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• Covalent bonding


  Strong and the molecules are slightly polar
• This means the molecules have a separation of charge
• Ionic bonding


  The atoms involved in the reaction donate or receive electrons
• The atom, or part of the molecule, gains one or more electrons and becomes a negative ion (anion)
• The other atom, or part of the molecule, loses one or more electrons and becomes a positive ion (cation)
• Strong forces of attraction called ionic bonds hold the oppositely charged ions together
• Important inorganic ions in living organisms

  • Nitrate ions
  • Phosphate ions
  • Chloride ions
  • Sodium ions
  • Calcium ions
  • Hydrogen ions
  • Magnesium ions
• Inorganic ions play specialised roles in living organisms
• Covalent bonding


  The atoms involved in the reaction share electrons. Covalent bonds are very strong and the molecules formed are usually neutral. However, in some covalent compounds, the molecules are slightly polarised as the electrons in the covalent bonds are not quite evenly shared. This means the molecule has a part that is slightly negative and a part that is slightly positive. This separation of charge is called a dipole, and the tiny charges are represented as δ+ and δ-. The molecule is described as a polar molecule. This polarity is particularly common if one or more hydrogen atoms are involved in the bond.
• Formation of hydrogen molecules and water molecules


  • Examples of covalent bonding
• Inorganic ions


  When ionic substances are dissolved in water, the ions separate. Cells are 60-70% water, and so in living organisms most ionic substances exist as positive and negative ions. Many of these ions play specialised roles in individual cells and in the functioning of entire organisms
• Important anions


  • Nitrate ions (NO3-)
  • Phosphate ions (PO4^3-)
  • Chloride ions (Cl-)
  • Hydrogen carbonate ions (HCO3-)
• Important cations


  • Sodium ions (Na+)
  • Calcium ions (Ca2+)
  • Hydrogen ions (H+)
  • Magnesium ions (Mg2+)
• Water


  The medium in which all the reactions take place in living cells. Without it substances could not move around the body. Water is one of the reactants in the process of photosynthesis, on which almost all life depends. And water is a major habitat-it supports more life than any other part of the planet.
• Water molecule


  • Two atoms of hydrogen joined to one atom of oxygen. The electrons are held closer to the oxygen atom than to the hydrogen atoms, making water a polar molecule.
• Hydrogen bonding


  The slightly negative oxygen atom of one water molecule will attract the slightly positive hydrogen atoms of other water molecules in a weak electrostatic attraction called a hydrogen bond. This means that the molecules of water 'stick together' more than you might otherwise expect, because although each individual hydrogen bond is weak, there are a great many of them.
• Properties of water


  • Water is a polar solvent, an excellent transport medium, reaches maximum density at 4°C, slow to absorb and release heat, cannot be compressed, cohesive, and adhesive.
• Ionic bond


  Attractive forces between oppositely charged ions
• Covalent bond


  Formed when atoms share electrons
• Ionic substance


  Substances that dissociate into positive and negative ions when dissolved in water
• Polar substance


  Substances with a separation of charge, where part of the molecule is slightly negative and part is slightly positive
• Dipole


  The separation of charge in a molecule when the electrons in covalent bonds are not evenly shared
• Polar molecule


  A molecule containing a dipole
• Hydrogen bond


  Weak electrostatic intermolecular bonds formed between polar molecules containing at least one hydrogen atom
• Covalent bonding


  The atoms involved in the reaction share electrons
• Covalent bonds


  • Very strong
  • Molecules formed are usually neutral
  • In some covalent compounds, the molecules are slightly polarised
• Polarity


  The separation of charge in a molecule when the electrons in covalent bonds are not evenly shared
• Polarity


  • Represented as δ+ and δ-
• Polar molecule


  A molecule containing a dipole
• Polarity is particularly common if one or more hydrogen atoms are involved in the bond
• Formation of hydrogen molecules and water molecules

  Covalent bonding
• Important anions


  • Nitrate ions (NO3-)
  • Phosphate ions (PO4-)
  • Chloride ions (Cl-)
  • Hydrogen carbonate ions (HCO3-)
• Important cations


  • Sodium ions (Na+)
  • Calcium ions (Ca2+)
  • Hydrogen ions (H+)
  • Magnesium ions (Mg2+)
• Water


  The medium in which all the reactions take place in living cells
• Water


  • It is one of the reactants in the process of photosynthesis
  • It is a major habitat that supports more life than any other part of the planet
• Water molecule


  Two atoms of hydrogen joined to one atom of oxygen
• Polarity of water molecule

  Electrons are held closer to the oxygen atom than to the hydrogen atoms
• Hydrogen bonds


  Weak electrostatic attraction between the slightly negative oxygen atom of one water molecule and the slightly positive hydrogen atoms of other water molecules
• Hydrogen bonds in water

  • They cause the water molecules to 'stick together' more than expected
  • They give water relatively high melting and boiling points compared to other substances with similar sized molecules
• Polar solvent


  Water can dissolve many ionic and polar covalently bonded substances