3.4.3—Heterolytic fission
- Syllabus
- First assessment 2025
- Objective
- 3.4.3
- Level
- SL
Heterolytic Fission
In heterolytic fission both bonding electrons remain with one fragment, producing ions. Curly arrows show movement of an electron pair.
Place the curly-arrow tail on the bond being broken and its head on the fragment receiving both electrons. Then assign charges from electron ownership: heterolysis creates ions, unlike homolysis, which gives one electron to each radical.
Showing Electron-Pair Movement
Assessment in practice
Representative question
Question 1
[Maximum number: 2]
Contrast homolytic and heterolytic fission.
Homolytic fission:
Heterolytic fission:
Homolytic fission: each atom receives one «bonding» electron «when bond breaks»
OR
generates «neutral» free radicals
Heterolytic fission: one atom receives both «bonding» electrons «when bond breaks»
OR
generates «charged» ions
Marking guidance:
Award [1 max] if correct descriptions are reversed.
Electron-Pair Sharing Summary
Retrieve the route: classify nucleophiles and electrophiles, show heterolysis, write substitution and addition mechanisms, map Lewis coordination, compare SN1/SN2, and restore aromaticity in benzene substitution.
Check electron-pair arrow origin and destination, leaving-group departure, intermediate identity, carbocation stability and the assessed mechanism boundary.