AS Chemistry - Structure and Bonding.

Revision notes for the Structure and Bonding topic. 

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  • Created by: Lalizziee
  • Created on: 04-12-11 14:05

Ionic Bonding

Ions are formed by the transfer of electrons from the highest occupied energy levels from metal to non-metalic.

Cations - POSIVITE IONS, are fomed when atoms lose electrons. 

Anions -  NEGATIVE IONS, are formed when atoms gain electrons. 

The atoms in forming ions achieve the electron arrangement of the nearest noble gas.

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Ionic Bonding

There is a strong electrostatic attraction between the oppositely charged ions - this is what we call the IONIC BOND.

Ionic crystals have a giant ionic lattice structure....

(http://www.tf.uni-kiel.de/matwis/amat/def_en/kap_2/illustr/nacl_gitter.gif)

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Ionic Bonding

*Note* Ionic compounds do NOT exist as molecules.

Formulae for ionic compounds.

Group 7    Group 6    Group 5                               Group 3    Group 2    Group 1

  -1               -2               -3                                        +3             +2            +1

e.g. Potassium (Group 1) Sulphate (Group 6). {K+ & S2-}

         = K2S.

e.g. Caesium (Group 1) Oxide (Group 6). {Cs+ & O2-}

       = Cs2O

------------------------------------------------------------

Carbonate = CO3 2-                Sulphate = SO4 2-            Nitrate = NO3 -

Hydroxide = OH-         Hydrogen carbonate = HCO3 -   Ammonium = NH4 +

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Covalent Bonding

A covalent bond is the sharing of a pair of electrons between two atoms. 

It is formed by the overlap of the orbitals that contain unpaired electrons. 

e.g.

(http://www.bbc.co.uk/schools/gcsebitesize/science/images/diag_hyd_chloride.gif) <- Only outer electons are shown. 

The electron pair creates a bonf between the two atoms becasue it attracts the neucleus of each atom and so resists the seperation of the two atoms. 

When atoms combine & form covalent bonds MOLECULES are formed.

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Co-ordinate Bonding

A co-ordinate bond (also called dative covalent bond) is formed when one atom provides the pair of electrons for a covalent bond. 

Once fomed, co-ordinate bond is identical to a covalent bond. 

To form a co-ordinate bond one atom must have a lone pair of electons and another atom must have a vacant orbital. 

We use and arrow to reprosent a co-ordnate bond. It shows the movement of a pair of electrons. 

                                (http://upload.wikimedia.org/wikipedia/commons/thumb/e/e0/Coordinate_Covalent_Bonding.gif/220px-Coordinate_Covalent_Bonding.gif)

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Metallic Bonding.

                                (http://www.bbc.co.uk/schools/gcsebitesize/science/images/gcsechem_60.gif)

Metals consist of a lattice of positive ions surrounded by de-localised electrons. The metallic bond is the attraction between the de-localised electrons and the positive metal ions. Only the electrons in the highest occupied energy level become de-localised.

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Shapes of Molecules and bonding.

The shapes of simple molecules and ions and their bond angles can be predicted from the arrangement of their outer bonding electron pairs and the number of lone pairs. 

Electron pairs repel each other and arrange themselves to minimise repulsion by being as far apart as possible. 

It is the repulsion between  electron pairs which determines the shape, not the repulsion between the atoms.

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To be finished soon...

Sorry for any inconvenience

Cards will be finished at a later date.

Lizzy. x 

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