VSEPR (Valence shell electron pair repulsion theory)
- The idea that electron pairs repel each other and move as far as they can from each other in order to minimise repulsions
- Not all electron pairs are shared during bonding- these are known as lone pairs
- The pairs of electrons that are shared/involved in bonding are called bonding pairs
- If a molecule consist of bonding pairs and no lone pairs the molecule is symmetrical
- If lone pairs are present, symmetrical shape is distorted
Drawing 3D Molecules
- Seen to be on plane of paper
- Seen to be going into paper away from you
- Seen to be coming out of paper towards you
This is very important in AS/A-level Chemistry, it may be difficult to imagine in your head, try building models to get a better concept!👨🏫
Linear shape
- A Molecule that consists of a central atom surrounded by two atoms
- bond angle of 180 degrees
It arranges itself in a linear shape so the electron pairs within the bonds are as far away as possible.
Double bonds do not effect the shape. E.g. Carbon dioxide consists of a carbon atom surrounded by two oxygen atoms that have double bonds with the carbon atom, yet it is still a linear molecule.
Trigonal Planar
- A Molecule that consists of a central atom surrounded by three atoms
- bond angle of 120 degrees
- It arranges itself in a trigonal planer shape so the electron pairs within the bonds are as far away as possible.
Tetrahedral
- A Molecule that consists of a central atom surrounded by four atoms
- bond angle of 109.5 degrees
- It arranges itself in a trigonal planer shape so the electron pairs within the bonds are as far away as possible.
Trigonal bipyramid
- A Molecule that consists of a central atom surrounded by five atoms
- bond angle of 90 and 120 degrees
- It arranges itself in a trigonal bipyramid shape so the electron pairs within the bonds are as far away as possible
Octahedral
- A Molecule that consists of a central atom surrounded by six atoms
- bond angle of 90 degrees degrees
•It arranges itself in a octahedron shape so the electron pairs within the bonds are as far away as possible.
Make sure you know all the names of the shapes as they will appear in AS/A-level chemistry exams! 👨🏫
Reference:
https://getrevising.co.uk/resources/molecular-shapes
This is the end of the topic!
Drafted by Cherry (Chemistry)