Structure and Bonding

• The three types of bonding are: ionic, metallic and covalent.
• Ionic bonds:

  • Non metal + Metal
  • Giant structure
  • High MP + BP
  • Can conduct

  eg. sodium chloride
• Metallic bonds:

  • Metal + Metal
  • Giant structure
  • High MP + BP
  • Can conduct

  eg. gold
• Covalent bonds:

  • Non metal + Non metal
  • Giant structure/Simple molecular
  • High MP + BP/Low MP + BP
  • Can't conduct

  eg. diamond/water
• Formation of ionic bonds:

  During ionic bonding, atoms take part in chemical reactions to achieve a FULL OUTER SHELL of electrons. They can do this by SHARING electrons with another atom, either LOSING or GAINING electrons. A transfer of electron(s) from the metal atom to the non-metal atom will occur. This will leave both atom with a CHARGE (protons and electrons not equal).
• POSITIVE IONS:

  Atoms with 1, 2 or 3 electrons in their outer shell (non-metal) must LOSE these electrons to achieve a FULL OUTER SHELL. It will now have fewer ELECTRONS than PROTONS, resulting in a positive charge. This is called a CATION.
• NEGATIVE IONS:

  Atoms with 5, 6 or 7 electrons in their outer shell (non-metal) must GAIN electrons to achieve a FULL OUTER SHELL. It will now have more ELECTRONS than PROTONS, resulting in a negative charge. This is called a ANION.
• IONIC COMPOUNDS:

  The electrostatic force of attraction between the positive metal ion and negative non-metal ion.
• CHARGES OF IONS:

  • Metal ions (Groups 1, 2 and 3) -> Charge = Group (+)
  • Non-metal ions (Groups 1, 2 and 3) -> Charge = 8 - Group (-)
  • Transition metals -> Charge = Roman numeral given (+)
• Ions to memorise (positive):

  • H^1+ (Hydrogen)
  • Ag^1+ (Silver)
  • Cu^2+ (Copper)
  • Fe^2+/Fe^3+ (Iron)
  • Pb^2+ (Lead)
  • Zn^2+ (Zinc)
  • NH.4^1+ (Ammonium)
• Ions to memorise (negative):

  • OH^1- (Hydroxide)
  • CO.3^2- (Carbonate)
  • NO.3^1- (Nitrate)
  • SO.4^2- (Sulfate)
• Ionic formulae are the 'phrases' which describe the ratio between the elements in the ionic bond.
• How to write ionic formulae:

  Write the metal ion, then the non-metal ion.

  • Na Cl
  • Mg O
  • Al O

  Write the charge of each ion after the elements.

  • Na^1+ Cl^1-
  • Mg^2+ O^2-
  • Al^3+ O^2-

  Drop and cross the charges without the +/-. Any common factors are cancelled out, and 1s aren't needed.

  • Na.1 Cl.1 -> NaCl
  • Mg.2 O.2 -> MgO
  • Al.2 O.3

  When writing with the 'to be memorised' ions, do the same, whilst taking into account the already written formula.
• Rules for dot-cross diagrams (ionic):

  • Only outer shell, unless specified
  • Square brackets with ions lost/gained at the top
  • +1/-1 aren't written
  • If there are 2 or more of an element, write the number there are before the square brackets.
• All ionic bonds are arranged in structures called lattices. A lattice is a giant structure, with high MP and BP (due to many strong ionic bonds, requiring lots of energy to overcome).

  
• Ionic compounds don't conduct electricity when solid, but when molten (liquid/gas) or in an aqueous solution. This is due to their ability to move.
• Formation of metallic bonds:

  When metals bond with other metals, they form metallic bonds. A metal by itself has an incomplete shell of electrons. When it bonds, it loses these electrons to the sea of delocalised electrons and gains a positive charge.
• METALLIC COMPOUNDS:


  The electrostatic force of attraction between the positive ions and the negative sea of delocalised electrons.
• Properties of metallic compounds:

  • High MP + BP -> Giant structures mean there are many strong metallic bonds to break.
  • Can conduct electricity -> Delocalised electrons can carry charge through the structure as they move around freely.
  • Malleable and ductile -> Layers of ions can easily slide over each other.
• Formation of covalent bonds:

  When non-metals bond with other non-metals, they form covalent bonds. To achieve its most stable from, the atom must achieve a FULL OUTER SHELL of electrons. It achieves this by sharing one or more pairs of electrons with another.
• COVALENT COMPOUNDS:

  The electrostatic force of attraction between the two nuclei and the shared pair of electrons.
• Covalent compounds can be giant or simple molecular.
• Rules for dot-cross diagrams (covalent):

  • Only outer shell unless specified
  • Big circle to represent shells
  • Element name inside
  • Overlap for bonds
  • Adjacent elements should have one as dots, and one as crosses.
• Properties of simple molecular covalent bonds:

  • Low MP + BP -> Weak intermolecular forces require little energy to be overcome. Covalent bonds aren't broken. Usually gases/liquids at RT.
  • Increasing MP + BP with increasing molecular mass -> Heavier molecules have more electrons (as they have more protons), giving the atoms stronger intermolecular forces. These require more energy to overcome.
• Properties of giant covalent bonds:

  • High MP + BP -> Giant structures have many strong covalent bonds to break, requiring high energy levels. Usually solids at RT.
• DIAMOND (Giant):


  • High MP + BP -> Many strong covalent bonds to break.
  • Very hard -> Rigid structure of atoms with strong bonds (4 bonds per carbon atom)
  • Doesn't conduct electricity -> No delocalised electrons
• GRAPHITE (Giant):


  • High MP + BP -> Many strong covalent bonds to break.
  • Soft + Slippery -> Layers of atoms can slide over each other (3 bonds per carbon atom)
  • Does conduct electricity -> Delocalised electrons can move throughout the structure
• C.60 FULLERENE (Simple Molecular):


  • Low MP + BP -> Only weak intermolecular forces need to be broken.
  • Soft -> Molecules can slide over each other (3 bonds per carbon atom)
  • Doesn't conduct electricity -> Delocalised electrons can't move between molecules, only within.
• Covalent compound USUALLY don't conduct electricity.