Atomic Structure & Bonding

• Ionic bonding is the transfer of electrons from one atom to another.
• Covalent bonds are formed when two atoms share pairs of electrons.
• Metallic bonding is the electrostatic attraction between positive metal ions and delocalised electrons.
• Ionic compounds are bonded together because of the oppositely charged ions that create an attractive electrostatic force.
• Covalent bonds are held together by the electrostatic attraction between the positive nuclei and the negative electrons being shared with other nuclei.
• A giant covalent structure is a 3D structure made up of many covalently bonded atoms
• Allotropes are different forms of the same element, in the same physical state
• Graphite, graphene, and diamond are allotropes of carbon, in solid state
• Diamond is a giant covalent structure in which each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral, 3D structure
• Diamond’s properties include:

  • high melting and boiling points. Diamond’s many covalent bonds are strong and substantial energy is needed to break them.
  • does not conduct electricity. Diamond has no delocalised electrons to move and carry the charge.
  • hardness. Diamond’s three-dimensional tetrahedral structure with strong covalent bonds makes it very hard.
• Graphite has a giant covalent structure in which:

  • each carbon atom forms 3 covalent bonds with other carbon atoms
  • the carbon atoms form layers of hexagonal rings
  • there are weak forces of electrostatic attraction (van der Waals forces) between the layers, therefore they can slide past each other
  • there is one delocalised electron for each atom
• Graphite’s properties include:

  • high melting and boiling points. Graphite’s many covalent bonds are strong and substantial energy is needed to break them.
  • good electrical conductivity. Each carbon atom has a delocalised electron. The delocalised electrons are free to move and carry charge.
  • softness. The weak forces between graphite’s layers allow them to slide.
• Graphite is used as a lubricant and in pencils.
• Diamond-tipped tools are used to cut through hard rock, metals and glass.
• Graphene is a single-atom thick layer of graphite with strong covalent bonds between each carbon atom. The atoms are arranged in hexagons.
• Graphene's properties include:

  • high melting and boiling points. Graphene’s many covalent bonds are strong and substantial energy is needed to break them.
  • good electrical conductivity. Each carbon atom has delocalised electron. The delocalised electrons that are free to move and carry charge.
  • very strong. Graphene’s strong covalent bonds makes it 100 times stronger than steel. It is also the thinnest material possible – one atom thick – and very lightweight and transparent.
• Metals are giant lattices of positive ions arranged in regular layers, with delocalised electrons free to move throughout the structure.
• Properties of metallic structures include:

  • high melting and boiling points. High temperatures are required to break strong metallic bonds.
  • good electrical conductivity. Metal’s delocalised electrons can move and carry charge.
  • malleable and ductile. Metal’s layers of ions can slide over each other, but are still held together by the delocalised electrons. This means metal is malleable (it can be hammered into shape) and ductile(it can be drawn out into wires).
• The properties of giant ionic lattice structures include: high melting and boiling points, soluble, conductive when in aqueous or molten state.
• The trends in the periodic table:

  • Group I elements react very quickly with water
  • reactivity of Group I increases as you go down the group
  • Melting point decreases going down Group I
  • Transition elements are denser than Group I elements 
  • Reactivity decreases going down Group VII 
  • Noble gases are unreactive