Definitions Flashcards
Acid
A species that is a proton donor
Activation Energy
The minimum energy required to start a reaction by the breaking of bonds
Addition Polymer
A very long molecular chain formed by repeated addition reactions of many unsaturated alkene molecules (monomers)
Addition Polymerisation
The process in which unsaturated alkene molecules (monomers) add onto a growing polymer chain one at a time to form a very long saturated molecular chain (the addition polymer).
Addition Reaction
A reaction in which a reactant is added to an unsaturated molecule to make a saturated molecule.
Adsorption
The process that occurs when a gas, liquid or solute is held to the surface of a solid or, more rarely, a liquid.
1st Ionisation Energy
The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions with a single positive (1+) charge
2nd Ionisation Energy
The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions with a doublepositive (2+) charge
Alicyclic hydrocarbon
A hydrocarbon with carbon atoms joined together in a ring structure
Aliphatic Hydrocarbon
A hydrocarbon with carbon atoms joined together in a straight or branched chains
Alkali
A type of base that dissoves in water forming hydroxide ions OH- (aq) ions
Alkanes
The homologous series with the general formula CnH2n+2
Alkyl group
An alkane with a hydrogen atom removed eg. CH3, C2H5. Alkyl groups are often shown as ‘R’
Amount of Substance
Quantity whose unit is the mole. Chemists use the “amount of substance” as a means of counting atoms
Anhydrous
A substance that contains no water molecules
Anion
Negatively charged ion
Atom Economy
Atomic Orbital
A region of space in which up to two electrons can be found with opposite spins
Atomic (proton) number
The number of protons in the nucleus of the atom. The same as the number of electrons surrounding a neutrally charged atom of the element.
Average bond enthalpy
The average enthalpy change that takes place when breaking by homolytic fission 1 mole of a given type of bond in the molecules of a gaseous species
Avogadro Constant NA
The number of atoms per mole of the carbon-12 isotope (6.02 x10^23)
Base
A species that is proton acceptor
Biodegradable material
A substance that is broken down naturally in the environment by living organisms
Bolzmann Distribution
The distribution of energies of molecules at a particular temperature, usually shown as a graph.
Bond enthalpy
The enthalpy change that takes place when breaking by homolytic fission 1 mole of a given bond in the molecule of a gaseous species
Carbanion
An organic ion in which a carbon atom has a negative charge
Carbocation
An organic ion in which a carbon atom has a positive charge (Br2 mechanism)
Catalyst
A substance that increases the rate of a chemical reaction without being used up in the process.
Cation
A positively charged ion
Cis-trans isomerism
A special type of E/Z isomerism in which there is a non-hydrogen group and a hydrogen atom on each C of a C=C double bond. Cis –> H atoms are on the same side (like the Z) Trans –> H atoms are on different sides (like the E)
Compound
A substance formed from two or more chemically bonded elements in a fixed ratio, usually shown by a chemical formula
Concentration
The amount of solute, in mole, per 1 dm^3 (1000cm^3) of solution
Covalent Bond
A bond formed by a shared pair of electrons
Cracking
The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-chained alkanes and alkenes.
Curly Arrow
A symbol used in reaction mechanisms to show the movement of a pair of electrons in the breaking or formation of a covalent bond
Dative Covalent Bond / Co-ordinate bond
A shared pair of electrons which has been provided by one of the bonding atoms only.
Dehydration
An elimination reaction in which water is removed from a saturated molecule to make an unsaturated molecule
Delocalised electrons
Electrons that are shared between more than two atoms esp. found in metallic bonds
Displacement reactions
A reaction in which a more reactive element displaces a less reactive element from an aqueous solution of the latter’s ions
Displayed formula
A formula showing the relative positioning of all the atoms in a molecule and the bonds between them
Disproportionation
A special type of redox in which the same species is simultaneously oxidised and reduced at the same time.
Dynamic equilibrium
The equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the backwards reaction
E/Z isomerism
A type of stereoisomerism in which different groups attached to each carbon of the C=C double bond may be arranged differently in space because of restricted rotation of the C=C double bond.
Electron configuration
The arrangement of electrons in an atom
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
Electronegativity
The measure of the attraction of a bonded atoms 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 to form a new covalent bond
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
Elimination reaction
The removal of a molecule from a saturated molecule to make an unsaturated molecule
Empirical formula
The simplest whole number ratio of atoms of each element present in a compound
Endothermic Enthalpy Profile Diagram
Endothermic reaction
A reaction in which the enthalpy of products is greater than the enthalpy of the reactants, resulting in heat being taken in from the surrounding (ΔH = +ve)
Enthalpy cycle
A diagram showing alternative routes between reactants and products which allows the indirect determination of an enthalpy change from other known enthalpy changes using Hess’ Law
Enthalpy Formula
-q/mol
Enthalpy profile diagram
A diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products
Enthalpy, H
The heat content that is stored in a chemical system
Esterification
The reaction of an alcohol with a carboxylic acid to produce an ester and water
Ethene and Bromine Mechanism
Exothermic reaction
A reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in a heat loss to the surroundings (ΔH = -ve)
Exothermic Enthalpy Profile Diagram
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 (evaporation and condensation) by use of a fractionating column
Fragmentation
The process in mass spectrometry that causes a positive ion to split into 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 for a member of a homologous series. Eg. CnH2n+2
Giant covalent lattice
A 3D structure of oppositely charged ions bonded together by strong covalent bonds
Giant ionic lattice
A 3D structure of oppositely charged ions bonded together by strong ionic bonds (electrostatic forces of attraction)
Giant metallic lattice
A 3D structure of positive ions and delocalised electrons held together by metallic bonds with strong electrostatic forces of attraction
Greenhouse Effect
The process by which the absorption and subsequent emission of infrared radiation by atmospheric gases warms the lower atmosphere and the planet’s surface
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 which the catalyst is a solid
Heterolytic fission
The breaking of a covalent bond with both of the bonded electrons going to one of the atoms forming a cation (+ ion) and an anion (- ion)
Homogenous 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 compound with the same functional group, but with each sucessive member differing by CH2
Homolytic fission
The breaking of a covalent bond with one of the bonded electrons going to each atom, forming two radicals.
Hydrated
Crystalline and containing water molecules
Hydrocarbon
A compound of hydrogen and carbon only
Hydrogen bond
A strong dipole-dipole attraction between an electron deficient hydrogen atom (Hδ+) and a lone pair of electrons on the highly electronegative atom on a different molecule (:Oδ-)
Hydrolysis
A reaction with water or aqueous hydroxide ions that breaks a chemical compound into two chemical compounds
Initiation
The first step in a radical substitution in which the radicals are generated by ultraviolet radiation
Intermolecular forces
An attractive force between neighbouring molecules. They can be van der Waals forces (induced dipole-dipole forces), permanent dipole-dipole forces or hydrogen bonds
Ion
A positively or negatively charged atom or (covalently bonded) group of atoms (molecular ion)
Ionic bonding
The electrostatic attraction between oppositely charged ions
Isotopes
Atoms of the same element with different numbers of neutrons and hence different masses
le Chatlier’s principle
When a system in dynamic equilibrium is subjected to change, the position of the equilibrium will shift to minimise the change
Limiting Reagent
The substance in a chemical reaction that runs out first
Lone pair
An outer shell pair of electrons not involved in bonding
Mass (Nucleon) Number
The number of particles (protons and neutrons) in the nucleus
Mechanism
A sequence of steps showing the path taken by electrons in a reaction
Metallic bond
The electrostatic attraction between positive metal ions and delocalised electrons
Molar Mass M
The mass per mole of a substance. The units of molar mass are g/mol
Molar Volume
The volume per mole of gas. The units are dm^3/mol. At STP it is roughly 24dm^3/mol
Mole
The amount of substance containing as many particles as there are atoms in 12g of the carbon-12 isotope
Molecular Formula
The number of atoms of each element in a molecule
Molecular Ion M+
The positive ion formed in mass spectronomy when a molecule loses an electron
Molecule
A small group of atoms held together by covalent bonds
Monomer
A small molecule that combines with many other monomers to form a polymer.
Nomenclature
A method for naming compunds
Nucleophile
An atom (or group of atoms) that is attracted to an electron-deficient centre or atoms where it donates a pair of electrons to forma new covalent bond
Nucleophilic Substitiution
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
Oxidation
Loss of electrons or an increase in oxidation number
Oxidation number
A measure of the number of electrons that an atom uses to bond with atoms of another element. Oxidation numbers are derived from a set of rules
Oxidation Number Rules
Oxidising agent
A reagent that oxidises (takes electrons from) another species
Period
A horizontal row of elements in the Periodic table. Elements show trends across a period
Percentage Yield Formula
Periodicity
A regular periodic variation of properties of elements with atomic number and position in the periodic table
Permanent Dipole
A small charge difference across a bond resulting from a difference in electronegativities of bonded atoms
Permanent Dipole-Dipole Force
An attractive force between permanent dipoles in neighbouring molecules
Pi-bond (π-bond)
The reactive part of a double bond formed above and below the plane of the bonded atoms by sideways overlap of p-orbitals
Polar covalent bond
A bond with a permanent dipole
Polar molecule
A molecule with an overall dipole, taking into account any dipoles across bonds. Generally non-symmetrical so dipoles do not cancel out.
Polymer
A long molecular chain built up from monomer units
Precipitation Reaction
The formation of a solid from a solution during a chemical reaction. Precipitates are often formed when two aqueous solutions are mixed together
Principle Quantum number
A number representing the relative overall energy of each orbital, 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
Propagation
Second stage in radical solution. Two repeated steps in radical solution that build up the products in a chain reaction. # (means a radical dot) Eg. XH3 react with #Cl, forming #XH2 and HCl then reacting #XH2 with Cl2 to form XH2Cl and #Cl
Radical
A species with an unpaired electron
Rate of reaction
The change in concentration of a reactant or product in a given time
Redox reaction
A reaction in which both reduction and oxidation take place
Reducing Agent
A reagent that reduces (adds electrons to) another species
Reduction
Gain of electrons or a decrease in oxidation number
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
Relative Atomic Mass Ar
The weighted mean mass of an atom of an element compared to one twelfth of the mass of an atom of the carbon-12 isotope
Relative Formula Mass
The weighted mean mass of a formula unit, compared to one twelfth of the mass of an atom of the carbon-12 isotope
Relative Isotopic Mass
The mass of an atom of an isotope compared to one twelfth of the mass of an atom of the carbon-12 isotope
Relative Molecular Mass Mr
The weighted mean mass of a molecule compared to one twelfth of the mass of an atom of the carbon-12 isotope
Repeat Unit
A specific arrangement of atoms that occurs in the structure over and over again. Repeat units are included in brackets, outside of which the symbol is n
Salt
A chemical compound formed by an acid when a H+ ion from the acid has been replaced by a metal ion or another positive ion, such as the ammonium ion NH4+
Saturated Hydrocarbon
A hydrocarbon with single bonds only
Shell
A group of atomic orbitals with the same principle quantum number, n. Also known as the main energy level
Simple molecular lattice
A 3D structure of molecules bonded by weak intermolecular forces
Skeletal Formula
A simplified organic formula, with hydrogen atoms removed from alkyl chains, leaving just a carbon skeleton and associated functional groups.
Specific Heat Capacity, c
The energy required to raise the temperature of 1g of substance by 1°C. q=mcΔT
Spectator Ions
Ions that are present but take no part in a chemical reaction
Standard Conditions
A pressure of 100kPa (1 atmosphere), a stated temperature usually 298K (25°C) and a concentration of 1mol/dm^3 (if aqueous solution)
Standard Enthalpy Change of Combustion (∆Hcө)
The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactions and products being in their standard states
Standard Enthalpy Change of Formation Standard Enthalpy Change of Combustion (∆Hfө)
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
Standard Enthalpy Change of Reaction Standard Enthalpy Change of Combustion (∆Hrө)
The enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactions and products being in their standard states
Standard Solution
A solution of a known concentration. Normally used in titrations to determine unknown information about another substance
Standard State
The physical state of a substance under the standard condisitons of 100kPa and 298K (25°C)
Stereoisomer
Compounds with the same structural formula but a different arrangements of atoms in space
Stoichiometry
The molar relationship between the relative quantities of substances taking part in the reaction
Stratosphere
The second layer of the Earth’s atmosphere containing the “ozone layer” about 10km to 50km above the Earth’s surface
Structural Formula
A formula showing the minimal detail for the arrangement of atoms in a molecule
Structural Isomer
Compounds with the same molecular formula but a different structural formula
Sub-shell
A group of the same type of atomic orbitals (s,p,d or f) within a shell
Substitution Reaction
A reaction in which an atom or group of atoms is replaced with an atom or group of atoms
Sucessive Ionisation Energy
A measure of the energy required to remove each electron in turn eg. the third ionisation energy is the energy required to go from 2+ to 3+
Termination
The end step of radical substitution when two radicals combine to form a non-radical molecule
Thermal decomposition
The breaking up of a chemical substance with heat into at least two chemical substances
Troposphere
The lowest layer of the Earth’s atmosphere, extending from the Earth’s surface up to about 7km (above the poles) and to about 20km (above the tropics)
Unsaturated hydrocarbons
A hydrocarbon containing carbon-carbon multiple bonds (normally double)
van der Waals Forces
Very weak attractive forces between induced dipoles in neighbouring molecules
Volatility
The ease that a liquid turns into a gas. Volatility increases as boiling point decreases
Water of crystallisation
Water molecules that form an essential part of the crystalline structure of a compound
