03/11/2014 Covalent structures

                                  Covalent structures

During this class, we learnt about lewis structures, the octet rule and the use of VSEPR.

 Lewis structures show all the valence electrons in a covalently bonded species, it shows all the domains in the valence shell that are used to predict molecular shapes.

Basic Lewis structure

Dr Carmichael approved Lewis structure

The 'Octet rule' refers to the tendency of atoms to gain a valence shell with a total of 8 electrons, exceptions being BeCl2, BF3 and SO3.  Atoms like these can form stable compounds without complete octets of electrons.

Molecular Shapes: 

Being able to work out the shape of a molecule allows us to find the physical properties of it. This is where the VSEPR comes to play, VSEPR is the Valence Shell Electron Repulsion Theory and it involves the use of domains. Lewis structures help us see these domains. 

For example: 

Draw and name the shapes of this molecule and write the bond angle. 

1) BF3

There are 3 domains in this structure therefore there are 3 numbers of electron pairs

 2) H20

H2O is a very interesting one because although it has 4 domains but only 2 are evident therefore it is v shaped. 

We then used the Ipads to further practise drawing the molecules.

The homework was page 3 on the "molecular shapes (2,3,4)" packet. 

Have fun :)

Sources: 

Mr Carmichael's presentation

The others drawn by Gedo