Alkanes
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What are alkanes the main component of?
Natural Gas Crude Oil
What is the general formula of alkanes?
C(n)H(2n+2)
What is a sigma bond?
The result of the overlap of two orbitals, one from each bonding atom, with each overlapping orbital containing one electron.
What is the shape and bond angle around each carbon in an alkane?
Tetrahedral, 109.5
Are sigma bonds rigid?
No, rotation around atom is free and movement can occur
How does fractional distillation work?
Separation by boiling points, different alkanes of different chain lengths have different boiling points so can be separated
How does boiling point change as chain length changes?
Increases Larger surface area Greater surface area of contact London forces greater Requires more energy to overcome
What affect does branching have on boiling point?
Decreases boiling point Fewer surface area points of contact so fewer London forces Molecules can’t get as close decreasing intermolecular forces
What are the three reasons for lack of reactivity of the alkanes?
Sigma bonds are strong C-C bonds are non polar Electronegativity value of C and H are so similar they can be seen to be non-polar
What are the products of complete combustion?
Carbon Dioxide and Water
What two products can be formed in incomplete combustion?
Carbon Monoxide Carbon
When do alkanes react with halogens?
In the presence of UV light
What are the three steps of radical substitution?
Initiation Propagation Termination
What happens in the initiation step?
The covalent bond in the halogen molecule is broken by homolytic fission Forms two halogen radicals
Where does the energy come from for homolytic fission in radical substitution?
UV light
How many propagation steps are there?
2
When does a propagation reaction get terminated?
When two radicals collide or all reactants are used up
What happens in the termination stage?
Two radicals collide Forms a molecule with all electrons paired
What are the 2 limitations of radical substitution?
Further Substitution Substitution at different points on the carbon chain