Question detail
How does the first ionisation energy of magnesium compare to that of aluminium?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Atomic structure
Question
- A. Magnesium has a higher ionisation energy than aluminium.
- B. Aluminium has a higher ionisation energy than magnesium.
- C. They have the same ionisation energy.
- D. There is no clear trend.
Answer
Aluminium has a higher ionisation energy than magnesium.
Explanation
Aluminium has a higher first ionisation energy than magnesium due to its increased nuclear charge and the electron being removed from a higher energy level, which is further from the nucleus.
Common mistake
Misinterpreting ionisation energy trends
Students often think that ionisation energy increases steadily across a period and decreases down a group, ignoring the effect of subshell filling and electron shielding.
Explain that ionisation energy rises across a period due to increasing nuclear charge and decreasing atomic radius, but drops when a new subshell begins (e.g., from Na to Mg). Down a group, ionisation energy decreases because added electrons are farther from the nucleus and more shielded, reducing the energy required to remove an electron.
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