Bonding

• Metallic bond


  Attraction between positive ions and delocalised electrons
• In metals, positive metal ions are packed close together in layers in a regular way. The 3d arrangement is called a lattice. The metal ions are surrounded by mobile e- which move freely within the structure
• Delocalised electron


  Free to move, not tied to a particular atom
• Giant


  Endlessly repeating
• Ionic bond


  Electrostatic attraction between oppositely charged ions
• Ionic bonding occurs between

  Metals and non metals
• Electrons are transferred from a metal to a non metal, positive and negative ions are formed. Metal atoms lose electrons to become positive, non metals gain electrons to become negative
• Boron in group 3 does not form ions, in group 4, carbon and silicon do not usually form ions, in tin Sn4+ ion is most stable but Sn2+ is also seen. Lead compounds generally contain Pb2+ but some contain Pb4+. Transition elements form more than one stable ion
• Magnesium fluoride 


  MgF2
• Ammonium


  NH4 +
• -1 ions


  OH-

  NO2 -

  NO3 -

  CN -

  HCO3 -

  HSO4 -
• -2 ions


  CO3 2-

  SO3 2-

  SO4 2-

  HPO4 2-
• -3 ions


  PO4 3-

  PO3 3-
• Covalent bond


  Shared pair of electrons
• Covalent bonding occurs between

  2 non metals, an unpaired e- from the orbital of one atom can be shared with an unpaired electron in the orbital of another atom
• H2


  H-H
• A Lone pair


  A pair of e- which is not bonded
• Molecules with double bonds

  Formed when 2 pairs of electrons are shared, e.g O2, CO2
• Triple bonds


  3 pairs of e- are shared, e.g N2, HCN
• Non octet molecules 


  The central atom does not have a noble gas electron arrangement e.g BF3, SF6
• Boron atom


  Electron deficient
• Coordinate/ dative covalent bond


  A covalent bond in which both electrons of the shared pair come from the same atom.
• Dative bond


  1. the atom that donates the electron has a lone pair
  2. the atom which accepts the e- pair is electron deficient (not have a full outer shell)
  3. they can be shown using an arrow which points from the donating atom
• Once dative covalent bonds are formed, they act as normal covalent bonds.
• Ammonium ion


  NH4 + is an example of dative bond

  NH3 + H+ -> NH4 +
• The ammonium ion is a compound ion. It contains covalent bonds between the nitrogen and the hydrogen atoms
• Other dative bonds


  H3O+

  BF3.NH3
• The shape of a molecule is determined by

  • the total number of electron pairs around the central atom
  • the number of bonding pairs of electrons
  • the number of lone pairs of electrons
• Electron Pair repulsion theory


  • pairs of electrons repel each other so they are as far apart as possible
  • lone pairs repel slightly more than bonded pairs, as they are more compact
  • the molecule or ion takes up a shape which minimises these repulsions
  • each lone pair reduces the bond angle by 2.5°
• Calculating e- pairs


  Number of e- pairs = group number of central atom + number of bonded atoms - (charge)/ 2
• Number of lone pairs = number of e- - number of bonded atoms
• 2 bond pairs

  0 lone pairs


  Linear

  180°

  BeCl2

  
• 3 bond pairs, 0 lone pairs

  Trigonal planar

  120°

  BF3

  
• 4 bond pairs, 0 lone pairs

  Tetrahedral

  109.5°

  
• 5 bond pairs, 0 lone pairs


  Trigonal bipyramid

  90° + 120°

  
• 5 bond pairs, 0 lone pairs


  Trigonal bipyramid

  90° + 120°

  
• 6 bond pair, 0 lone pairs


  Octahedral

  90°

  
• 2 double bonds, with 0 lone pairs, is linear and 180°

  e.g CO2
• 3 double bonds, 0 lone pairs, Trigonal planar, 120°, SO3
• 2 bond pairs, 1 lone pair


  V shaped

  117.5°