AS LEVEL CHEM OCR

• Isotopes


  Different atomic forms of the same element. Atoms with the same number of protons but a different number of neutrons
• Relative atomic mass


  The mean mass of an atom of an element, compared to 1/12th of the mass of an atom of carbon-12
• Concentration=


  Number of moles ÷ Volume
• One mole


  6.02×10^23
• Number of moles=


  mass ÷ molar mass
• r.t.p


  25 ºC

  100 kPa (1 atm)
• Molar gas volume


  24 dm³ / mol

  One mole of any gas always has the same volume at r.t.p
• Number of moles=


  Volume (dm^3) ÷ Molar gas volume (24 dm^3 / mol)
• R- Gas constant


  8.314 J / K / mol
• Gas equation


  pV = nRT

  (Pa)(m³)(K)

  Assumes forces between molecules are negligible and the molecules have a negligible size
• Empirical formula


  The smallest whole number ratio of atoms of each element in a compound
• Molecular formula


  The actual number of atoms of each element in a compound
• Ions:

  Nitrate

  Carbonate

  Sulfate

  Hydroxide

  Ammonium

  Zinc ion

  Silver ion


  Formula:

  NO3-

  CO3²-

  SO4²-

  OH-

  NH4+

  Zn²+

  Ag+
• Acids


  Proton donors - produce H+ ions in water
• Alkalis


  Proton acceptors - produce OH- ions in water
• Acid + Base=

  Metal oxide + Acid=

  Metal hydroxide + Acid=


  Salt + Water
• Metal + Acid=


  Metal salt + Hydrogen
• Metal carbonate + Acid=


  Metal salt + Carbon dioxide + Water
• Ammonia + Acid=


  Ammonium salt
• Methyl orange


  Yellow in alkali, red in acids
• Phenolphthalein


  Pink in alkali, colourless in acids
• Oxidation number of oxygen

  Nearly always -2, except in peroxides where it is -1 and 0 in molecular oxygen
• Oxidation number of hydrogen


  Nearly always +1, except in metal hydrides where it is -1 and 0 in molecular hydrogen
• Sub-shells:

  s

  p

  d

  f


  Orbitals:

  1

  3

  5

  7
• Ionic bonding


  The electrostatic forces of attraction between oppositely charged ions
• Covalent bond


  The electrostatic forces of attraction between a shared pair of electrons and the nuclei of the bonded atoms
• Exceptions to covalent bonding

  Boron trifluoride- 6 electrons in the outer shells

  Sulfur hexafluoride- 12 electrons in the outer shells
• Dative covalent bonding (coordinate bonding)


  Both electrons from one atom
• Shape of methane molecule


  No lone pairs

  Bond angle- 109.5º

  
• Shape of ammonia molecule

  1 lone pair

  Bond angle- 107º

  
• Shape of water molecule

  2 lone pairs

  Bond angle- 104.5º

  
• Linear molecules


  2 electron pairs around central atom

  Bond angle- 180º

  
• Trigonal planar


  3 electron pairs around central atom

  No lone pairs

  Bond angle- 120º

  
• Tetrahedral


  4 electron pairs around central atom

  No lone pairs

  Bond angle- 109.5º

  
• Pyramidal


  4 electron pairs around central atom

  1 lone pair included

  Bond angle 107º

  
• Nonlinear


  4 electron pairs around central atom

  2 lone pairs

  Bond angle- 104.5º

  
• Trigonal bipyramidal


  5 electron pairs around central atom

  No lone pairs

  Bond angle- 120º, 90º

  
• Octahedral


  6 electron pairs around central atom

  No lone pairs

  Bond angle- All 90º

  
• Electronegativity


  An atom's ability to attract the electron pair in a covalent bond
• Three types of intermolecular forces


  Induced dipole-dipole

  Permanent dipole-dipole interactions

  Hydrogen bonding