C12 Alkanes Flashcards
What is the bonding like in an alkane?
2 p-orbitals, 1 from each bonding atom
overlap and contain 1 electron each
sigma bond has 2 electrons that are shared between bonding atoms
each carbon in an alkane has 4 sigma bonds
What is a sigma bond?
The head on overlap of 2 atomic orbitals 1 from each bonding atom, with electron density centred around a line directly between the bonding atoms nuclei.
How many bonds can a Carbon form in an alkane?
4 covalent bonds
Are alkanes saturated or unsaturated?
saturated hydrocarbons (single bonds only)
What is the general formula of an alkane?
CnH2n+2
What’s is the shape of an alkane?
tetrahedral
bond angle = 109.5*
caused by = each c atom surrounded by 4 e pairs in 4 sigma bonds, repulsion between these e pairs cause this shape around each C atom
Lone pairs repel more than bonding electrons
4 electron pairs in 4 sigma bonds (4 bonding pairs)
Why does BP of alkanes increase as chain length increases?
because of weak LFs
What is the effect of chain length on boiling point?
- chain length increases
- increases surface area
- Greater (stronger) London forces
- more energy required to overcome the forces
What’s is the effect of branching on boiling point?
(Example may include isomers of alkanes- branched isomers has lower boiling point than straight chain isomers)
- more branching
- fewer surface points of contact (decreased surface area)
- weaker (fewer) London forces
Also another reason is to do with the shape.
- branches get in the way and prevent branched molecules getting as close together as straight chain molecules, decreasing IMFs further
What is an alkane?
A saturated hydrocarbons containing C-H bonds only.
Are alkane bonds polar? Why/why not?
Non-polar because carbon and hydrogen have similar electronegativities.
Describe the sigma bond in alkane?
The sigma bond is a covalent bond which has a direct overlap of the electron clouds of the bonding atoms.
What type of intermolecular forces do alkanes have? Why?
London forces -> induced dipole-dipole interaction, because the bonds are non-polar
What happens to the boiling point as alkane chain length increases? Why?
BP increases
Increased surface area
Stronger LFs
more energy required to overcome LFs
Does branched have a lower/higher BP compared straight chain?
lower BP
have fewer surface area
less LFs
Are alkanes insoluble/soluble in water? Why?
Insoluble
bonds in H2O stronger than LFs in alkanes
How reactive are alkanes?
Very unreactive
What reactions will alkanes undergo?
Combustion and reaction with halogens
What is complete combustion?
Combustion in plentiful supply of oxygen
What are the products of complete combustion when alkanes are used?
Carbon dioxide and water
What is the colour of the Bunsen burner flame during complete combustion?
Blue flame
What is incomplete combustion and what products are formed in the case of alkanes?
Combustion in limited supply of O2
Products = H2O, CO2 and CO
What type of hydrocarbon are most likely to undergo incomplete combustion?
Long chain Hydrocarbons
What is the environmental impact of carbon monoxide?
It is toxic/poisonous