Bonding

Bonding

What is a chemical bond?
1. This is a force that holds atoms together
2. Involves outershell electrons
Ionic Bonding
1. Strong net electrostatic forces of attraction
  1. Holds oppositely charged ions together
2. Giant ionic lattice
  1. Maximises attractive force between oppositely charged ions
  2. Minimises repulsion between similarly charged ions
  3. Forces of lattice are exerted equally in all directions
    1. Holds ions tightly
  4. Form ionic crystals
  5. Types of lattice structure
    1. Use of electron density maps
      1. Evidence for existence of ions
      2. X-rays passed through ionic crystal
        Diffracted by electrons
        Shows arrangement of ions
    2. Cubic structure
      1. Body-centred
      2. Face-centred
      3. Coordination number
        No of anions surrounding a single cation in a stable crystal structure
3. Occurs between metal and non-metals
4. Dot and cross diagrams used to show electron transfer
5. Ionic radius
  1. Radius of an ion in an orbital
  2. Increases in size down group
    1. Greater no. of electrons
  3. Across a period
    1. Anions larger
      1. Extra layer of electrons
    2. No. protons increases
      1. Electrons held more tightly
        Ionic radius falls
  4. Isoelectronic ions
    1. Falls across series
      1. Cations smaller
        Remaining electrons more strongly attracted to positive nucleus
      2. Anions larger
        Additional negative charge : electrons bound less tightly
6. Physical Properties Evidence for ions
  1. High melting & boiling temperatures
  2. Quite hard
  3. Brittle
    1. Differ from metals
    2. No sea of electrons
    3. Force put ions in one layer near ions in other layer
      1. Resulting repulsive force would force 2 layers apart
        Substance shatters
  4. Conduct electricity when molten or aqueous solution
    1. Lattice attraction of ions is overcome
      1. Ions become mobile
  5. Electroysis
    1. Positive species
      1. Attracted to cathode
    2. Negative species
      1. Attracted to anode
Covalent Bonding
Octet Rule
1. Elements tend to react to form an outershell of 8 electrons
Isoelectronic
1. Same electron configuration

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