.g. for alkanes CnH2n+2

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Giant covalent lattice

A 3-dimensional structure of atoms bonded together by strong covalent bonds

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Giant ionic lattice

A 3-dimensional structure of oppositely charged ions, held together by strong ionic bonds

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Giant metallic lattice

A 3-dimensional structure of positive ions and delocalised electrons, bonded together by strong metallic bond

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Greenhouse effect

The process in which the absorption and subsequent emission of infrared radiation by atmospheric gases warms the lower atmosphere and the planet's surface

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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 number of outer-shell electrons

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Hess' Law

If a reaction can take place by more than 1 route and the initial and final conditions are the same, the total enthalpy change is the same for each route

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Heterogeneous catalysis

A reaction in which the catalyst has different physical state from the reactants (frequently, reactants are gases and catalyst is solid)

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Heterolytic fission

The breaking of a covalent bond with both of the bonded electrons going to 1 of the atoms, forming cation (+ve) and anion (-ve)

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Homogeneous catalysis

A reaction in which the catalyst and reactants are in the same physical state (usually aqueous or gaseous)

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Homologous series

A series of organic compounds with the same organic function group, but with each successive member differing by CH2

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Hydrated

Cystalline, and containing water molecules

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Hydrocarbon

An organic compound containing hydrogen and carbon only

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Hydrogen bond

A strong dipole-dipoleattrsction between an electron-deficient hydrogen atom on one molecule and a lone pair of electrons on a highly electronegative atom of a different molecule

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Hydrolysis

A reaction with water or aqueous hydroxide ions that breaks a chemical

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Initiation

The first step in a radical substitution in which the free radicals are generated by UV radiation

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Intermolecular force

An attractive force between neighbouring molecules. Intermolecular forces can be van der Waals forces, permanent dipole-dipole forces or hydrogen bonds

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Ion

A +ely or -vely charged atom or (covalently bonded) group of atoms (a molecular ion)

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Ionic bond

The electrostatic attraction between oppositely charged ions

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Ionic pair

An outer shell pair of electrons not involved in the chemical bonding

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(First) ionisation energy

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

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(Second) ionisation energy

The energy required to remove 1 electron from each atom in 1 mole of gaseous atoms to from 1 mole of gaseous 2+ ions

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(Successive) ionisation energy

A measure of the energy required to remove each electron in turn

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Isotopes

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

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le Chatelier's principle

When a system in dynamic equilibrium is subjected to a change, the position of equilibrium will shift to minimise the change

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Limiting reagent

The substance in a chemical reaction that runs out first

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Lone pair

An outer shell of electrons that is not involved in chemical bonding

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Mass (nucleon) number

The number of particles (protons and neutrons) in the nucleus

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Mechanism

A sequence of steps showing the path taken by electrons in a reaction

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Metallic bond

The electrostatic attraction between +ve metal ions and delocalised electrons

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Molar mass, M

The mass per mole of a substance (expressed in g mol^-1)

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Molar volume

The volume per mole of a gas (expressed in dm^3 mol ^-1). At room temperature, and pressure the molar volume is approximately 24.0 dm^3 mol^-1

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Mole

The amount of any substance containing as many particles as there are in exactly 12g of the C12 isotope

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Molecular formula

The number of atoms of each element in a molecule

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Molecular ion, M+

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

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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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Nomenclature

A system of naming compounds

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Nucleophile

AN atom (or group of atoms) that 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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Nucleophilic substitution

A type of substitution reaction in which a nucleophile 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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Oxidation umber

A measure of the electrons that an atom uses to bond with atoms of another element. Oxidation numbers are derived from a set of rules

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Oxidising agent

A reagent that oxidises (takes electrons from) another species

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Percentage yield

actual amount (mol) of product / theoretical amount (mol) of product x 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 for 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 the electronegativities of the bonded atoms

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Permanent dipole-dipole force

An attractive force between permanent dipoles in neighbouring polar molecules

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Permanent dipole force

A weak attractive force between permanent dipoles in neighbouring polar molecules

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Pi-bond

The reactive part of a double bond formed above and below the plane of the bonded atoms by sideways overlap of p-orbitals

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Polar covalent bond

A bond with a permanent dipole

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Polar molecule

A molecule with an overall dipole, taking into account any dipoles across bonds

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Polymer

A long molecular chain built up from monomeric units

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Precipitation reaction

The formation of a solid from a solution during a chemical reaction. Precipitates are often formed when 2 aqueous solutions are mixed together

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Principal quantum number

n, a number representing the relative overall energy of each orbit, which increases with distance from the nucleus. The sets of orbitals with the same n value are referred to as electron shells or energy levels.

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Propagation

The 2 repeated steps in radical substitution that builds up the products in a chain reaction

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Radical

A species with an unpaired electron

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Radical substitution

A type of substitution reaction in which a radical replaces a different atom or group of atoms

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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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Redox reaction

A reaction in which both reduction and oxidation take place

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Reducing agent

A reagent that reduces (adds electrons to) another species

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Reduction

Gain of electrons or a decrease in oxidation number

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Reflux

The continual 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

The weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of C-12

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Relative formula mass

The weighted mean mass of a formula unit compared with one-twelfth of the mass of an atom of C-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 C-12

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Relative molecular mass

The weighted mean mass of a molecule compared with one-twelfth of the mass of an atom of C-12

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Repeat unit

A specific arrangement of atoms that occurs in the structure over and over again. They are included in brackets, outside of which is the symbol n

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Salt

A chemical compound formed from an acid, when a H+ ion from the acid has been replaced by a metal ion or another +ve ion (e.g. ammonium, NH4+)

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Saturated hydrocarbon

A hydrocarbon with single bonds only

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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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Simple molecular lattice

A 3-dimensional structure of molecules, bonded together by weak intermolecular forces

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Skeletal formula

A simplified organic formula, with H atoms removed from alkyl chains leaving just a carbon skeleton and associated functional groups

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Species

Any type of particle that takes part in a chemical reaction

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Specific heat capacity, c

The energy required to raise the temperature of 1g of substance by 1 degree C

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Spectator ions

Ions that are present but do not take part in a chemical reaction

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Standard conditions

A pressure of 100kPa (1 atm), a stated temperature, usually 298 K (25 deg C), and a concentration of 1 mole dm^-3 (for reactions with aqueous solutions)

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Standard solution

A solution of known concentration. Normally used in titrations to determine unknown information about another substance

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Standard state

The physical state of a substance under the standard conditions of 100 kPA and 298 K (25 deg C)

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Stereoisomers

Compounds with the same structural formula but a different arrangement of the atoms in space

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Stoichiometry

The molar relationship between the relative quantities of substances taking part in a reaction

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Stratosphere

The second layer of the Earth's atmosphere, containing the ozone layer, about 10 - 50 km above the Earth's surface

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Structural formula

A formula showing the minimal details for the arrangement of atoms in a molecule

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Structural isomers

Molecules with the same structural formula but 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 2 radicals combine to form a molecule

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Thermal decomposition

The breaking up of a chemical substance with heat into at least 2 chemical substances

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Troposphere

The lowest layer of the Earth's atmosphere, extending from the Earth's surface unto about 7 km (above the poles) and upto about 20 km (above the tropics)

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Unsaturated hydrocarbon

A hydrocarbon containing carbon-to-carbon multiple bonds

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van der Waals' forces

Very weak attractive forces between induced dipoles in neighbouring molecules

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Volatility

The ease with which a liquid turns into a gas. It increases as boiling point decreases

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Water of crystallisation

Water molecules that form an essential part of the crystalline structure of a compound

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Unit 1 (Atoms, bonds and groups) Module I: Atoms and reactions

Unit 1 Module I: Atoms and reactions

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Unit 1 (Atoms, bonds and groups) Module 2: Electrons, bonding and structure

Unit 1 Module 2: Electrons, bonding and structure

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Unit 1 (Atoms, bonds and groups) Module 3: The Periodic Table

Unit 1 Module 3: The Periodic Table

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Unit 2 (Chains, energy and resources) Module 1: Basic concepts and hydrocarbons

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Unit 2 (Chains, energy and resources) Module 2: Alcohols, halogenoalkanes and analysis

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Unit 2 (Chains, energy and resources) Module 3: Energy

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Unit 2 (Chains, energy and resources) Module 4: Resources

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Chemsitry Unit 1 and 2 definitions

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