Each carbon in a diamond crystalis bonded to four other carbon •Fullerene -These are small molecules ofatoms making a giant carbon in which the giant structure ismacromolecular array (lattice). As closed over into spheres of atoms (buckyeach carbon has four single bonds balls) or tubes (sometimes caled nano-it is sp3 hybridised and has tubes).tetrahedral bond angles of 109º •The smallest fullerene has 60 carbon28 atoms arranged in pentagons and hexagons like a football. This is calledAgain the carbon atoms in graphite Buckminsterfullerene.are bonded together to make a •The bonding has delocalised pi moleculargiant structure but in this case all of orbitals extending throughout thethe carbons are bonded to only structure and the carbon atoms are athree neighbour and are mixture of sp2 and sp3 hybridisedsp2 hybridised. As the systems.sp2 hybridisation results in planar •They are non- conductors as thestructures, there are giant 2 individual molecules are only held to eachdimensional layers of carbon atoms other by weak van der Waals forces.and each layer is only weakly linkedto the next layer by Van der Waalsforces.
Each silicon atom is bridged to its neighboursby an oxygen atom.
Central atom: PP contributes: 5 e−5 x Cl contibute: 5 e−Total VSE: 10Total VSEP: 5Geometry: Trigonal Bipyramidal
Central atom: S S contributes: 6 e− 6 x F contibute: 6 e− Total VSE: 12 Total VSEP: 6 Geometry: OctahedralSF6•Each S–F bond makes four 90° and one 180° bond angles with the other bonds in the molecule.
Hybridisation• This model explains the tetrahedral geometry of carbon and other atoms.• The electron structure of carbon is 1s2 2s2 2p2 suggesting that it should only be able to form two bonds (using the two singly occupied orbitals). However it is known to make four single bonds in many compounds and indeed never forms just two bonds. This can be explained by hybridisation - the mixing of atomic orbitals producing degenerate orbitals used for bonding.
• sp3 hybridisation occurs when the 2s and 2p orbitals merge to become sp3 orbitals (all of equal energy, length etc.).• sp2 is the same except only two of the p orbitals are hybridised, leaving one p orbital unchanged• sp is the same except only one of the p orbitals is hybridised and two p orbitals are left unchanged
•Promote an electron from 2s to 2p to create an excited state... • with 4 unpaired electrons we can form 4 bonds • these bonds would be from 1 x C2s-H1s interaction and 3 x C2p-H1s interactions • but these bonds will have different lengths and strengths • the 3 C-H bonds from the p orbitals maybe expected to have H-C-H bond angles of 90 degrees•"Blend" (i.e. hybridise) the s and the threep orbitals... • since we "mixed" 4 orbitals, we get a set of 4 sp3 orbitals • each sp3 hybrid contains a single unpaired electron
The sp3 hybrid orbital looks like a "distorted" p orbital withunequal lobes.The 4 sp3 hybrids point towards the corners of atetrahedron.
Summary• sp3occurs when a C has 4 attached groups• sp3 has 25% s and 75% p character• the 4 sp3 hybrids point towards the corners of a tetrahedron at 109.5o to each other• each sp3hybrid is involved in a σ bond
• The bond formed by this end-to-end overlap is called a sigma bond. The bonds between the carbons and hydrogens are also sigma bonds.• In any sigma bond, the most likely place to find the pair of electrons is on a line between the two nuclei.
Sigma (σ) bond Pi (π) bondFormed due to the axial overlap of two orbitals (‘s- Formed by the lateral (sideways) overlap of two ‘p’s’, ‘s-p’or’p-p’). orbitals. There can be more than one pi bonds between theOnly one sigma bond exists between two atoms. two atoms.The electron density is maximum and cylindrically The electron density is high along the direction atsymmetrical about the bond axis. right angles to the bond axis.Free rotation about the sigma bond is possible. Free rotation about the pi bond is not possible.This bond can be independently formed, i.e., The pi bond is formed after the sigma bond haswithout the formation of a pi bond. been formed,Sigma bond is relatively strong. Pi bond is a weak bond.