Structure and Bonding

• Group 0

  Full outer shell, do not need to form ions, stable, unreactive
• Why do elements react?

  To form a full outershell
• Ionic bonding

  Bonding between a metal and non-metal
• Metals

  Lose electrons - become positive
• Non-metals

  Gain electrons - negative charge ion
• Ion

  A charged particle - either +ve or -ve
• group 1 metals

  Lose 1 electron to gain a full outer shell, eg they react with group 7 only
• Group 7 metals

  Have a charge of 1-/need to gain 1 electron to have a full outer shell eg they react with group 1 only
• Group 2 metals

  Have a charge of 2+/ need to lose 2 electrons to gain a full outer shell eg they react with group 6 only
• Group 6 metals

  Have a charge of 2-/need to gain 2 electrons to have a full outer shell eg They react with group 2 only
• Ionic compounds

  They form a giant ionic lattice (where every every negative ion is surrounded by a positive ion and vice versa) which are 3D structure - have strong electrostatic forces of attraction which hold the ions in place
• Ionic compounds (2)

  1. VERY HIGH melting and boiling points eg 800C due to the strong electrostatic forces of attraction (takes a lot of energy to break it)
  2. Cannot conduct electricity when solid due to ions being locked in place, can vibrate, cannot move
• When can metals conduct electricity and why?

  When molten and this is due to the ions being able to move due to the heat energy breaking the forces between the ions and they can now carry the electrical charge
• Covalent bonding

  When two non-metals bond together, there share one or more pairs of electrons
• Hydrogen

  2 atoms of hydrogen bonded, both non metals, must be bonded together to have a full outer shell, the 2 electrons overlap their energy shells
• A covalent bond is a strong bond
• How can covalent bonding be shown?

  energy level diagram

  dot and cross diagram

  stick diagram
• Only covalent bonds use energy level diagrams
• Double covalent bond is shown with two lines like an = sign
• Small covalent molecules

  LOW melting and boiling point - (gases and liquid at room temp.) This is due to the weak intermolecular forces holding the molecules together - it doesn't require much energy to turn the molecules from liquid to gas
• Covalent bonds are not broken when a substance melts or boils - and as we increase the size of the molecules the intermolecular forces INCREASE
• Small covalent molecules (2)

  DO NOT conduct electricity because they do not have an overall electric charge
• Giant covalent structures

  ALWAYS SOLID AT ROOM TEMPERATURE - they all have high boiling and melting point. Strong intermolecular forces- requires a lot of energy to overcome
• Diamond

  Formed from CARBON - has 4 electrons on outer shell, to gain a full outer shell EACH CARBON ATOM FORMS COVALENT BONDS TO FOUR OTHER CARBON ATOMS - very hard due to millions of bonds - high melting and boiling point - doesn’t conduct electricity, ions can’t move, can’t carry the charge
• Silicon Dioxide

  Silicon and Oxygen covalently bonded - lots of covalent bonds - very high melting and boiling point
• Graphite

  very high melting and boiling point; GOOD conductor of electricity; Each carbon‘s covalently bonded to 3 other carbon atoms and forms a layer of hexagonal rings
• Graphite (2)

  no covalent bonds between the layers so it is Soft and slippery/slide over each other - often used in lubricants which reduces friction
• Graphite (3)

  each carbon atom has one electron in its outer shell which isn’t in a covalent bond - they are released from the carbon atom - DELOCALISED ELECTRONS - can move so can conduct heat and electricity
• GRAPHITE IS NOT A METAL
• Graphite is formed from layers of carbon atoms in hexagonal rings
• Graphene

  Single layer of graphite - one atom thick - good conductors of electricity - extremely strong
• Fullerenes


  Molecules of carbon atoms with hollow shapes - hexagonal rings with 5 or 7 carbon atoms
• Buckminsterfullerene (C60)


  Spherical, hollow shape - form 6 or 5 carbon atom Rings
• Uses of fullerenes

  Pharmaceutical delivery - lubricants - catalysts
• Carbon nanotubes

  Fullerenes shaped into long cylinders - 6-carbon-atom ring; high tensile strength (stretched without breaking); good conductor of heat and electricity; used to reinforce materials like in tennis rackets
• Polymers


  Made by joining thousands of identical small molecules (monomers - alkene molecules), single covalent bond - so strong - scientists draw polymers with a repeating unit
• Monomers

  Identical small molecules - has a double to double covalent bond
• Repeating unit


  Shows a single to single carbon covalent bond - the covalent bond on either side have to stick out of the bracket showing how the polymer extends out in both directions - the little n shows how the polymer contains a lot of repeating units joined together
• Properties of polymers

  Most are solid at room temp - due to the strong intermolecular forces of attraction- a lot of energy needed to break it - high melting and boiling point
• Atoms become stable by gaining a full outer shell