2. Bonding  Compounds are formed when atoms join together.  They are held together by bonds.  Non – metal elements are joined together by a Covalent Bond.  A MOLECULE is a group of atoms held together by a covalent bond – e.g. carbon dioxide – CO 2 is a molecule – it is made of 1C atom joined to 2 O atoms.

3. Diatomic Molecules  These are made when 2 atoms join together.  They can be compounds – e.g. HCl, HBr. or  They can be elements – There are 7 diatomic elements:  Chlorine – Cl 2, Bromine- Br 2, Hydrogen -H 2, Flourine – F 2, Nitrogen – N 2, Oxygen – O 2, Iodine – I 2.

4. Chemical Formula  Steps:  Symbol for Element  Valency at Top  Cross Over Valency  Example – Carbon chloride  C Cl  C iv Cl  C 1 Cl 4

5. Full Structural Formula  This shows the way the atoms are arranged in a molecule.  Example – Methane CH 4 H I H - C - H I H

6. Electron Clouds  Electrons are arranged in energy levels.  Inside the energy level they are found inside electron clouds.  Each electron cloud can hold a maximum of 2 electrons.  Therefore: The 1 st energy level has one cloud.  The 2 nd and 3 rd energy levels hold 8 electrons inside 4 clouds.

7. Stability  When an atom has a full outer energy level – i.e. all the clouds in that energy level are full – the atom is stable. Examples – Noble gases.  When an atom does not have a full outer energy level, the atom will under go reactions, ( try to join with) with another atom, to achieve a full outer energy level.

8. Covalent bond  This is the type of bond that holds non metal atoms together.  The electrons in the half filled electron clouds, in the outer energy level, overlap with the clouds of another atom.  Both atoms share electrons and they both end up with a full outer energy level.

9. What holds the Atoms together?  Both the positive nuclei, of the joined atoms, are attracted to the negatively charged - shared electron clouds.  This force of attraction between positive and negative is called an Electrostatic attraction.  A covalent bond is a strong bond.

10. Shapes of Molecules  There some basis shapes to molecules:  Linear : Example - HCl  Bent or Planar : Example Water - H2OH2O  Pyramidal : Example Ammonia - NH 3  Tetrahedral: Example – Methane - CH 4