Bonding and structure

• Bonding is important in chemistry, as that's the process where molecules and compounds form
• Ionic bonding


  Takes place in compounds made from metals and non-metals so that the outer shells are completed in the atoms
• Metals in ionic bonding


  Lose electrons to become positively charged ions
• Non-metals in ionic bonding

  Gain electrons to become negatively charged ions
• Ionic compounds are formed in giant lattices built of lots of ions where the forces act in all directions of the lattice
• Space filling model


  Represents the relative size of ions and how they are arranged in one layer of the lattice
• 3D space filling model


  Represents how all the layers of the ionic lattice fit together
• Ball and stick model


  Represents ions as balls and bonds as sticks to show the 3D structure
• Ionic bonding diagram


  Dot and cross diagram that shows how electrons are transferred from the outer shell of a metal to the outer shell of a non-metal
• Dot and cross diagrams can also be used to show how electrons are shared between non-metals in covalent bonding molecules
• Covalent bonding


  Atoms share a pair of electrons to complete their outer shells
• Covalently bonded substances


  • May consist of small molecules with low melting and boiling points because the intermolecular forces between molecules are weak
  • As the molecules get larger, their melting and boiling points increase
  • Do not conduct electricity
• Giant covalent structures


  Very large structures where molecules are linked by covalent bonds
• Giant covalent structures


  • They have high melting and boiling points due to the strength of the covalent bonds
  • Most do not conduct electricity as there are no freely moving charged particles
• Giant covalent structures


  • Graphite
  • Diamond
  • Silicon dioxide (silica)
• In a diamond, each carbon atom is bonded to four others in a very rigid lattice - a tetrahedral arrangement
• Why diamond has high melting point and hardness

  It has a giant covalent structure with strong bonds
• Metallic bonding


  Delocalised free-moving electrons allow metals to conduct electricity
• Metals consist of giant structures of tightly packed positive ions in regular patterns and delocalised electrons
• The negative electrons are free to move through the structure and give rise to strong metallic bonds
• Metals are good conductors of electricity and heat
• Most metals also have high melting and boiling points
• Pure metals tend to bend easily because of their structure of regular layers of same size ions
• Other metals are mixed to make alloys which are harder
• The covalent bonds in diamond are exceptionally strong, and so diamond is very hard and has a high melting point but it doesn't conduct electricity because it doesn't have any delocalised electrons or ions
• In graphite, each carbon atom is covalently bonded to three of its neighbours
• The spare electron in graphite is delocalised between the layers which means graphite conducts electricity
• Graphene is simply one layer of graphite
• Graphene


  • It is incredibly strong, transparent, and an excellent conductor of heat and electricity because it has delocalised electrons
• Fullerenes


  Hollow-shaped carbon structures based on hexagonal rings of carbon atoms joined by covalent bonds
• Buckminsterfullerene is a fullerene with sixty carbon atoms arranged in a football shape
• Diamonds - in diamond, each carbon atom forms four covalent bonds with other carbon atoms, so diamond is very hard
• Graphite - Each carbon atom forms three covalent bonds with three other carbon atoms, forming layers of hexagonal rings - one electron from each carbon atom is delocalised
• Graphene is a single layer of graphite and has properties that make it useful in electronics and composites
• Fullerenes are molecules of carbon atoms with hollow shapes
• The first fullerene to be discovered was Buckminsterfullerene shaped like a sphere