Chapter 12 - Alkanes Flashcards
What are alkanes?
Saturated hydrocarbons
General formula of alkanes
Cn H2n+2
What will every carbon atom in an alkane have?
Four single bonds with other carbon atoms
What are saturated hydrocarbons?
All carbon-carbon bonds are single
What is the name of the bond between the carbon atoms in an alkane?
A sigma bond
What is a sigma bond?
The result of an overlap of two orbitals, one from each bonding atom
How many electrons are in a sigma bond?
2
Where is a sigma bond positioned?
On a line directly between two bonding atoms
What are the two bonds where sigma bonds can occur?
C-H or C-C
What is the bond angle in an alkane and why?
109.5, the four pairs of bonding electrons repel eachother equally
What structure does an alkane form?
A tetrahedral structure
Why are alkanes not rigid?
The sigma bonds act as an axes which the shape can rotate around
How is crude oil separated into fractions?
Fractional distillation
As chain length increases, what happens to the boiling point of alkanes?
It increases
Why does fractional distillation work?
Alkanes have different boiling points, dependent on chain length
What type of bonds are responsible for the boiling point of alkanes?
London forces between the molecules
Where are covalent bonds found?
Inside molecules
Where are London forces found?
Between molecules
Why do alkanes with a longer chain length have higher boiling points?
The longer the carbon chain, the larger the surface area available over which London forces can act. There are also more electrons to interact. This means more energy is needed to overcome the London forces
Will branched isomers have higher or lower boiling points?
Lower
Why do branched chain alkanes have lower points?
The chains can’t pack as closely together. There are fewer points of contact and a smaller surface area of the molecules, so the London forces are weaker
Why are alkanes very unreactive? (3)
C-C and C-H sigma bonds are very strong
C-C bonds are non-polar
Carbon and hydrogen have similar electronegativities, so the C-H bond is considered non-polar
What products are produced when an alkane reacts completely with oxygen?
Carbon dioxide and water
What is the name of the reaction between oxygen and alkanes?
Combustion