CAIE A-Level Chemistry 1.4.6 Factors Affecting Ionisation Energy
Practise comparing ionisation energies through nuclear charge, radius, shielding, sub-shell energy and spin-pair repulsion.
- Syllabus
- 2028–2030
- Course
- Chemistry 9701
- Level
- AS
Practise comparing ionisation energies through nuclear charge, radius, shielding, sub-shell energy and spin-pair repulsion.
Table 1 gives physical data for some of the Period 3 elements.

Table 1
Explain the difference between the first ionisation energies of the elements with atomic numbers 11 and 17.
All 3 points correct scores two marks
Any 2 points scores one mark
- nuclear charge increases OR increasing proton number e.g. 17 / Cl has a greater nuclear charge
- describe the similarity in shielding between the two elements
e.g. they have almost the same shielding
- describe the overall effect in terms of greater nuclear attraction for (outer) electrons e.g. (outer) electrons are attracted more (strongly) to the nucleus
Explain the difference between the first ionisation energies of the elements with atomic numbers 15 and 16 .
M1 describes the difference between 1st IE of elements 15 and 16 ( P and S ) in terms of either: spin-pair repulsion (in element 16 / S ) OR electron pair repulsion (in element 16 / S )
M2 describes the location of the electron pair in the (3)p orbital which repel each other