Chemistry Definitions

Question	Answer
Acid	Species that is a Proton Donor
Activation Energy	Minimum energy required to start a reaction by the breaking of bonds
Alicyclic Hydrocarbon	Hydrocarbon with carbon atoms joined in a ring structure
Aliphatic Hydrcarbon	Hydrocarbon with carbons joined in a straight or branched chain
Alkali	A base that dissolves in water forming hydroxide ions
Atom Economy	Molecular mass of desired product -------------------------------------------------- X 100 Sum of molecular masses of all products
Atomic orbital	Region in atom which 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
Carbanion	Organic ion in which a carbon atom has a negative charge
Carbocation	Organic ion in which a carbon atom has a positive charge
Concentration	Amount of solute in mol, per 1dm3 (1000cm3) of solution: n=CxV(dm3) C=n/V(dm3)
Cracking	Breaking down of long chain saturated hydrocarbons to form a mixture of shorter chained alkanes and alkenes
Delocalised Electrons	Electrons shared between more than 2 atoms
E/Z isomerism	Type of stereo-isomerism in which different groups attached to each carbon of a C=C bond may be arranged differently in space due to restricted rotation of the C=C bond
Electron Shielding	Repulsion between electrons in different shells. Shielding reduces net attractive force from the nucleus on the outer shell electrons
Electrophilic Addition	Addition reaction Electrophile attracted to electron-rich centre or atom Accepts a pair of electrons to form a covalent bond
Empirical Formula	Simplest whole ratio of atoms of each element in a compound
Endothermic Reaction	Enthalpy of products is greater than that of the reactants resulting in heat being taken in from the surroundings
Exothermic Reaction	Enthalpy is greater in reactants than products resulting in heat being given out to surroundings
Standard Enthalpy Change of Combustion	The enthalpy change that takes place when one mole of a substance combusts completely with oxygen under standard conditions.
Standard Enthalpy change of Formation	Standard change of enthalpy when one mole of a compound is formed from its constituent elements in their standard states
Enthalpy cycle	A diagram showing alternative routes between reactants and products
Esterification	Reaction between an alcohol and c carboxylic acid to produce an ester and water
Functional group	Part of a organic molecule responsible for its chemical reactions
Giant covalent lattice	Three dimensional structure of atoms bonded together by strong covalent bonds
Giant ionic lattice	Three dimensional structure of oppositely charged ions bonded together by ionic bonds
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
Ion	A positively or negatively charged atom or (covalently bonded) group of atoms (molecular ion)
Ionic bond	Electrostatic attraction between oppositely charged ions
Le Chatelier's Principle	When a system in dynamic equilibrium is subject to change, the position of the equilibrium shifts to minimise the change
Lone pair	outer shell pair of electrons not involved in chemical bonding
Metallic Bond	Electrostatic attraction between positive metal ions and delocalised electrons
Nomenclature	system of naming compounds
Percentage Yield	Actual amount, in mol of product --------------------------------- x 100 Theoretical amount, in mol of product
Radical Substitution	Substitution reaction where a radical replaces a different atom or group of atoms
Stereoisomers	Compounds with same structural formula but with a different arrangement of atoms in space
Volatility	The ease with which a liquid turns into a gas

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	Created by Charlotte Lyon-Tiger almost 10 years ago