Alkanes 4.12 Flashcards
What are alkanes?
Alkanes are saturated hydrocarbons that are main components of natural gas and crude oil.
What effect has alkane being stable has on crude oil deposits
Because of its lack of reactivity it has allowed crude oil deposits to remain in the earth for millions of years.
Sigma bond
A sigma bond is the result of the overlap of two orbitals, one from each bonding atom
What does the sigma bond do for the atoms?
It is a type of covalent bond which acts as an axes so the atoms can rotate freely.
What happens to the boiling point if you increase the chain length?
Longer chain = more atoms = more electrons = stronger induced dipole-dipole/London forces= increased attraction between the molecules = more energy required to overcome the bonds
Why does the boiling point increase when chain length increase?
There is a greater points of contact so there is more places in which london forces could be formed, resulting in stronger london forces.
What happens to the boiling point when the chain becomes more branched?
The boiling point decreases because there is a less points of contact so there is less places where london forces can form resulting in weaker london forces.
Why do alkanes not react with common reagents?
-C-C and C-H bonds are strong
-C-C bonds are non-polar
-The electronegativity of C and H is so similiar that the C-H bonds could be conisdered non polar.
Complete Combustion
Oxidising a suel in a plentiful supply of oxygen and air.
complete combustion
alkane + oxygen -> carbon dioxide + water
incomplete
alkane + oxygen -> carbon monoxide + water
alkane + oxygen -> carbon + water (low supply of oxygen)
Radical
A species with an unpaired electron
Step 1 - Intiation
Homolytic fission of halogen
Br2 —> Br• + Br•
Step 2 - Propagation
X Radical + Alkane -> Alkane radical + HX (step 1)
Alkane radical + X2 -> Haloalkane + X• (step 2)
Termination
Two radicals join, both radicals collide and reeact and are removed stopping the reaction.
•Br + •Br —> Br2
•CH3 + •Br —> C2H6
