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Hybridisation of s and p orbitals in alkanes, alkenes and alkynes. Unit 3. 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.
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Hybridisation of s and p orbitals in alkanes, alkenes and alkynes Unit 3
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 1s2, 2s2, 2p2 1s2 2s2 2p2 Increasing energy
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.
sp3 hybridisation 2p2 2p3 4 x sp3 hybridised orbitals 2s2 2s1
Shape of sp3 hybridised orbitals 4 x sp3 hybridised orbitals
e.g. methane σ σ σ σ 4 sigma bonds formed due to end-on overlap between each sp3 hybrid orbital of carbon and the 1s orbital of hydrogen
sp2 hybridisation In alkenes, the C atom bonds to three other atoms. 2p2 1 x unhybridised p-orbital 2p3 2s2 2s1 3 x sp2 hybridised orbitals
Shape of sp2 hybridised orbitals 3 x sp2 hybridised orbitals
e.g. ethene 5 sigma bonds formed – 4 due to end-on overlap between two of the sp2 hybrid orbitals of each carbon and the 1s orbital of hydrogen and 1 due to end-on overlap of the remaining sp2 hybrid orbitals of each carbon. 1 pi bond formed when the unhybridised p-orbital of each carbon undergo side-on overlap.
sp hybridisation In alkynes, the C atom bonds to two other atoms. 2 x unhybridised p-orbitals 2p2 2p3 2s1 2 x sp hybridised orbitals 2s2
e.g. ethyne 3 sigma bonds formed – 2 due to end-on overlap between one of the sphybrid 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.