IB Chemistry R3.3 Organic chemistry - electron sharing reactions - radical substitution reactions

Guiding Question
What happens when reactants share their electron pairs with others?
Understandings
R3.4.1 A nucleophile is a reactant that forms a bond to its reaction partner (the electrophile) by donating both bonding electrons.
R3.4.2 In a nucleophilic substitution reaction, a nucleophile donates an electron pair to form a new bond, as another bond breaks producing a leaving group.
R3.4.3 Heterolytic fission is the breakage of a covalent bond when both bonding electrons remain with one of the two fragments formed.
R3.4.4 An electrophile is a reactant that forms a bond to its reaction partner (the nucleophile) by accepting both bonding electrons from that reaction partner.
R3.4.5 Alkenes are susceptible to electrophilic attack because of the high electron density of the carbon-carbon double bond. These reactions lead to electrophilic addition.