Alkanes Flashcards
What is an alkane
A saturated hydrocarbon
What type of bonds are formed between atoms in alkanes
sigma bonds
What is a sigma bond
A bond between 2 atoms formed when 1 orbital from each atom overlaps each other
Why do pairs of electrons repel each other
Because sigma bonds between carbon atoms and hydrogen atoms cause a repulsion
What angle is made by atoms in an alkane
109.5 degrees
What allows atoms to freely rotate in an alkane
Sigma bonds allow rotation to occur as they act as an axes
How is crude oil separated
fractional distillation towers
How does a fractional distillation tower separate hydrocarbons from crude oil
Crude oil turned into gas and gas enters tower where it rises, temperature changes so different boiling points of hydrocarbons lead to them becoming liquids`
What effect does chain length have on alkanes
The longer the chain, the larger the surface area of the molecule meaning more London forces can be formed between the molecules
What are London forces
weak intermolecular force
How does branching effect the chain length of alkanes
Branching lowers boiling point because the surface area is smaller so London forces don’t form as regularly
How reactive are alkanes with reagents
not very
Why are alkanes not very reactive with reagents
strong sigma bonds, no polarity mean that alkanes are not very reactive with reagents
Alkanes react really well with _____
oxygen
How does combustion occur with alkanes
when alkanes meet oxygen
What is released in complete combustion
carbon dioxide + water ( + energy )
Why are alkanes good fuels
They’re readily available, easily transportable, don’t produce any toxic products
What is complete combustion
when alkanes react with a plentiful supply of oxygen
what is incomplete combustion
when an alkane reacts with a little supply of oxygen
What are the 2 possible products that can from in incomplete combustion
soot (solid carbon)
carbon monoxide
What is carbon monoxide
An odourless, colourless, toxic gas that damages the body
Why is carbon monoxide bad for you
Because the carbon monoxide combines with oxygen which provides little space for oxygen to be carried around
How does an alkane form a haloalkane (mechanism)
free radical substitution
What is needed to break a halogen-halogen bond
UV light
What are the types of steps in free radical substitution
Initiation, Propagation, Termination
What is formed as a result of Homolytic fission
2 radicals
What is a radical
an unpaired atom
How reactive are radicals
extremley
What happens in the initiation step in a free radical substitution
The halogen-halogen bond breaks
What happens in the termination step
2 radicals react ending the whole process
What are the 2 main limitations of free radical substitution
Further substitution can occur or the halogen can be substituted at different positions
How do further substitutions occur in free radical substitution
A halogen radical can hit another hydrogen out of a molecule forming a hydrogen radical
How is a sigma bond positioned
on a line exactly between the 2 atoms
what shape does a carbon atom and its hydrogen atoms form
3D Tetrahedral shape
What state do London forces work in
solid and liquid
what holds alkanes together in liquid and gases
weak London forces
