AS1 chemistry definitions.

• Molar mass

  The mass of one mole of a substance
• Hydrated (salt)

  A salt which contains water of crystallisation
• Atomic number

  The number of protons in (the nucleus of) an atom
• Second ionisation energy


  The energy required to convert one mole of gaseous ions with a single positive charge into gaseous ions with a double positive charge
• Relative molecular mass (RMM)

  The average (weighted mean) mass of a molecule relative to one-twelfth of the mass of an atom of carbon-12
• Relative atomic mass (RAM)

  The average (weighted mean) mass of an atom of an element relative to one-twelfth of the mass of an atom of carbon-12
• Isotopes

  Atoms which have the same atomic number but a different mass number (contain the same number of protons but a different number of neutrons)
• Permanent dipole-dipole attraction

  Attraction between the positive end, δ+, of the permanent dipole on a molecule with the negative end, δ-, of the permanent dipole of a neighbouring molecule
• Reduction

  Gain of electrons/Decrease in oxidation state
• Intermolecular

  Between neighbouring molecules (as opposed to intramolecular)
• Polar bond

  A covalent bond in which there is unequal sharing of the bonding electrons
• Octet rule

  When reacting, an atom tends to gain, lose or share electrons to achieve eight in its outer shell
• Covalent bond

  The electrostatic attraction between a shared pair of electrons and the nuclei of bonded atoms
• Reducing agent

  Electron donor
• Redox

  Oxidation and reduction occur in the same reaction
• Strong acid/base

  Fully dissociates in solution
• Molarity

  Concentration in mol dm-3 expressed using M
• Standard solution

  A solution for which the concentration is known
• Molecular ion

  Two or more atoms covalently bonded with an overall charge
• Anhydrous (salt)

  A salt which contains no water of crystallisation
• Water of crystallisation

  Water chemically bonded within a crystal structure
• Mole

  The amount of substance which contains the Avogadro constant of atoms, molecules or groups of ions
• Electronegativity

  The extent to which an atom attracts the bonding electrons in a covalent bond
• Relative formula mass (RFM)

  The average (weighted mean) mass of a formula unit relative to one-twelfth of the mass of an atom of carbon-12
• Relative isotopic mass (RIM)

  The mass of an atom of an isotope of an element relative to one-twelfth of the mass of an atom of carbon-12
• Mass number

  The total number of protons and neutrons in (the nucleus of) an atom
• Co-ordinate (Dative) bond

  A shared pair of electrons between two atoms. One atom provides both electrons
• First ionisation energy

  The energy required to convert one mole of gaseous atoms into gaseous ions with a single positive charge
• Delocalised electrons

  Outer electrons do not have fixed positions but move freely
• Third ionisation energy

  The energy required to convert one mole of gaseous ions with a double positive charge into gaseous ions with a triple positive charge
• Hydrogen bond


  The attraction between a lone pair of electrons on a very electronegative atom (i.e. N,O, F) in one molecule and a hydrogen atom in a neighbouring molecule, in which the hydrogen atom is covalently bonded to a very electronegative atom (N,O,F)
• van der Waals’ forces

  The attraction between instantaneous and induced dipoles on neighbouring molecules
• Disproportionation

  Oxidation and reduction of the same element in the same reaction
• Oxidising agent

  Electron acceptor
• Oxidation


  Loss of electrons/Increase in oxidation state
• Concentration

  Number of moles or mass present in a stated volume
• Weak acid/base

  Partially dissociates in solution
• Avogadro constant

  Number of atoms in 12.000g of carbon-12