Chapter 12 Flashcards
Where are alkanes found?
They are found in crude oil deposits as they lack reactivity.
How do you separate alkanes?
A fractional column is used in order to extract them, small molecules with lower boiling points travel to the top before they separated. Whereas the larger molecules with high boiling points are separated at the bottom.
What is the general formula for an alkane?
CnH2n+2
How are alkanes bonded?
As they are saturated they are joined to 4 other atoms by sigma bonds.
What is a sigma bond?
Sigma bond is the result of the overlap of two orbitals one from each bonding atom. Each overlapping orbital contains one electron so the Sigma bond has two electrons that are shared between the bonding atoms.
What is the shape of an alkane?
Each carbon atom is surrounded by four electron pairs with four Sigma bonds. The position result in a 3D tetrahedral arrangement around each carbon atom with a bond angle of approximately 109.5°. The sigma bond acts as axes around which the atoms can rotate freely.
What happens as the chain length increases?
The boiling point of the alkane also increases as the molecules have a larger surface area so more surface contact is possible between the molecules. The London forces will be greater so more energy is required to overcome the forces.
What forces are found between the molecules in an alkane.
As they are non polar they have London forces which are weak.
What does the effect of branching have on the boiling point?
More branching decreases the boiling point as there are fewer surface points of contact between the molecules giving fewer London forces. Additionally the branches get in the way and prevent branch manager is getting his closest straight-chain is decreasing the intermolecular forces further.
Why do alkanes lack reactivity
As the C-C bonds are non polar and the C-C and C-H sigma bonds are strong. The electronegativity of carbon and hydrogen are so similar that the C-H bond is considered to be non-polar.
What do alkanes produce when in a plentiful supply of oxygen during combustion?
Carbon dioxide and water
What happens when there is a limited supply of oxygen during combustion?
It is incomplete therefore carbon monoxide or carbon can be produced.
For every CH2 how many extra oxygen molecules do you need?
1 1/2 molecules.
What is radical substitution?
It is a very reactive species. An atom or group of atoms with a unpaired electron formed by homolytic fission. It becomes a substitution reaction as the H in the alkane is replaced with another atom or group of atoms
What is the mechanism for the bromination of the methane?
Radical substitution
