Topic B3 - Alkanes
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Why do longer chained alkanes have a higher BP?
-surface area increases, there are more points of contact between molecules -more electrons -more London Forces -more energy required to break/ overcome forces
Why do alkanes have relatively low boiling point?
-simple molecular compounds -weak intermolecular forces -which require little energy to overcome
Why do branched alkanes have a lower boiling point?
-fewer points of contact between molecules -so less energy is required to break the London Forces
What is a free radical?
species with an unpaired electron (e.g. a chlorine atom)
What is the initiation step of free radical substitution?
-starts off reaction -needs UV light -breaks the longest/ weakest bond
Initiation step example with Cl2
Cl2 —> 2Cl.
What is the propagation step of a free radical substitution?
uses both reactants and generates both products
What is the termination step of a free radical substitution?
takes all free radicals and gets rid of them
What are the 3 problems with free radical substitution?
-don’t know which carbon the substitution has taken place on -unwanted side products can be made in the termination step -multiple substitution reactions can occur, making it difficult to control (can be stopped by putting it in the dark)
What type of covalent bonds are between each atom in an alkane?
sigma bond
What is the definition of a covalent bond?
shared pair of electrons
What is a sigma bond?
result of overlap of 2 orbitals, one from each bonding atom (with each overlapping orbital containing 1 electron)
What is the bond angle between each bonded atom in an alkane?
109.5