Bonding

• Ionic bonding


  1. Metal atom loses electrons and becomes a cation (+)

  2. Non-metal gains electrons and becomes an anion (-)

  3. Strong electrostatic forces of attraction between oppositely charged ions
• Dot and cross diagrams

  Show how ionic bonds form
• Covalent bonding


  1. Non-metals bond together, each atom gives one electron to form a bond pair with opposed electron spins

  2. Electrostatic attraction between positive nuclei and shared electrons
• Dot and cross diagrams

  Show how covalent bonds form
• Single bonds


  • Water (H2O)
• Double bonds


  • Oxygen (O2)
• Coordinate bonding


  Same as a covalent bond but both electrons forming the bond pair come from the same atom
• Very few compounds are purely ionic or purely covalent, many have bonds that are intermediate between pure covalent and pure ionic</b>
• Polar bonds


  Bonds that are intermediate in character between pure covalent and pure ionic, degree depends on difference in electronegativity
• The greater the difference in electronegativity, the greater the ionic character
• Electronegativity


  Measure of how strongly atoms attract electrons in a covalent bond, higher value means better element can attract bonding electrons
• Polar covalent bond


  Bonding electrons are pulled towards the more electronegative atom, which takes up a slightly negative charge
• Non-polar covalent bond


  Atoms have equal electronegativities, electrons are equally shared
• Electronegativity difference ranges


  • Less than 0.4 - non-polar covalent
  • 0.4 to 1.9 - polar covalent
  • 2.0 or more - ionic
• Dipole-dipole forces


  Attraction between slightly positive and slightly negative regions of polar molecules
• Induced dipole-induced dipole forces

  Attraction between temporary dipoles induced in non-polar molecules
• Van der Waals forces

  Dipole-dipole and induced dipole-induced dipole forces
• Hydrogen bonds


  Special intermolecular forces between hydrogen atoms bonded to small highly electronegative elements with lone pairs
• Hydrogen bonds


  • Increase boiling points
  • Increase solubility