Chapter 12 (approved) Flashcards
What are alkanes mainly used as?
Fuels, they are the main components of natural gas and crude oil
How reactive are alkanes?
Very stable/ not very reactive
Sigma bond
A single covalent bond which is the result of the head on overlap between two orbitals
Covalent bond
Shared pair of electrons
What causes sigma bonds, and where are they positioned?
The head on overlap of two orbitals, one from each bonding atom
Each overlapping orbital has 1 electron so the sigma bond has 2 electrons shared between the bonding atoms
A sigma bond is positioned on a line directly between bonding atoms
Why are the shapes of alkanes not rigid?
Because the sigma bonds act as axis which the atoms can rotate around
How does boiling point change as chain length increases?
As chain length increases, the molecules have a larger SA of contact, so more London forces between them, so more energy is required to overcome them
How does boiling point change changed with more branches?
Less SA of contact, so less London forces, and less energy required to overcome them
Why are alkanes not very reactive?
C-H and C-C bonds are strong
C-C bonds are non-polar
C-H bonds can be considered as non-polar
Combustion of alkanes
When alkanes react with a plentiful supply of oxygen to form carbon dioxide and water, also giving out heat
Why are alkanes used as fuels?
Volatile, readily available, easy to transport, doesn’t form toxic products in a plentiful supply of oxygen
What happens when combustion of alkanes is incomplete?
Carbon (soot) or toxic carbon monoxide is formed
Reaction of alkanes with halogens
Halogen react with alkanes to form dihaloalkanes in the presence of sunlight due to the high energy UV radiation providing energy for the reaction
Radical substitution of alkanes 3 steps: bromine and methane
Step 1: Initiation
Br2 —> Br. + Br.
Step 2: Propagation
Propagation step 1:
CH4 + Br. —> CH3. + HBr
Propagation step 2:
CH3. +Br2 —> CH3Br + Br.
Step 3: Termination
Br. +Br. —> Br2
Ch3. + Ch3. —> C2H6
CH3. + Br. —> CH3Br
Limitations of radical substitution in organic synthesis
After the haloalkane is formed, further substitution may occur causing a mixture of haloalkanes with varying number of halogen atoms in it to form
