Question detail
Which element in Period 3 has the highest first ionisation energy?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Periodicity
Question
- A. Sodium
- B. Magnesium
- C. Aluminium
- D. Argon
Answer
Argon
Explanation
Argon has the highest first ionisation energy in Period 3 due to its complete outer shell, which makes it very stable and requires more energy to remove an electron.
Common mistake
Misunderstanding Ionisation Energy Trends
Students often confuse the trend in first ionisation energy across Period 3 with atomic radius, thinking that ionisation energy decreases as atomic radius increases.
To clarify, remember that first ionisation energy increases across Period 3 due to increased nuclear charge attracting electrons more strongly. Use the formula for ionisation energy trends: as atomic number increases, ionisation energy increases because of greater effective nuclear charge. Therefore, the correct trend is that first ionisation energy increases across Period 3.
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