Question detail
What is the first ionisation energy of an element?
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. The energy required to remove the first electron from a neutral atom.
- B. The energy required to remove all electrons from an atom.
- C. The energy released when an electron is added to an atom.
- D. The energy required to ionise a molecule.
Answer
The energy required to remove the first electron from a neutral atom.
Explanation
The first ionisation energy is defined as the energy needed to remove the outermost electron from a neutral atom in its gaseous state, reflecting the atom's stability.
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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