Bonding

• 3 bp, 0 lp

  This is the shape of a molecule when it has 3 bonding pairs and 0 lone pairs.

  A) trigonal planar

  B) 120 degrees

  
• 2 bp, 0 lp

  This is the shape of a molecule when it has 2 bonding pairs and 0 lone pairs.

  A) linear

  B) 180 degrees

  
• 2bp, 1 lp

  This is the shape of a molecule when it has 2 bonding pairs and 1 lone pair.

  A) bent (v-shape)

  B) 118 degrees

  
• 4 ep, 0 lp

  This is the shape of a molecule when it has 4 bonding pairs and 0 lone pairs.

  A) 109.5 degrees

  B) tetrahedral

  
• 2ep, 2ep

  This is the shape of a molecule when it has 2 bonding pairs and 2 lone pairs.

  A) bent (v-shape)

  B) 104.5 degrees

  
• 5 ep, 0 lp

  This is the shape of a molecule when it has 5 bonding pairs and 0 lone pairs.

  A) 120 degrees

  B) 90 degrees

  C) trigonal bipyramidal

  
• 4 bp, 1lp

  This is the shape of a molecule when it has 4 bonding pairs and 1 lone pair.

  A) 119

  B) 89

  C) 89

  D) 119

  E) see-saw

  
• 3 bp, 2 lp

  This is the shape of a molecule when it has 3 bonding pairs and 2 lone pairs.

  A) 120

  B) 89

  C) trigonal planar / T shape

  
• 6 bp, 0 lp

  This is the shape of a molecule when it has 6 bonding pairs and 0 lone pairs.

  A) 90

  B) octahedral

  
• 5 bp, 1 lp

  This is shape of a molecule when it has 5 bonding pairs and 1 lone pair.

  A) 89

  B) square pyramid

  
• 4 bp, 2 lp

  This is the shape of a molecule when it has 4 bonding pairs and 2 lone pairs.

  A) square planar

  B) 90

  
• Pure ionic and covalent compounds are two extreme cases. Most compounds fall between them.
• Electronegativity

  The power of an atom to attract a pair of electrons in a covalent bond, where the distribution of electrons is not symmetrical.

  Fluorine is the most electronegative element

  Caeserium is the least electronegative element.
• Factors that effect electronegativity of an element

  • the size of the nuclear charge (across period)
  • as the size of the nuclear charge increases, electronegativity increases
  • the size of the atom (down a group)
  • as the size of the atom increases, electronegativity decreases
• Polar Covalent Bonds

  • this bond forms when the shared pair of electrons is not equally shared but is more attracted towards the more electromagnetic element
  • e.g.
  • H-Cl bond
  • H-F bond
  • O-H bond
  • the greater the electronegative difference between the atoms, the more polar the bond
• Van der Waal's forces

  • temporary dipole-dipole forces
  • the strength of these forces increases as the size of molecules increases because larger molecules have more electrons, so greater possible temporary dipoles
  • straight chain molecules have stronger forces since they can pack together closer than branched molecules (e.g. butane vs methylpropane)
• Noble Gases and Halogens

  • halogens increase boiling points because the number of electrons and molecules increases, causing bigger forces
  • Noble gases increase boiling points because they exist as single atoms and have no covalent bonds linking each other (increasing VdWs)
• Dipole-dipole forces

  • polar molecules (molecules with permanent dipoles, like HF) will also attract other molecules with permanent dipoles
  • this attraction force is generally stronger than VdW's
• Hydrogen Bonds


  • these are a special type of dipole-dipole bonds
  • these only occur when H is bonded to N, O or F
  • the bond is the attraction between a lone pair on the N, O or F to a positive H+ ion from a neighbouring molecule
  • H2O has a higher boiling point than HF due to "O" having 2 lone pairs
• Dative Covalent Bonds


  • these form when the shared pair of electrons in the covalent bond come from only one of the bonding atoms
  • these are alternatively called coordinate bonds
  • one atom must have space to accept a pair of electrons, and the other atom must have a lone pair to be donated
• 3bp, 1lp

  This is the shape of a molecule when it has 3 bonding pairs and 1 lone pair.

  A) 107 degrees

  B) trigonal pyramidal