AS CHEM2 Definitions

Key definitions

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  • Created by: Kiran
  • Created on: 18-06-11 22:21
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A LEVEL CHEMISTRY - SOME DEFINITIONS TO LEARN
ISOTOPE Atoms with ... the same atomic number but different mass number or
the same number of protons but different numbers of neutrons
ATOMIC NUMBER The number of protons in the nucleus of an atom
MASS NUMBER The sum of the protons and neutrons in the nucleus of an atom
RELATIVE ATOMIC MASS The mass of an atom relative to that of the carbon 12 isotope having a value of 12.000
EMPIRICAL FORMULA The simplest, whole number, ratio of elements in a compound
MOLECULAR FORMULA The exact number of atoms of each element in the formula of a compound
IONIC BOND Oppositely charged ions held together in a crystal lattice by electrostatic attraction
COVALENT BOND A shared pair of electrons, one electron being supplied by each atom either side of the bond
DATIVE COVALENT (CO-ORDINATE) BOND A shared pair of electrons, both electrons being supplied by one atom in the bond
ELECTRONEGATIVITY The ability of an atom to attract the pair of electrons in a covalent bond to itself
MACRO (GIANT) MOLECULE Many atoms joined together in a regular array by a large number of covalent bonds
POLAR BOND A covalent bond where the shared pair of electrons is displaced to one end
FAJAN'S RULES A compound is more likely to be covalent if the ... cation has a small size and a high charge
anion has a large size and a high charge
FIRST IONISATION ENERGY The energy required to remove one mole of electrons (to infinity) from one mole of gaseous atoms to form one
mole of gaseous positive ions.
ELECTRON AFFINITY The enthalpy change when one mole of gaseous atoms acquires one mole of electrons (from infinity) to form
one mole of gaseous negative ions.
STANDARD ENTHALPY OF FORMATION The enthalpy change when one mole of a compound is formed in its standard state from its elements in their standard states
STANDARD ENTHALPY OF COMBUSTION The enthalpy change when one mole of a substance undergoes complete combustion in its standard state
BOND (DISSOCIATION) ENTHALPY The energy required to break one mole of gaseous bonds to form gaseous atoms
STANDARD ENTHALPY OF ATOMISATION The enthalpy change when ONE MOLE of gaseous atoms is formed from an element in its standard state
ENTHALPY OF FORMATION The enthalpy change when one mole of a compound is formed in its standard state from its elements in their standard states
LATTICE DISSOCIATION ENTHALPY The enthalpy change when ONE MOLE of an ionic lattice dissociates into isolated gaseous ions
LATTICE FORMATION ENTHALPY The enthalpy change when ONE MOLE of an ionic lattice dissociates is formed from its isolated gaseous ions
ENTHALPY OF HYDRATION The enthalpy change when ONE MOLE of gaseous ions dissolves in (an excess of) water
ENTHALPY OF HYDROGENATION The enthalpy change when ONE MOLE of double bonds is reduced to single bonds by reacting with gaseous hydrogen.
HESS'S LAW The enthalpy change of a reaction is independent of the path taken

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