4.1.2 Alkanes Flashcards
How many covalent bonds do alkanes have?
4 which are called sigma bonds
When does a sigma bond occur?
A sigma bond is the result of the head on overlap of orbitals
What shape does an alkane have and the bond angle?
Each carbon atom is surrounded by 4 electron pairs in four sigma bonds. Repulsion between these electron pairs result a Tetrahedral with bond angles of 109.5
What intermolecular forces do alkanes have?
London forces
What is the effect of chain length on boiling points?
> As the chain length increases, molecules have a larger surface area
So more surface contact is possible between molecules.
London forces between the molecules will be greater and so more energy is required to overcome the forces
What is the effect of branching on boiling points?
> The more branched a compound is, the fewer surface area interactions there are between molecules
This is because the molecules cannot fit together therefore fewer london forces.
This leads to branched molecules having a lower boiling point.
Why do alkanes have a low reactivity?
> all the covalent bonds in alkane molecules have high bond enthalpies - a large amount of energy is required to break the bonds
The carbon - hydrogen sigma bond have very low polarity because the electronegativities of carbon and hydrogen are almost the same
Equation of complete combustion of alkanes with methane
CH4 (G) + 2O2 (G) –> CO2 (G) + 2H2O (L)
What is the equation top balance complete combustion
CxHy + (x + y/4)O2 –> xCO2 + y/2H2O
When does incomplete combustion occur?
When there is a limited supply of oxygen
What are the three steps of radical substitution
1) Initiation
2) Propagation
3) Termination
Propagation of CH4 + CL
CH4 + Cl* –> CH3* + HCL
CH3* + Cl2 –> CH3CL + CL*
