Covalent network lattices and covalent layer lattice

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Covalent network lattices and covalent layer
lattice
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3 Different types of Carbon

• Charcoal, diamond and graphite are different
  physical forms of carbon ,
• these are called allotropes of carbon.

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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.

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Other examples of covalent network lattices

• Silicon dioxide also called silica is found in
  quartz

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Covalent lattices

• Graphite is hard in two dimensions but slippery
  in another. The carbon in graphite is bonded in
  2D layers.

Weak intermolecular bonds
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Revision

• How are carbon dioxide molecules bonded together?
• With Dispersion forces
• Are Dispersion forces weak or strong?
• Weak

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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.

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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

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• c

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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

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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.

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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

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• Explain the trend in the following melting
  points.
• The trend is the increase in melting points of
  halogens down a group.
• There is an increase in the melting points
  because the strength of intermolecular forces
  increases as you go down the halogen group.
  Iodine is heavier and has more electrons and
  therefore the London forces between iodine
  molecules are stronger than those between the
  smaller fluorine molecule. Stronger
  intermolecular forces result in a higher melting
  point

Melting point (C)
Fluorine (F2) -220
Chlorine (Cl2) -101
Bromine (Br2) -7
Iodine (I2) 114
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• The mass of the HF molecule is similar to the
  mass of a neon atom, yet there boiling points is
  very different. HFs b.p. is 19.5C and Nes b.p
  is -246C. Explain this difference.

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• 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.

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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

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• How is hydrogen bonding different from a dipole
  dipole interaction?
• Pg 127 Question 13 and 15