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relative atomic mass
the average mass of an atom, taking into account the abundance of all the naturally occurring isotopes, compared to 1/12th of the mass of a carbon-12 atom
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relative molecular mass
the average mass of a molecule compared to 1/12th of the mass of a carbon-12 atom
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group
a vertical column of elements on the periodic table with similar chemical properties and the atoms have same valence shell electron configuration
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period
a horizontal row of elements on the periodic table, across a period from left to right successive atoms have one extra proton and one extra electron in the same outer shell
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molecular formula
the formula of a molecule that shows the actual number of each type of atom in the molecule
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empirical formula
the formula of a compound that shows the lowest whole number ratio of each type of atom
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isotopes
atoms of the same element with the same number of protons but a different number of neurtrons
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orbital
a region of space in which the probability of finding an electron is greater than or equal to 95%; each orbital can hold a maximum of two electrons with opposite spin
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continuous spectrum
an emission spectrum that has all frequencies of visible light
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line spectrum
an emission spectrum that has only certain frequencies of visible light that appear as colored lines
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ionic bonding
the electrostatic force of attraction between oppositely charged ions arranged in a regular 3D structure called an ionic lattic
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covalent bonding
a shared pair of electrons that holds two atoms together
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dative (coordinate) covalent bond
a shared pair of electrons that holds two atoms together and both electrons come form one atom
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sigma bond
the 'head on' overlap of two orbitals along the inter-nuclear axis
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pi bond
parallel p-orbitals overlap 'sideways on' above and below the inter-nuclear axis
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hybridization
the mixing of atomic orbitals to form the same number of new orbitals which are equal in energy to one another
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free radical
a species with one or more unpaired electron
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resonance
occurs when one or more valid Lewis structures can be drawn for a molecule or ion and the electrons are delocalized so that they are arranged in an average of the possible Lewis structures
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delocalisation
a stable bonding arrangement in which electron pairs are not confined to two adjacent bonding atoms but extend over three or more atoms
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hydrogen bond
a strong intermolecular force of attraction between a delta plus hydrogen and a lone pair of electrons on a very electronegative atom such as F, O, or N
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Van der Waals' forces
a weak intermolecular force of attraction that acts between non-polar molecules in the solid and liquid state
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electronegativity
a measure of the ability of an atom to attract a bonding pair of electrons
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polar bond
a bond in which the electrons are not equally distributed between the two atoms in the bond; the more electronegative atom will have the greater electron density
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ligand
a species that uses a lone pair of electrons to form a dative covalent bond with a central metal ion to form a complex
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periodicity
repeating pattern of physical and/or chemical properties of elements or their compounds as a function of their arrangement in the periodic table
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endothermic reaction
a reaction in which heat energy is absorbed from the surroundings causing the temperature to drop
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exothermic reaction
a reaction in which heat energy is released to the surroundings causing the temperature to increase
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standard enthalpy of reaction
the enthalpy change of a reaction using the amounts of reactants in a specified stoichiometric equation under standard conditions (298K, 101.3KPa)
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standard state
a reference state for a particular substance under standard thermodynamic conditions (298K, 101.3KPa, 1moldm-3)
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standard enthalpy of formation, ΔHfθ
the energy change when one mole of compound if formed from its elements in their standard states under standard conditions (298K, 101.3KPa)
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standard enthalpy of combustion
the energy released when one mole of a compound is completely burned in excess oxygen under standard conditions with no change in pressure
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bond enthalpy
the energy needed to break 1 mol of a specific covalent bond between two atoms in a molecule in the gaseous state averaged over several similar compounds
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first ionization energy
the energy needed to remove one mole of the highest energy electrons from one mole of neutral atoms in the gaseous state under standard conditions (298K, 101.3KPa)
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lattice enthalpy
energy released when 1 mole of a solid ionic compound is formed from its constituent ions in the gaseous state under standard conditions (298K, 101.3KPa)
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enthalpy of electron affinity
the energy released when one mole of electrons are added to one mole of atoms in the gaseous state under standard conditions (298K, 101.3KPa)
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activation energy
the minimum energy needed for the reactants to react upon collision / the difference in energy between the reactants and transition state
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catalyst
a substance that increases the rate of reaction by providing an alternative reaction pathway with a lower activation energy and it is not consumed in the overall reaction
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heterogenous
usually applied to a catalyst; in a state or phase different to the reactants
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standard entropy, Sθ
a quantity that is related to the disorder or randomness of particles of an element or compound in its standard state at 298K
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spontaneous reactions
occur when the reactants are mixed together under standard conditions (298K, 101.3KPa, 1moldm-3 solutions)
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rate of reaction
the increase or decrease in concentration, mass, or volume of reactant with time
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rate constant, k
an experimentally determined constant of proportionality that relates rate of reaction, at a particular temperature, to the concentration of the species that are involved in the reaction
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order of reaction
the power of an individual concentration term in the rate expression
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overall order of reaction
the sum of the powers of concentration terms in the rate expression
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rate determining step
the slowest step of a reaction
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molecularity
the number of particles in the slowest, rate determining step of the reaction / the number of particles participating in an elementary step of the mechanism
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half life
the time taken for the concentration of a reagent to decrease to half its original value
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chemical equilibrium
a chemical reaction is in equilibrium when the rate of the forward reaction is equal to the rate of the reverse reaction and the concentrations of the reactants and products do not change
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equilibrium constant, kc
the value obtained when the equilibrium concentration of the products are multiplied together and divided by the equilibrium concentration of the reactants multiplied together and all concentrations are raised to the power of their stoichiometric coefficients from the balanced equation
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Bronsted-Lowry acid
a specie that donates a proton
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Lewis acid
a specie that accepts an electron pair
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Bronsted-Lowry base
a specie that accepts a proton
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Lewis base
a specie that donates an electron pair
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weak acid
an acid that partially dissociates in solution
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strong acid
an acid that fully dissociates in solution
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conjugate acid-base
a pair of species whose formula differ by H+
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buffer solution
a solution that resists change in pH when small amounts of acid or alkali are added, usually made from a weak acid and a salt of its conjugate base or a weak base and a salt of its conjugate acid
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monoprotic acid
a specie with one replaceable hydrogen atom permolecule
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diprotic acid
a specie with two replaceable hydrogen atom permolecule
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equivalence point
the point in an acid-base titration when the acid and base are present in stoichiometric amounts and all the acid and base has been reacted; it is not necessarily at pH 7
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end point
when an indicator changes color suddenly during a titration and both the acidic and basic forms of the indicator are present in equal concentration
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oxidation
when a specie loses electrons / when the oxidation number of an element increases
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reduction
when a specie gains electrons / when the oxidation number of an element decreases
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oxidizing agent
a species that causes oxidation by gaining (an) electron(s) from other species and is itself reduced
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reducing agent
a species that causes reduction by donating (an) electron(s) to other species and is itself oxidized
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disproportionation
the simultaneous oxidation and reduction of atoms of a single chemical element in a reaction
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standard electrode potential
the potential difference measured under standard conditions (298K, 101.3KPa, 1moldm-3 solutions) when a half cell is connected to a standard hydrogen electrode
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hydrocarbon
a compound containing hydrogen and carbon only
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saturated
molecules that contain only carbon-carbon single bonds
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unsaturated
molecules that contain at least one carbon-carbon multiple bond
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dehydration
the removal of hydrogen and oxygen from a compound in a 2:1 atomic ratio, respectively
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homologous series
a family of compounds with the same general formula where successive members differ by one CH2 group
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nucleophilic substitution
the replacement of an atom or group within a molecule, by a species with a lone pair of electrons, which is attracted to an electron deficient part of the molecule
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isomers
forms a compound with the same molecular formula but different structural formula
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stereoisomerism
Compounds with the same molecular formula and structural formula but different arrangements of atoms in space. There are two types of stereoisomerism: geometrical and optical.
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geometrical isomerism
a type of isomerism that occurs when particular atoms or groups are joined to atoms at each side of a bond that has restricted rotation
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chiral carbon
a carbon atom that has four different groups attached causing the molecule and its mirror image to be non-superimposable
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optical isomerism
a type of isomerism that occurs when a molecule has no plane of symmetry and can exist in left and right handed forms that are non-superimposable mirror images of each other
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enantiomer
a molecule that has no plane of symmetry and is non-superimposable on its mirror image
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condensation reaction
when two small molecules combine to form a larger one with the elimination of a smaller molecule (such as water)
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addition polymerisation
process in which a large number of unsaturated monomers combine to form a polymer without the elimination of any atoms or molecules
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nucleophile
negatively charged or neutral species containing an electron pair that is attracted to and can form a covalent bond to electron deficient (delta plus) atom in another molecule
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functional group
an atom or group of atoms responsible for the characteristic reaction of the molecule or homologous series
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