Question detail
Which of the following correctly describes the first ionisation energy trend in Period 3?
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. It decreases due to increased electron shielding.
- B. It increases due to decreased atomic radius.
- C. It remains constant due to similar atomic structures.
- D. It fluctuates due to varying electron configurations.
Answer
It increases due to decreased atomic radius.
Explanation
The first ionisation energy in Period 3 increases due to decreased atomic radius, which enhances the effective nuclear charge experienced by the outer electrons, making them more difficult to remove.
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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