12.1
Sigma bond (σ) A bond formed by the overlap of one orbital
from each bonding atom, consisting of 2
electrons and with the electron density centred
around a line directly between the nuclei of the
two atoms.
How are alkanes extracted Fractional distillation
Property of a sigma bond Acts as axes around which the atoms can rotate
freely, so these shapes are not rigid.
Explain the effect of chain length on boiling London forces act between molecules that are in
point close surface contact. As the chain length
increases, the molecules have a larger surface
area, so more surface contact is possible between
molecules. The London forces between the
molecules are greater and so more energy is
required to overcome the forces
Shape and bond angle of alkanes Tetrahedral 109.5°
How many electrons does each sigma bond 2
have between bonding atoms?
Where is a sigma bond positioned On a line directly between the bonding atoms
Explain the effect of branching on boiling point There are fewer points of contact between
molecules of branches alkanes, giving fewer
London forces. Another factor lies with the
shape of the molecules. The branches get in the
way and prevent the branches molecules getting
close together as straight-chain molecules,
decreasing the intermolecular forces further.
12.2
List three reasons why alkanes are not very C-C and C-H σ bonds are strong
reactive C-C bonds are nonpolar
The electronegativity of carbon and hydrogen is
so similar that the C-H bond can be considered
to be non-polar
What type of reaction are all alkanes able to Combustion
react in?
What are alkanes used as and why? Fuels because they are readily available, easy to
transport and burn in a plentiful supply of
oxygen without releasing toxic products.
Sigma bond (σ) A bond formed by the overlap of one orbital
from each bonding atom, consisting of 2
electrons and with the electron density centred
around a line directly between the nuclei of the
two atoms.
How are alkanes extracted Fractional distillation
Property of a sigma bond Acts as axes around which the atoms can rotate
freely, so these shapes are not rigid.
Explain the effect of chain length on boiling London forces act between molecules that are in
point close surface contact. As the chain length
increases, the molecules have a larger surface
area, so more surface contact is possible between
molecules. The London forces between the
molecules are greater and so more energy is
required to overcome the forces
Shape and bond angle of alkanes Tetrahedral 109.5°
How many electrons does each sigma bond 2
have between bonding atoms?
Where is a sigma bond positioned On a line directly between the bonding atoms
Explain the effect of branching on boiling point There are fewer points of contact between
molecules of branches alkanes, giving fewer
London forces. Another factor lies with the
shape of the molecules. The branches get in the
way and prevent the branches molecules getting
close together as straight-chain molecules,
decreasing the intermolecular forces further.
12.2
List three reasons why alkanes are not very C-C and C-H σ bonds are strong
reactive C-C bonds are nonpolar
The electronegativity of carbon and hydrogen is
so similar that the C-H bond can be considered
to be non-polar
What type of reaction are all alkanes able to Combustion
react in?
What are alkanes used as and why? Fuels because they are readily available, easy to
transport and burn in a plentiful supply of
oxygen without releasing toxic products.
