Bonding, Structure and Properties

• Compound

  A substance in which 2 or more elements are chemically combined
• Types of chemical bonds

  • Ionic
  • Metallic
  • Covalent
• Ionic compounds

  • Strong electrostatic attraction between oppositely charged ions means ionic compounds have high melting and boiling points
  • In a solid state, ionic compounds do not conduct electricity as the ions are fixed in place
  • When molten/ dissolved, ions can move around so then ionic compounds conduct electricity
  • They are brittle
• Metallic compounds

  • The layers of ions in metals are able to slide over each other, so metals are malleable and ductile
  • The delocalised electrons can move through the metal and carry charge, so metals conduct electricity and heat
  • Metallic bonds are very strong and require large amounts of energy to be broken, giving most metals high melting and boiling points
• Simple molecular covalent substances

  • Simple molecules have weak intermolecular forces between the molecules, so they have low melting and boiling points
  • Do not conduct electricity because simple molecules do not have an overall charge
  • They are usually gases or liquids
• Giant covalent substances


  • Substances with a giant covalent structure are solids with very high melting points
• Metallic bonding

  1. The electrons in the outer shell of metal atoms are delocalised and so they are free to move through the whole structure - 'sea' of delocalised electrons

  2. Metallic bonds form due to the electrostatic attraction between the positively charged metal ions and the negatively charged delocalised electrons
• Ionic bonding

  1. Electrons in the outer shell of the metal are transferred

  2. Metal atoms lose electrons to become positively charged ions

  3. Non-metal atoms gain electrons to become negatively charged ions

  4. The electrostatic attraction from these oppositely charged ions forms a giant ionic lattice

  5. The electron transfer can be represented by a dot and cross diagram
• Covalent bonding

  1. When atoms share pairs of electrons, they form covalent bonds

  2. The bonds between these atoms are strong

  3. Dot and cross diagrams can be drawn to represent the sharing of electrons
• Simple molecular substances have low melting and boiling points


  • Weak intermolecular forces between molecules - these are broken in melting or boiling, not the strong covalent bonds
  • The intermolecular forces increase with the size of the molecules, larger molecules have higher melting and boiling points
• Diamond

  • It is very hard, has a very high melting point and does not conduct electricity
  • Each carbon is joined to 4 other carbons covalently - covalent bonds need a lot of energy to be broken = very high melting point
  • This is the maximum number of bonds each carbon atom can make
• Graphite

  • Each carbon is covalently bonded to 3 other carbons, forming layers of hexagonal rings which have no covalent bonds between the layers
  • The layers can slide over each other due to the absence of covalent bonds between the layers, but there are weak intermolecular forces between layers - so graphite is soft and slippery
  • One electron from each carbon atom is delocalised so it can conduct electricity
• Graphene

  • Its structure resembles a single layer of graphite
  • Graphene has a very high melting point due to the very strong covalent bonds between the carbon atoms that require large amounts of energy to be broken
  • Conducts electricity due to the delocalised electrons that are free to move through its structure
• Fullerenes

  • Molecules of carbon atoms with hollow shapes
  • They are based on hexagonal rings of carbon atoms, but they may also contain rings with five or seven carbon atoms
• Carbon nanotubes

  • Cylindrical fullerenes with very high length to diameter ratios
  • They have very high tensile strength and conduct electricity due to the delocalised electrons present
• Individual atoms do not have the same properties as bulk materials
• Nanoparticles

  • 1-100 nanometers across
  • Contain a few hundred atoms
  • They have different properties from the 'bulk' properties which they form because of their high surface area to volume ratio
• Uses of nanoparticles

  • Nano-silver - kills bacteria: used in wound dressings, deodorants, or to line socks and fridges to kill bacteria causing bad smell
  • Nano-titanium dioxide - used in sunblock creams to block harmful UV rays without appearing white on the skin as the particles do not reflect visible light, also used in self-cleaning windows as they help break down dirt
• Risks of nanoparticles:

  • So small that they could potentially enter our blood stream.
  • Relatively new material so long term effects are unknown
  • Can enter and potentially damage the environment
• Thermochromic materials

  • Change colour when they reach a certain temperature
  • Used in mugs and spoons which change colour when their contents are hot
• Photochromic pigments

  • These pigments change colour when exposed to light
  • Used in sunglasses which darken in bright sun
• Polymer gels

  • Hydrogels absorb up to 1,000 times their volume in water
  • Certain stimuli (changes in pH and temperature) can cause the water to be released
  • Used in nappies, fake snow and hair gel
• Shape memory alloys/polymers

  • These materials can be bent and deformed but will return to their original shape when heated
  • Shape memory polymers are used in medical stitches and sports equipments such as gum shields
  • Shape memory alloys are used in car bodies and plates for bone fractures