Question detail
Which of the following statements correctly describes 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
Atomic structure
Question
- A. It increases down a group in the periodic table.
- B. It decreases across a period from left to right.
- C. It is always a positive value.
- D. It is the same for all elements.
Answer
It is always a positive value.
Explanation
First ionisation energy is always a positive value because energy must be supplied to overcome the attraction between the negatively charged electron and the positively charged nucleus.
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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