Bonding

Bonding

1. What is a chemical bond?

   • This is a force that holds atoms together
   • Involves outershell electrons

2. Ionic Bonding

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

3. Covalent Bonding

4. Octet Rule

   • Elements tend to react to form an outershell of 8 electrons

5. Isoelectronic

   • Same electron configuration

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