1. Reactions of Alkenes Z E Z 1.7.3
understand that they are unsaturated hydrocarbons with a carbon-carbon double bond which consists of a  and a  bond
describe the addition reactions of alkenes
Independent Learning (HW) – pp and ALL questions therein
Connector: Identify whether the compounds below are E or Z isomers
C=C
H3C H
CH3 Z E Z
Crowe2008

2. The structure of methane
In methane all the C-H bonds are the same and due to mutual repulsion they are arranged in a tetrahedral structure – How can we explain this?

3. Electronic configuration and orbital theory
Carbon At. No. 6
Electron arrangement (GCSE) 2.4
Electronic configuration of carbon is 1s22s22p2
Orbitals are a way of showing the probability of finding an electron in a certain position:
s orbitals are spherical and p orbitals are dumbbell shaped

4. Shapes of orbitals Spherical s orbitals are centred on the nucleus
Dumbbell shaped p orbitals are also centred on the nucleus, but are arranged at right angle to each other.

5. The order of filling orbitals
2s orbital has a slightly lower energy than the 2p orbitals, so fills first.
The energies of the various orbitals in the first and second levels.
Electrons fill low energy orbitals (closer to the nucleus) before they fill higher energy ones.

6. Bonding in Carbon How many unpaired electrons?
In this arrangement carbon would form two bonds.
For carbon to form four bonds all four electrons must be unpaired, so one of the 2s electrons is promoted to the vacant 2pZ orbital

7. Bonding in methane
Remember - in methane all the C-H bonds are the same
In this arrangement the electrons are not in the same environment.
To account for the observation that all bonds are equal - The electrons rearrange themselves again in a process called hybridisation. This reorganises the electrons into four identical hybrid orbitals called sp3 hybrids (because they are made from one s orbital and three p orbitals).

8. Bonding in methane sp3 hybrid orbitals
All equal, arranged in a tetrahedral shape
Bonds formed in this way are called sigma (σ) bonds

9. The nature the C=C bond Ethene is a planar, 2D structure
With bond angles of approximately 120o
Once again the 2s orbitals are hybridised, but in this case sp2 hybrid orbitals form
The sp2 hybrid orbitals are shown in green – they are in the same plane and roughly 120o apart
The p orbital contains an unbonded electron

10. The bonding in ethene
The two carbon atoms and four hydrogen atoms would look like this before they joined together:
The various atomic orbitals which were pointing towards each other now merge to give molecular orbitals, each containing a bonding pair of electrons. These are sigma bonds (σ)

11. The pi (π) bond
The p orbitals shown in red overlap to produce a different type of molecular orbital - a pi (π) bond, that lies above and below the C-C σ bond
A pi bond is a region of space in which you can find the two electrons which make up the bond. Those two electrons can live anywhere within that space.
Note: The presence of the π bond makes the C=C bond rigid

12. Addition reactions of alkenes
Chemical compounds of the type X—Y will add across the double bond of an alkene.
X Y
X Y
H2C CH2
H2C CH2
Br Br
Br Br
H2C CH2
dibromoethane
H OH
H OH
H2C CH2
ethanol

13. Write equations and name the products formed when ethene reacts with the following reagents:
the addition of hydrogen with a nickel catalyst to form an alkane
the addition of halogens to produce di-substituted halogenoalkanes (Cl2 & Br2)
the addition of hydrogen halides to produce mono-substituted halogenoalkanes (HCl & HBr)

14. Oxidation of the double bond by potassium manganate (VII) to produce a diol
Write the corresponding reaction for cyclohexene, and name the product