Carbon functional groups and isomerism

• Water molecule


  Two hydrogen atoms form single polar covalent bonds with an oxygen atom
• Water molecule

  • Oxygen is more electronegative than hydrogen, so the region around oxygen has a partial negative charge and the region near the two hydrogen atoms has a partial positive charge
  • Each bond is directed towards one corner of a tetrahedron (perfect tetrahedral angle of 109.5°)
  • Lone pairs (LP) repel each other more than bonding pairs, reducing bond angle to 104.5°
• Moles

  • 1 mole of a compound always contains 6.02 x 10^23 molecules (Avogadro's number)
  • 1 mole of a substance is equivalent to its molecular mass in grams
• Concentration

  A 1 molar (1M) solution of a substance contains 1 mole/litre (1 mole/dm^3) of solution
• Water dissociation

  • Protons transferred between water molecules
  • Hydronium ion H3O+
  • Hydroxide ion OH-
• Kw

  • Water dissociation constant = [H+][OH-] = 10^-14 (at a set temperature and pressure)
  • In pure water [H+] = 10^-7 M; [OH-]=10^-7 M
• pH

  • pH = -log10[H+]
• A solution of pH 3 has [H+] of 10^3 M and [OH-] of 10^-11 M, and is twice as acidic as a solution of pH 6 and a thousand times as acidic as a solution of pH 6
• Effects of hydrogen bonds in water

  • higher boiling point
  • higher cohesion
  • high heat of vaporisation
  • ice has a more open structure than liquid water so floats
  • higher surface tension
  • higher specific heat
  • water is a good solvent for polar molecule
  • water is a good solvent for ionic compounds (forming hydration shells)
  • the oil drop effect
• Number of hydrogen bonds in ice v water

  ice = 4

  water = 3.7
• define heat of vaporisation:

  energy to convert 1g of water from liquid to gas at 25 degrees
• Define specific heat capacity:

  amount of heat absorbed or lost in order to alter the temperature of 1g of water by 1 degree
• heating up breaks hydrogen bonds

  cooling down forms hydrogen bonds
• what is the oil drop effect:

  water molecules next to the non-polar (hydrophobic) molecules cannot satisfy their hydrogen bonding requirements so are less stable

  So to maximise the number of hydrogen bonds which can be formed, clustering od non-polar molecules
• $kw=$${[H+][OH-]}/{[H2O]}$