3. Each carbon in a diamond crystal
is bonded to four other carbon •Fullerene -These are small molecules of
atoms making a giant carbon in which the giant structure is
macromolecular array (lattice). As closed over into spheres of atoms (bucky
each 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 carbon
28'
atoms arranged in pentagons and
hexagons like a football. This is called
Again the carbon atoms in graphite Buckminsterfullerene.
are bonded together to make a •The bonding has delocalised pi molecular
giant structure but in this case all of orbitals extending throughout the
the carbons are bonded to only structure and the carbon atoms are a
three neighbour and are mixture of sp2 and sp3 hybridised
sp2 hybridised. As the systems.
sp2 hybridisation results in planar •They are non- conductors as the
structures, there are giant 2 individual molecules are only held to each
dimensional layers of carbon atoms other by weak van der Waal's forces.
and each layer is only weakly linked
to the next layer by Van der Waal's
forces.

4. Each silicon atom is bridged to its neighbours
by an oxygen atom.

7. Central atom: P
P contributes: 5 e−
5 x Cl contibute: 5 e−
Total VSE: 10
Total VSEP: 5
Geometry: Trigonal Bipyramidal

16. Central atom: S
S contributes: 6 e−
6 x F contibute: 6 e−
Total VSE: 12
Total VSEP: 6
Geometry: Octahedral
SF6
•Each S–F bond makes four 90° and one 180° bond angles with the other bonds in the molecule.

19. 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.

20. • 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

21. sp3 hybridisation

22. •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 three
p orbitals...
• since we "mixed" 4 orbitals, we
get a set of 4 sp3 orbitals
• each sp3 hybrid contains a single
unpaired electron

23. The sp3 hybrid orbital looks like a "distorted" p orbital with
unequal lobes.The 4 sp3 hybrids point towards the corners of a
tetrahedron.

24. • http://www.chem.ucalgary.ca/courses/350/Carey

25. 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

26. • 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.

27. http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/bo

29. Sigma (σ) bond Pi (π) bond
Formed 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 the
Only one sigma bond exists between two atoms.
two atoms.
The electron density is maximum and cylindrically The electron density is high along the direction at
symmetrical 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 has
without the formation of a pi bond. been formed,
Sigma bond is relatively strong. Pi bond is a weak bond.