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Shapes of Molecules. Valence Shell Electron Pair Repulsion Theory (VSEPR) Electrons can be placed in two categories Bonding pairs [involved in a bond]

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Presentation on theme: "Shapes of Molecules. Valence Shell Electron Pair Repulsion Theory (VSEPR) Electrons can be placed in two categories Bonding pairs [involved in a bond]"— Presentation transcript:

1 Shapes of Molecules

2 Valence Shell Electron Pair Repulsion Theory (VSEPR) Electrons can be placed in two categories Bonding pairs [involved in a bond] Lone pairs [not involved in a bond]

3 HH H Lone Pair Bonding Pairs N NH 3 Ammonia N has Atomic Number 7 Electron pattern 2,5

4 Bonding pairs Involved in a bond usually one e - from each atom in the bond Dative bond is a special type of covalent bond where one atom supplies both the electrons. This is unusual. The electrons in bonding pairs have opposite spins this is why they can come together. Single, double and triple bonds are all regarded as just one bonding pair

5 Bonding Pairs 4 bonding pairs All repel equally Move as far apart as possible Note they are NOT on the equator but one at the pole and three below the equator HH H C H Bond Angle HCH =109.5 0 Methane CH 4 Tetrahedral

6 Lone Pairs These are pairs of electrons not involved in a bond. Lone pairs have a greater power of repulsion than bonding pairs. They push other electron pairs further away from themselves than bonding pairs do.

7 Repulsion Lone Pair Bonding PairLone Pair Bonding Pair

8 H H H N Ammonia NH 3 3 bonding : 1 lone

9 In each slide a three dimensional representation methane will be left in the top left hand corner for purposes of comparison

10 HH H N Lone Pair Repels more Methane Bond angle 109.5 0 Tetrahedral

11 HH H N Methane Bond angle 109.5 0 Tetrahedral Bond angle 107 0 Lone Pair Repels more Pyramidal Group V element at centre

12 BF 3 F F F B

13 B F F F

14 BCl 3 B F F F 3 bonding pairs

15 Bond Angle = 120 o Planar or Trigonal Planar Side View Group III element at centre Top View

16 C H H O 3 bonding 0 lone Trigonal Planar Bonding Pairs HCHO methanal

17 O H H H2OH2O

18 O H H H2OH2O

19 O H H H2OH2O

20 Water H 2 O Methane Bond angle 109.5 0 Tetrahedral O H H

21 Water H 2 O Methane Bond angle 109.5 0 Tetrahedral O H H 2 lone pairs push hard bond angle = 104.5 V shaped or Angular

22 BeCl 2 Be Cl Beryllium Atomic Number 4 Electron pattern 2,2

23 BeCl 2 Be Cl

24 BeCl 2 Be Cl

25 BeCl 2 Be Cl 2 bonding Pairs

26 BeCl 2 2 bonding Pairs Bond Angle = 180 o Linear Cl Be

27 2 bonding pairs O = C = OLinear Bond Angle 180 o C O O CO 2

28 Rules Select the central atom Find out how many bond pairs and lone pairs you have Using repulsion rules decide a shape for the molecule

29 What shapes are the following Molecules? CCl 4 CHCl 3 CO 2 SiCl 4 CF 4 H 2 O BeH 2 H 2 S AlH 3 HCHO BF 3 BCl 3 H 3 O + PH 3 NH 3 SO 2

30 Examples of Molecular Shapes CCl 4 CHCl 3 SiCl 4 CF 4 NH 4 + BeH 2 CO 2 [C 2 H 2 ] H 2 S H 2 O SO 2 Tetrahedral [5atoms] Linear [ 3 atoms]Angular [3 atoms] Pyramidal [4 atoms] AlH 3 HCHO BF 3 BCl 3 H 3 O + PH 3 NH 3 Trigonal [4 atoms] Have 1 lone pair Have 2 lone pairs

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