Definitions Flashcards
Atomic Number
Number of protons in the nucleus of an atom
Mass Number
Total number of protons and neutrons
Isotopes
Atoms with the same number of protons but different numbers of neutrons
Relative atomic mass
weighted average mass of an atom compared to 1/12th of the mass of a C-12 atom
Relative isotopic mass
weighted average mass of an atom of a particular isotope compared to 1/12th of the mass of a C-12 atom
Relative molecular mass
weighted average mass of a molecule compared to 1/12th of the mass of a C-12 atom
First Ionisation Energy
energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
Second Ionisation Energy
Energy required to remove one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions
Avogadro’s number
the number of atoms in 12 g of C-12
Empirical Formula
the simplest whole number ratio of the atoms of each element in a compound
Molecular formula
the number of atoms of each element in one molecule of a substance
ionic bond
an electrostatic force of attraction between oppositely charged ions
covalent bond
a shared pair of electron held in place by the attraction to the nuclei either side
Dative covalent bond
a shared pair of electrons where both electrons come from the same atom
Metallic bond
an electrostatic force of attraction between a cation and a sea of declocalised electrons
Electronegativity
the ability of an atom to attract a pair of electrons in a covalent bond
Polar bond
the unequal sharing of electrons in a covalent bond causing a partial positive and partial negative charge on the atoms either side
s-block element
element with its highest energy electron in an s sub-shell
p-block element
element with its highest energy electron in a p sub-shell
d-block element
element with its highest energy electron in a d sub-shell
homologous series
series of compounds with the same functional group each differing by a CH2 group from each other
Isomers
molecules with the same molecular formula but a different arrangement of atoms
Structural Isomers
Same molecular formula but different structural formula
Chain isomers
same molecular formula but a different arrangement of C atoms in the C skeleton
Positional isomers
same molecular formula but the functional group is in a different position
Functional group isomers
Same molecular formula but a different functional group
Functional group
an atom or group of atoms which give the specific physical and chemical properties to the molecule
Enthalpy Change
change in heat energy under constant pressure
Standard conditions
100 kPa and 298 K (25 oC)
Exothermic reaction
a reaction that gives out energy to the surroundings
Endothermic reaction
a reaction that takes in energy from the surroundings
Standard enthalpy of formation
enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions. All substances are in their standard states.
Standard enthalpy of combustion
enthalpy change when one mole of a substance undergoes complete combustion in excess oxygen. All substances are in their standard states.
Hess’s Law
enthalpy change of a reaction is independent of the route taken and depends only on the initial reactants and final products
Mean bond enthalpy
Enthalpy change when 1 mole of gaseous covalent bonds are broken averaged over a series of different compounds.
Activation energy
minimum energy required for a reaction to be successful. (It is the energy required to break bonds)
Rate of reaction
change in concentration of a reactant or product per second
catalyst
substance that speeds up the rate of a reaction without being used up
How catalysts work
by providing an alternative reaction pathway with lower activation energy
Dynamic Equilibrium
reaction in which both the forward and reverse reaction happen at the same rate so the concentration of reactants and products remain constant
Le Chatelier’s Principle
if a change of conditions is imposed on a system at equilibrium, the system will act to oppose the change
Oxidation
Loss of electrons. (Can also be gain of O, loss of H or increase in ox number)
Reduction
Gain of electrons. (Can also be loss of O, gain of H or decrease in ox number)
Oxidising agent
electron acceptor (the substance being reduced)
Reducing agent
electron donor (the substance being oxidised)
Stereoisomers
same molecular formula but a different arrangement of atoms in 3D space
Redox reaction
reaction in which both oxidation and reduction occur
Geometrical isomers
same molecular formula but a different spatial arrangement of atoms around a double bond
Addition reaction
Reaction in which two or more molecules combine to form a single larger molecule
Substitution reaction
reaction where one functional group is replace by another
Elimination reaction
loss of a small molecule from a larger molecule to form an unsaturated compound
Electrophile
electron pair acceptor
Nucleophile
electron pair donor
Free Radical
species with an unpaired electron
Homolytic Fission
Breaking of a covalent bond so one electron goes to each atom forming free radicals
Heterolytic Fission
Breaking of a covalent bond so both electrons go to one atom forming a cation and anion
Hydration
addition of water to a species
Hydrolysis
Use of water to break bonds
Unsaturated
Organic compound containing a C=C double bond
Saturated
Organic compound with only C-C single bonds
Addition polymerisation
Combination of a large number of monomers to form a single chain
Biofuel
Fuel produced from renewable biological resources.
