Reactivity 3.4 Electron-pair sharing reactions (HL)
Reactivity 3.4.6 and 3.4.7
​Understandings:
  • A Lewis acid is an electron-pair acceptor and a Lewis base is an electron-pair donor (3.4.6).
  • When a Lewis base reacts with a Lewis acid, a coordination bond is formed. Nucleophiles are Lewis bases and electrophiles are Lewis acids (3.4.7).
Learning outcomes:
  • Apply Lewis acid–base theory to inorganic and organic chemistry to identify the role of the reacting species (3.4.6)
  • Draw and interpret Lewis formulas of reactants and products to show coordination bond formation in Lewis acid–base reactions (3.4.7).
Linking question(s):
  • Reactivity 3.1 What is the relationship between Brønsted–Lowry acids and bases and Lewis acids and bases?​
  • Structure 2.2 Do coordination bonds have any different properties from other covalent bonds?
This video covers the Lewis theory of acids and bases. 
This video is a comparison of the Bronsted-Lowry and Lewis theories. 
Reactivity 3.4.8
Understandings:
  • Coordination bonds are formed when ligands donate an electron pair to transition element cations, forming complex ions.
Learning outcomes:
  • Deduce the charge on a complex ion, given the formula of the ion and ligands present.
This video covers the formation and structure of complex ions. 
This video covers ligands.
This video covers how to deduce the charge on a complex ion. 
Reactivity 3.4.9
Understandings:
  • Nucleophilic substitution reactions include the reactions between halogenoalkanes and nucleophiles.
Learning outcomes:
  • Describe and explain the mechanisms of the reactions of primary and tertiary halogenoalkanes with nucleophiles.
Additional notes:
  • Distinguish between the concerted one-step SN2 reaction of primary halogenoalkanes and the two-step SN1 reaction of tertiary halogenoalkanes. Both mechanisms occur for secondary halogenoalkanes.
  • The stereospecific nature of SN2 reactions should be covered.
Linking questions:
  • Reactivity 2.2 What differences would be expected between the energy profiles for SN1 and SN2 reactions?
  • Reactivity 2.2 What are the rate equations for these SN1 and SN2 reactions?
This video is an introduction to nucleophilic substitution reactions. 
This video covers the SN1 and SN2 mechanisms.
This video is a comparison of the SN1 and SN2 mechanisms.
The video covers the stereochemistry of SN reactions. 
Reactivity 3.4.10
Understandings:
  • The rate of the substitution reactions is influenced by the identity of the leaving group.
Learning outcomes:
  • Predict and explain the relative rates of the substitution reactions for different halogenoalkanes.
Additional notes:
  • Different halogenoalkanes should include RCl, RBr and RI. 
  • The roles of the solvent and the reaction mechanism on the rate will not be assessed.
Linking questions:
  • Structure 3.1 Why is the iodide ion a better leaving group than the chloride ion?
Video coming soon.
Reactivity 3.4.11
Understandings:
  • Alkenes readily undergo electrophilic addition reactions.
Learning outcomes:
  • Describe and explain the mechanisms of the reactions between symmetrical alkenes and halogens, water and hydrogen halides.​
This video covers electrophilic addition reactions of the alkenes. 
Reactivity 3.4.12
Understandings:
  • The relative stability of carbocations in the addition reactions between hydrogen halides and unsymmetrical alkenes can be used to explain the reaction mechanism.
Learning outcomes:
  • Predict and explain the major product of a reaction between an unsymmetrical alkene and a
    hydrogen halide or water.
This video covers Markovnikov's rule.
Reactivity 3.4.13
Understandings:
  • Electrophilic substitution reactions include the reactions of benzene with electrophiles.
Learning outcomes:
  • Describe and explain the mechanism of the reaction between benzene and a charged electrophile, E+.
Additional notes:
  • The formation of the electrophile will not be assessed.
Linking questions:
  • Structure 2.2 What are the features of benzene, C6H6, that make it not prone to undergo addition reactions, despite being highly unsaturated?
  • Reactivity 3.1 Nitration of benzene uses a mixture of concentrated nitric and sulfuric acids to generate a strong electrophile, NO2 . How can the acid/base behaviour of HNO3 in this mixture be described?
This video covers the nitration of benzene. Note that the equation for the formation of the nitronium ion (the electrophile) is no longer required.