Chemistry AS Level AQA Physical Chemistry Revision Key Words

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Activation energy
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The minimum energy that a particle needs in order to react
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Atom economy
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mass of desired products/total mass of reactants x 100
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Atomic orbital
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A region of space where there is a high probability of finding an electron
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Avogadros constant
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The total number of particles in one mole of a substance or 6.022 x 10^23
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Catalyst
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A substance that alters the rate of a chemical reaction but is not used up in the reaction
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Carbocation
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An organic ion in which one of the carbon atoms has a positive charge.
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Co-ordinate bonding
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Covalent bonding in which both the electrons in the bond comes from one of the atoms in the bond.
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Covalent bonding
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Describes a chemical bond in which electrons are shared between two atoms
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Delocalised electrons
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Electrons that are spread over several atoms and help to bond them together
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Dipole-dipole forces
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An intermolecular force that results from the attraction between molecules with permanent dipoles
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Displayed formula
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The formula of a compound drawn out so that each atom and each bond is shown
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Electron pair repulsion theory
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Pairs of electrons around a central atom repel each other equally taking up positions as far away as possible from each other
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Electronegativity
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The power of an atom to attract a pair of electrons in a covalent bond
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Electrostatic forces
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The forces of attraction and repulsion between electrically charged particles
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Empirical formula
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The simplest whole number ratio in which the atoms in a compound combine together
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Endothermic
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Where heat is taken during a reaction and the temperature drops
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Exothermic
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Where heat is given out during a reaction and the temperature rises
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Hydrogen bonding
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Where a hydrogen atom covalently bonded to an Nitrogen, Oxygen or Fluorine atom interacts with another Nitrogen, Oxygen or Fluorine atom
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Incomplete Combustion
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A combustion reaction in which there is insufficient oxygen
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Ionic bonding
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A chemical bond in which electrons are transferred from atom to another, forming oppositely charged ions with electrostatic forces of attraction between them
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Ionisation energy
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The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole unipositive gaseous ions
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Lattice
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A regular three dimensional arrangement of atoms, ions or molecules
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Lone pair
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A pair of electrons in the outer shell of an atom that is not involved in bonding
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Metallic bonding
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A chemical bond in which outer electrons are spread over a lattice of metal ions in a delocalised system.
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Mole
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A quantity of a substance that contains the Avogadro constant (6.022×10^23) of particles
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Molecular formula
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A formula that tells us the numbers of atoms of each different element that make up a molecule
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Molecular ion
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A molecule of the sample which has been ionised but which has not broken up
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Nucleons
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Protons and neutrons
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Nucleus
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Positively charged centre of an atom composed of protons and neutrons
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Percentage yield
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The actual amount of product produced divided by the theoretical amount expressed as a percentage
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Periodicity
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The trends in the periodic table
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Polar
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A molecule where one side is slightly positively charged and the other side slightly negatively charged
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Proton number
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The number of protons in the nucleus of an atom
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Relative atomic mass
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The weighted average mass of all the isotopes of an element relative to one twelfth the mass of one atom of carbon-12
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Relative formula mass
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The average mass of a compound relative to one twelfth the mass of one atom of carbon-12
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Relative molecular mass
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The average mass of a molecule relative to one twelfth the mass of one atom of carbon-12
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Strong nuclear force
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The force that holds the protons and neutrons together within the nucleus of an atom
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van der Waals force
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a type of intermolecular force of attraction that is caused by instantaneous dipoles and acts between all atoms and molecules

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