Alkanes

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The Bonding in Alkanes

Each carbon atom in alkanes is joined to four other single covalent bonds called sigma bonds. The sigma bond is positened in direct line between the bonded atoms.

Sigma bond = Overlap of 2 orbitals, one from each bonding atom

(http://www.chem.ucla.edu/harding/IGOC/S/sigma_bond06.png)

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Variations in the boiling points of alkanes

C1-C4 = Gases at RTP

C5-C16 = Colourless Liquids

C17+ = Waxy, White Solids

eg CH4 - Methane is a Gas

eg C5H12 - Pentane is a Solid

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First Four Alkanes

Man Eating Polar Bear

Methane - CH4

Ethane - C2H6

Propane - C3H8

Butane - C4H10

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Reactivity of Alkanes

alkanes do not react with most common reagents because:

• C-­C and C­-H σ­bonds are strong

• C-­C bonds are non­-polar

• electronegativity of C and H are so similar that C-­H bonds can be considered non­-polar too

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Combustion of Alkanes

Complete Combustion

All alkanes react with a plentiful supply of oxygen to produce carbon dioxide and water.

eg CH4 (g) + 2O2 (g) = CO2 (g) + 2H2O (l) 

Incomplete Combustion 

In a limited supply of oxygen, there is not enough oxygen for complete combustion, carbon monoxide or carbon (soot) particulates can form instead

eg CH4 (g) + 1 1/2O2 (g) = CO (g) + 2H2O (l)

eg CH4 (g) + 1 O2 (g) = C (g) + 2H2O (l)

All combustion reactions are exothermic reactions

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