Describe and explain the type of bonding in ethane, ethene, and benzene. Compare their reactions with bromine.

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Describe and explain the type of bonding in ethane, ethene, and benzene. Compare their reactions with bromine.

Ethane:

The bonding in ethane is a covalent bond between carbon and hydrogen. This involves the sharing of two electrons. The two carbons in the molecule also form a single bond with each other, also a covalent bond. There is a diagram of the molecule below: Each of the bonds displayed here is a sigma bond. The bonds hold the carbon ions together by an electrostatic attraction.

Ethene:

The bonding in ethene is similar to that in ethane; however between the two carbon atoms there is a double bond, one sigma bond and one Pi bond. The pi bond is formed by two p-orbital electrons overlapping to create a bond above and below the sigma bond. This creates an electron dense area in between the two carbons and makes the molecule less stable, as it is now prone to electrophiles, species that are attracted to the electrons in the pi bond. The two electrons in the pi bond are not always near to the nucleus of the carbon atoms, therefore they do not attract the two atoms as closely, and so the pi bond is weaker than the sigma bond. However the pi and sigma bonds together are stronger than the single sigma bond in ethane and so the C=C bond is shorter and stronger than the C-C bond. As the sigma bond is symmetrical about the axis of the two carbon atoms the carbon atoms are free to rotate about the bond. However, in ethene the pi bond is not symmetrical and therefore the carbon molecules are not free to rotate, this means that for any products of ethene with the double bond remaining intact there is cis-trans isomerism. There is a diagram below, the green lines indicate the pi bonds, and the black lines indicate the sigma bonds.

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Benzene:

The benzene ring is a very different molecule to these previous two; firstly, it is a ring, with each carbon connected to another carbon. The bonding between the carbons and hydrogens is normal; there is a shared pair of electrons which forms a covalent sigma bond. However, the bonding between the carbon atoms is strange. There is not a single bond, nor a double bond, but a ring of delocalised electrons free to move inside the ring. The delocalised ring is located above and below a sigma bond, just as in ethene, but here the electrons ...

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