Chemical Bonding and Physical properties

• What three factors should we be able to predict of a molecule?

  a) melting and boiling points

  b) solubility

  c) electrical conductivity
• Giant Ionic Lattice


  Regular 3D arrangement of positive and negative ions.
• What is the melting and boiling point like ionic compounds and why?

  - Have a really high MP + BP

  - network of strong ionic bonds requires large amounts of energy to break down.
• What is the solubility of giant ionic lattices like and why

  - Giant ionic compounds are usually soluble in polar

  solvents such as water.

  - because the water molecules can break up the

  lattice, + surround the ions to form a solution
• Conductivity of solid giant ionic lattices like and why

  - don't conduct electricity as ions are fixed in place and can't move.
• Conductivity of molten / aqueous giant ionic lattices like and why


  Giant ionic compounds Conduct when molten / in aqueous solution because ions now free to move
• Giant Covalent Structure


  Structure with strong covalent bonds throughout.
• Simple Molecular Substance


  Small covalently bonded molecules held by weak intermolecular forces.
• Metallic bonding DEFINITION


  electrostatic force of attractionbetweenpositive metalionsanddelocalised electrons
• Labelled diagram of bonding in Mg+

  
• EXAM Q TIP: What two things should you include when drawing labelled diagram of metallic bonding? (3)

  - Metal with CORRECT ION CHARGE (Eg: Mg = 2+)

  - LABELS which show metal and delocalised electron

  - electrons surrounding metal with (e-) symbol
• Physical Properties of metals

  - good conductors of electricitybecause delocalised electrons can move through the lattice.

  -electrostatic attraction btw. delocalised electronsand thepositive metal ions are strongtherefore havehigh melting and boiling points
• Which metal is exception to usual physical properties of metals?

  Mercury (liquid at RTP)
• what are the allotropes of carbon?

  diamond, graphite, graphene, fullerenes (buckminsterfullerene)
• Graphene


  Single layer of graphite with strong covalent bonds between carbon atoms.
• Solubility


  Ability of a substance to dissolve in a solvent.
• Diamond Structure


  Each carbon atom covalently bonded to 4 others in a tetrahedral structure.
• Graphite Structure


  - strong covalent bonds within layers as Carbon atoms bonded in rings of 6, with delocalised electrons between layers.

  - Have weak london forces between layers
• Diamond shape and bond angle around one carbon atom?

  - shape = Tetrahderal

  - bond angle = 109.5
• Graphite shape and bond angle around one carbon atom?

  - shape = trigonal planar

  - bond angle = 120
• 3 differences btw diamond and graphite?

  - In diamond each C atom is covalently bonded to 4 other C atoms to make a giant tetrahedral structure.

  
  

  - In graphite each C is covalently bonded to 3 other C atoms in a trigonal

  planar arrangement (this uses 3 of carbons outer shell electrons).

  - The carbons are bonded together in rings of 6 to make planar hexagonal

  layers.

  
  

  - The fourth electron is free to move + is delocalised.

  - The delocalised electrons are found btw. the layers.
• Melting point of diamond

  High

  
  

  Strong covalent bonds between c atoms. High temperatures required to break bonds.

  
  

  Giant structure
• Melting point of graphite

  High

  
  

  Strong covalent bonds between c atoms. High temperatures required to break bonds.

  
  

  Giant structure
• what is the Electrical Conductivity of diamond like?

  NO CONDUCTIVITY

  
  

  All four electrons are used in

  bonding. No free moving ions or delocalized electrons.
• what is the Electrical Conductivity of graphite like?


  THERE IS CONDUCTIVITY

  
  

  3 electrons used in bonding but one is delocalised (between layers).

  
  

  Delocalized electrons are free to move and carry charge.
• what is solublity of diamond and graphite like?

  Low

  
  

  Insoluble in almost all solvents.

  Solvent cannot break apart lattice of strong covalent bonds.
• Silicon is in the same group as carbon but does not normally conduct electricity.

  Atoms arranged in tetrahedral structure. All outer shell electrons used in bonding no delocalised electrons available to move and carry charge
• Explain these physical properties of graphene?:

  - MP / BP

  - Conductivity

  - Strength


  - MP / BP = high - need to break strong covalent bonds

  
  

  - Conductivity - can conduct -> Only uses 3 outer shell electrons in bonding so fourth

  electron is delocalised.

  
  

  - Strength - Very strong. Strong covalent bonds between carbon atoms in

  hexagonal layers.
• NaCl Giant Ionic Compound

  Compound with high melting point due to strong ionic bonds.
• Strength of Graphene


  Very strong due to strong covalent bonds in hexagonal layers.
• what are Simple molecular lattices?

  Regular arrangement of particles in solid covalent compounds.
• Explain Group 7 boiling point trend?

  Boiling point increases down the group due to:

  - Increased no. e-

  - Larger induced dipoles

  - stronger London forces which require more energy to overcome
• why does increasing no. e- increase boiling point?

  - Increased no. e- causes Larger induced dipoles

  - therefore stronger London forces which require more energy to overcome
• EXAM Q STYLE TIP: When comparing two covalent molecules, what two properties should you talk about? (2)

  - They are held by STRONG covalent bonds

  - Point out which type of intermolecular force they have
• Relative strengths of bonds

  Comparison of bond strengths: - ionic/covalent (1000),

  - hydrogen bond (50)

  - dipole-dipole (10),

  - London forces (1).
• Is ice less dense than water, explain why?

  - Ice is less dense than liquid water

  - due to hydrogen bonds forming an open lattice structure when water freezes

  - there is lots of space in the structure which gives ice a lower density than water
• what can the Hydrogen bonds in water do?

  Cause high surface tension and viscosity by holding water molecules together.
• why does High surface tension of water occur in water

  Due to strong hydrogen bonds across the surface holding molecules together.
• How should the melting point of water be described when compared to other molecules? and why is this the case?

  RELATIVELYhigher

  - Because hydrogen bonds are extra forces alongside london's forces in water- Strong H-bonds need more energy to be broken down than molecules which do not have H-bonds
• Hydrogen bonding effect


  Increases boiling point and requires more energy to overcome than other intermolecular forces.