Shapes of molecules & ions. VSEPR theory VSEPR - the Valence Shell Electron Pair Repulsion theory is used to obtain the shape of simple molecules and.

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Presentation transcript:

Shapes of molecules & ions

VSEPR theory VSEPR - the Valence Shell Electron Pair Repulsion theory is used to obtain the shape of simple molecules and ions

VSEPR theory VSEPR - the Valence Shell Electron Pair Repulsion theory is used to obtain the shape of simple molecules and ions It states that because of the repulsion between pairs of electrons around the central atom in the molecule or ion, the pairs of electrons are arranged to be as far away from each other as possible

Negative Charge Centres For VSEPR, multiple bonds (double, triple) count as if they are just one pair of electrons

Negative Charge Centres For VSEPR, multiple bonds (double, triple) count as if they are just one pair of electrons So VSEPR uses repulsion between negative charge centres rather than between pairs of electrons

4 bonding pairs - tetrahedral Bond Angle = 109.5º E.g methane - CH 4, CCl 4, SiCl 4 4 negative charge centres From:

3 bonding pairs (& 1 non-bonding pair) trigonal pyramid Bond Angle = 107 º E.g. ammonia - NH 3, PCl 3 4 negative charge centres From:

The bond angle decreases because the non-bonding pair of electrons exerts a greater repulsion than the bonding pair(s) From:

2 bonding pairs ( 2 non-bonding pairs) bent or v-shaped Bond angle = 105 º E.g. H 2 O, H 2 S 4 negative charge centres From:

2 negative charge centres Shape is always linear Bond angle is 180º E.g. From:

3 negative charge centres 3 bonding electron pairs, no non-bonding pairs Trigonal planar Bond angle is 120° e.g. BF 3, ethene, CO bonding pairs, 1 non-bonding pair Bent or v-shaped Bond angle is 120° E.g. SO 2, ozone - O 3 From:

5 and 6 charge centres Elements in the third period can have more than 8 electrons in their outer shell because the 3 d orbitals are close in energy to the 3p orbitals. The VSEPR theory also applies You do not have to know specific bond angles

5 negative charge centres (HL) Trigonal bipyramidal e.g. PCl 5 From:

5 negative charge centres (HL) 4 bonding pairs and 1 non-bonding pair Distorted tetrahedral From:

6 negative charge centres (HL) Octahedral e.g. SF 6 From:

6 negative charge centres (HL) 4 bonding pairs and 2 non-bonding pairs as far apart as possible (above & below plane) Square planar e.g. XeF 4 From:

VESPRtheory All the previous molecular shapes are based on VSEPR theory VSEPR=Valence Shell Electron Pair Repulsion theory Pairs of electrons arrange themselves around the central atom so that they are as far apart from each other as possible