1. Hybridisation of s and p orbitals in alkanes, alkenes and alkynes Unit 3

2. The valency of carbon The valency of carbon Carbon has a valency of 4 i.e. it can form 4 bonds. However, the electronic configuration of a C atom is 1s 2, 2s 2, 2p 2 1s 2 2s 2 2p 2 Increasing energy

3. With this electronic configuration, carbon can only form 2 bonds as it only has two unpaired electrons. However, in alkanes carbon forms bonds with four other atoms. In oder for this to occur, one of the 2s electrons is promoted to the unfilled 2p orbital.

4. 2p 2 2s 2 4 x sp 3 hybridised orbitals sp 3 hybridisation 2p 3 2s 1

5. 4 x sp 3 hybridised orbitals Shape of sp 3 hybridised orbitals

6. e.g. methane σ σ σ σ 4 sigma bonds formed due to end-on overlap between each sp 3 hybrid orbital of carbon and the 1s orbital of hydrogen

7. 2p 2 2s 2 3 x sp 2 hybridised orbitals sp 2 hybridisation 1 x unhybridised p-orbital 2p 3 2s 1 In alkenes, the C atom bonds to three other atoms.

8. 3 x sp 2 hybridised orbitals Shape of sp 2 hybridised orbitals

9. e.g. ethene 5 sigma bonds formed – 4 due to end-on overlap between two of the sp 2 hybrid orbitals of each carbon and the 1s orbital of hydrogen and 1 due to end-on overlap of the remaining sp 2 hybrid orbitals of each carbon. 1 pi bond formed when the unhybridised p-orbital of each carbon undergo side-on overlap.

10. sp hybridisation In alkynes, the C atom bonds to two other atoms. 2s 2 2p 2 2s 1 2p 3 2 x sp hybridised orbitals 2 x unhybridised p-orbitals

11. Shape of sp hybridised orbital

12. e.g. ethyne 3 sigma bonds formed – 2 due to end-on overlap between one of the sp hybrid orbitals of each carbon and the 1s orbital of hydrogen and 1 due to end-on overlap of the remaining sp hybrid orbital of each carbon. 2 pi bonds formed when the two unhybridised p-orbitals of each carbon undergo side-on overlap.