C2 - Bonding, Structure and Properties of Matter

• What is ionic bonding?

  When a non-metal and a metal react together, the metal atoms loses electrons to form a positively charged ion and the non-metal gains these electrons to form a negatively charged ion. These oppositely charges are strongly attracted by electrostatic forces.
• What structure do ionic compounds have?

  A giant ionic lattice - these ions form a closely packed regular lattice arrangement and there are very strong electrostatic forces of attractions between oppositely charged ions, acting in all directions of the lattice.
• Properties of ionic compounds:

  • High melting points
  • High boiling points
  • Can only conduct electricity when molten or dissolved in water so the ions are free to move
• What is covalent bonding?

  When non-metal atoms bond together, they share pairs of electrons to make covalent bonds. The positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces, making covalent bonds very strong.
• What are simple molecular substances?

  Substances made up of molecules containing a few atoms joined together by covalent bonds
• What makes simple molecular substances weak?

  The intermolecular forces of attraction between molecules are very weak, which requires little energy to break - this means the melting and boiling points are low
• What are polymers?

  Large molecules made up of repeating units called monomers - they are joined by strong covalent bonds
• Why are most polymers solid at room temperatures?

  The intermolecular forces between polymers are larger, so more energy is needed to break them. HOWEVER, the intermolecular forces are still weaker than ionic or covalent bonds so they generally have lower boiling points than ionic or giant molecular compounds.
• What are examples of giant covalent structures (3) ?

  Diamond

  Graphite

  Silicon dioxide
• Why is diamond very hard?

  It has a giant covalent structure, made up of carbon atoms that each form four covalent bonds - these require a lot of energy to break down.
• Describe the structure of Graphite?

  Each carbon atom forms 3 covalent bonds, creating sheets of carbon atoms arranged in hexagons

  No covalent bonds between layers - they're only held together weakly

  They're free to move over each other making graphite soft and slippery.

  Graphite has a high melting point - covalent bonds in layers need loads of energy to break

  Only 3 out of each carbon's four outer electrons are used in bonds so each carbon atom has one electron that's delocalised - graphite conducts electricity
• What are fullerenes?

  Molecules of carbon shaped like hollow balls - they can 'cage' other molecules which could be used to deliver a drug into the body. They also have a large surface area which makes a good catalyst.
• What are nanotubes?


  Fullerenes form nanotubes - tiny carbon cylinders.

  They can conduct both electricity and heat
• What is metallic bonding?

  Metallic bonding is the electrostatic attraction between positively charged metal ions and a sea of delocalised electrons. These forces of attraction hold atoms together in a regular structure.
• What are alloys?

  A mixture of two or more metals
• How are alloys harder than pure metals?

  Alloys have different sized atoms which will distort the layers, making it harder for the layers of atoms to slide over each other.