Chemistry definitions

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  • Created on: 08-04-14 20:45
Acid dissociation constant, Ka
Ka= (H+)(A-) / (HA)
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acid-base pair
A pair of two species that transform into each other by gain or loss of a proton.
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Activation energy
The minimum energy required to start a reaction by the breaking of bonds.
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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 by which a solid holds molecules of a gas or liquid or solute as a thin film on the surface of a soild, or liquid
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Alkali
A type of base that dissolves in water to form OH- ions
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Anion
A negatively charged ion
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Atom economy
molecular mass of desired product / sum of molecular masses of products X 100
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Atomic orbital
A region within an atom that can hold up to two electrons with opposite spins
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Average bond enthalpy
The average enthalpy change that takes place when breaking by homolytic fission 1 mol of a given type of bond in the molecules of a gaseous species.
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Avogadro's constant, Na
The number of atoms per mole of the carbon-12 isotope (6.02 x 10^23)
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Cation
A positively charged ion
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chiral carbon
a carbon atom that is attached to four different atoms, or groups of atoms.
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Complex ion
a transition metal ion bonded to one or more ligands by coordinate bonds (dative covalent bonds)
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chromatogram
a visible record showing the result of separation of the components of a mixture by chromatography.
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conjugate acid
a species formed when a proton is added to a base
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conjugate base
a specied formed when a proton is added to an acid
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coordinate bond
a shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only aka a dative covalent bond
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coordination number
the total number of coordinate bonds formed between the central metal ion and any ligands
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covalent bond
a bond formed by a shared pair of electrons
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cracking
the breaking down of a long-chained saturated hydrocarbons to form a mixture of shorter-chained alkanes and alkenes.
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delocalised electrons
electrons that are shared between more than two atoms
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dipole-dipole force
an attractive force between permanent dipoles in neighbouring polar molecules.
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disproportionation
the oxidation and reduction of the same species 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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(first) electron affinity
The enthalpy change that accompanies the addition of one electron to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions
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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.
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electronegativity
a measure of the attraction of a bonded atom for the pair of electrons in a covalent bond.
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electrophile
an atom (or group of atoms) which is attracted to an electron rich centre, 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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Enantiomers
stereoisomers that are non-superimposable mirror images of each other; aka 'optical isomers.'
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endothermic
a reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken in from the surroundings (H+ve)
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enthalpy change of atomisation
the enthalpy change that takes place when one mole of gaseous atoms forms from the element in its standard state.
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enthalpy change of combustion
the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard state.
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enthalpy change of formation
the enthalpy change that takes place when one mole of a compound in its standard state is formed from its constituent elements in their standard states under standard conditions.
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enthalpy change of hydration
the enthalpy change that takes place when one mole of isolated gaseous ions is dissolved in water, forming one mole of aqueous ions, under standard conditions.
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enthalpy change of neutralisation
the energy change that accompanies the neutralisation of an aqueous acid by an aqueous base to form one mole of H20, under standard conditions
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enthalpy change of reaction
the nthalpy 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 change of solution
the enthalpy change that takes place when one mole of a compound is completely dissolved in water under standard conditions.
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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, H
The heat content that is stored in a chemical system.
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Entropy, S
The quantitative measure of the degree of disorder in a system
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Entropy change of reaction, AS
The entropy 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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Equivalence point
The point in a titration at which the volume of one solution has reacted exactly with the volume of the second solution
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Esterification
The reaction of an alcohol with a carboxylic acid to produce and ester and water.
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Exothermic
A reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings (H-ve)
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Free energy change, AG
The balance between enthalpy, entropy and temperature for the process: AG= AH - TAS. A process can take place spontaneously when AG < 0
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Functional group
The part of the organic molecule responsible for its chemical reactions.
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Giant covalent lattice
A 3D structure of atoms, bonded together by strong covalent bonds.
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Giant ionic lattice
A 3D structure of oppositely charged ions, bonded together by strong ionic bonds.
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Giant metallic lattice
A 3D structure of positive ions and delocalised electrons, bonded together by strong metallic bonds.
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Greenhouse effect
The process in which the absorption and subsequent emission of infra-red radiation by atmospheric gases warms the lower atmosphere and the planet's surface
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Half-life
The time taken for the concentration of the reactant to reduce by half.
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Heterogeneous catalysis
A reaction in which the catalyst has a different physical state from the reactants; frequently reactants are gases whilst the catalyst is a solid.
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Heterolytic fission
The breaking of a covalent bond with both of the bonded electrons going to one atom, forming a cation and an anion
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HDL
A type of lipoprotein that can remove cholesterol from the arteries and transport it back to the liver for excretion or re-utilisation.
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Homolytic fission
The breaking of a covalent bond with one of the bonded electrons going to each atom, forming two radicals.
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Hydrogen bond
A strong dipole-dipole attraction between an electron deficient hydrogen atom on one molecule and alone pair of electrons on a highly electronegative atom on a different molecule.
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Ionic bonding
The electrostatic attraction between oppositely charged ions.
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Ionic product of water
Kw= [H+] [OH-], 1x10^-14
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(first) ionisation energy
The energy required to remove one lectron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.
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Isoelectric point
The pH value at which the amino acid exists as a zwitterion.
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Lattice enthalpy
The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions.
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Le Chateliers principle
When a system in dynamic equilibrium is subjected to a change, the system reajusts itself to minimise the effect of the change and to restore equilibrium.
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Ligand
A molecule or ion that can donate a pair of electrons with the transition metal ion to form a coordinate bond.
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Limiting reagent
The substance in a chemical reaction that runs out first
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LDL
A type of lipoprotein responsible for carrying cholesterol and triglyceries from the liver to the tissues.
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Nucleophile
An atom which 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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Percentage yield
actual amount (in mol) of product / theroretical amount (in mol) of product x 100
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pH
-log[H+]
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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 number are referred to as electron shells or energy levels.
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Rate constant
The constant that links the rate of reaction with the concentrations of the reactions raised to their orders in the rate equation.
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Rate-determining step
The slowest step in the reaction mechanism of a multi-step reaction.
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Retention time
In gas chromatography, it is the time for a component to pass from the column inlet to the detector.
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Rf value
distance moved by component/ distance moved by solvent front.
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Salt
A chemical compound formed from an acid, when an H+ ion from the acid has been replaced by a metal ion or another positive ion.
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Shell
A group of atomic orbitals with the same principle quantum number. Aka main energy level.
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Specific heat capacity
The energy required to raise the temperature of 1g of a substance by 1 degree.
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Spin-spin coupling
The interaction between spin states of non-equivalent nuclei that results in a group of peaks in an NMR spectrum.
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Stability constant
The equilibrium constant for an equilibrium existing between a transition metal ion surrounded by water ligands and the complex formed when the same ion has undergone a ligand substitution reaction.
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Standard electrode potential
The emf of a half cell compared with a standard hydrogen half cell, measured at 298K with solution concentrations of 1 mol dm-3 and a gas pressure of 1 atm.
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Stratosphere
The second layer of the Earth's atmosphere, containing the 'ozone layer' between about 10km and 50km above the Earth's surface.
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Sub-shell
A group of the same type of atomic orbitals (s,p,d,f) within a shell.
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Thermal decomposition
The breaking up of a chemical substance with heat into at least two chemical substances.
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Troposphere
The lowest layer of the Earth's atmosphere, extending from the Earth's surface up to about 7km (above the poles) to about 20km (above the tropics)
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Valence shell
the outermost shell of an atom, which contains the lectrons most likely to react and bond to other atoms.
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proton, neutron and electron relative mass and relative charge
proton= 1, +1. neutron= 1, 0. electron= 1/2000, -1
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Atomic radius
The greater the atomic mass, the smaller the nuclear attraction experienced by the outer electrons
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Nuclear charge
The greater the nuclear charge, the greater the attractive force on the outer electrons
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Electron shielding or screening
Inner shells of electrons repel the outer shell electrons, this repelling effect is called electron shielding, the more inner shells there are, the larger the shielding effect and the smaller the nuclear attraction experienced by the outer electrons.
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s orbital
from n=1 upwards, each shell contains one s-orbital. This gives a total of 1x2=2s electrons in each shell.
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p orbitals
from n=2 upwards, each shell contains three p-orbitals. This gives a total of 3x2=6 p electrons.
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d orbitals
from n=3 upwards, each shell contains five d-orbitals. This gives a total of 5x2=10d electrons
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f orbitals
from n=4 upwards, each shell contains seven f-orbitals. This gives a total of 7x2= 14 f electrons.
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Shapes
trigonal planar= 3 electron pairs, tetrahedral=4electron pairs, octahedral=6 electron pairs,
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What causes van der waal forces?
the movement of electrons in the shells unbalances the distribution of charge. There is an instantaneous dipole across the molecule. This instantaneous dipole induces a dipole in neighbouring molecules. The dipoles attract one another causing weak VD
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diamond
tetrahedral, covalent bonds, poor conductivity, hard
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graphite
strong hexagonal layer, weak van der waals, good conductivity, soft.
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A pair of two species that transform into each other by gain or loss of a proton.

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acid-base pair

Card 3

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

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Card 4

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

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Card 5

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The process by which a solid holds molecules of a gas or liquid or solute as a thin film on the surface of a soild, or liquid

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