Covalent network lattices and covalent layer lattice by jpUEpqbo

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									Covalent network lattices
and covalent layer lattice
  3 Different types of Carbon
• Charcoal, diamond and graphite are
   different physical forms of carbon ,
 these are called allotropes of carbon.
   Covalent Network Lattice
• The carbon in Diamond is bonded very
  strongly in a 3D lattice making it hard and
  crystalline with a very high melting point.
    Other examples of covalent
         network lattices
• Silicon dioxide also called silica is found in
  quartz
          Covalent lattices
• Graphite is hard in two dimensions but
  slippery in another. The carbon in graphite
  is bonded in 2D layers.




                                        Weak
                                        intermolecular
                                        bonds
              Revision
• How are carbon dioxide molecules bonded
  together?
• With Dispersion forces
• Are Dispersion forces weak or strong?
• Weak
Properties of covalent molecular,
   network and layer lattices
• You can use the covalent molecular,
  network and lattice models to explain
  properties of non- metal compounds.
     Melting and boiling points
• When a substance melts the particles break
  out of their position (the intermolecular forces
  have been overcome).
• For small molecules, the intermolecular
  forces are weak and therefore its does not
  take a lot of energy to overcome these forces,
  making melting and boiling points low
• Network and layer lattices have high m.p. and
  b.p. because they covalent bonding
  throughout the lattices are very strong
c
      Electrical conductivity
• In Covalent molecular substances and
  covalent network lattices the electrons are
  localised and therefore cannot move
• Graphite has one electron from each
  carbon delocalised and therefore these
  are able to carry and electric current
        Chemical reactivity
• Chemical reactivity is how well a
  substance reacts with other substances
• Covalent network lattices and covalent
  layer lattices are very unreactive because
  they have such strong bonds
• Small molecular substances are more
  reactive because their bonds are not as
  strong.
     Hardness and softness
• Covalent network lattices are very hard
  because they have strong covalent bonds
  and atoms are held in fixed positions
• In covalent layer lattices the forces between
  layers are weak and layers can slide over
  one another
• The intermolecular forces in Covalent
  molecular substances determines whether
  they will be hard or not
• Because intermolecular forces are quite
  weak covalent molecular substances tend to
  be gases and liquids
• Explain the trend in the following
  melting points.
                                                  Melting
• The trend is the increase in melting
  points of halogens down a group.                point (C)
• There is an increase in the melting    Fluorine -220
  points because the strength of         (F2)
  intermolecular forces increases as
                                         Chlorine -101
  you go down the halogen group.
  Iodine is heavier and has more         (Cl2)
  electrons and therefore the London     Bromine -7
  forces between iodine molecules        (Br2)
  are stronger than those between
  the smaller fluorine molecule.         Iodine   114
  Stronger intermolecular forces         (I2)
  result in a higher melting point
• The mass of the HF molecule is similar to
  the mass of a neon atom, yet there boiling
  points is very different. HF’s b.p. is 19.5C
  and Ne’s b.p is -246C. Explain this
  difference.
• At room temperature , CCl4 is a liquid whereas
  CH4 is a gas. Why is this the case?
• Both are tetrahedral, non polar covalent
  molecules so London forces occur between the
  molecules. The London forces between CCl4 are
  stronger than CH4. This is due to CCl4 being a
  larger or heavier molecule making the london
  forces stronger making it a liquid at room
  temperature.
    As a group create a concept
   map using the following words
Polar Bond Non-polar bond Dispersion Forces
Ionic Bonding Covalent Bonding Metallic
  Bonding
Intermolecular Forces Intramolecular Forces
Polar Molecule           Non-polar Molecule
Partial Positive            Partial Negative
Dipole Dipole Forces Covalent network lattice
Hydrogen Bonding Covalent layer lattices
• How is hydrogen bonding different from a
  dipole dipole interaction?
• Pg 127 Question 13 and 15

								
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