Question detail
What trend in first ionisation energy is observed across Period 3 elements?
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. It remains constant.
- B. It decreases.
- C. It increases.
- D. It fluctuates.
Answer
It increases.
Explanation
As you move across Period 3, the first ionisation energy increases due to the increasing nuclear charge, which attracts the electrons more strongly, making them harder to remove.
Common mistake
Confusing Ionisation Energy Definition
Students often confuse first ionisation energy with other forms of energy, such as total energy or binding energy.
First ionisation energy is defined as the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions. To clarify, remember the formula: Ionisation Energy = Energy required to remove an electron from an atom. For example, for a sodium atom (Na), the first ionisation energy can be expressed as Na(g) → Na⁺(g) + e⁻. This shows that energy is needed to remove the electron, which is the essence of ionisation energy.
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