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Question Video: Identifying the Equation Which Corresponds to the Greatest Ionization Energy Chemistry • Second Year of Secondary School

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Which of the following equations is likely to correspond to the greatest ionization energy? [A] F(g) ⟶ F⁺(g) + e⁻ [B] B(g) ⟶ B⁺(g) + e⁻ [C] N(g) ⟶ N⁺(g) + e⁻ [D] Li(g) ⟶ Li⁺(g) + e⁻ [E] Na(g) ⟶ Na⁺(g) + e⁻

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Video Transcript

Which of the following equations is likely to correspond to the greatest ionization energy? (A) F, gas, reacts to produce F+, gas, plus e−. (B) B, gas, reacts to produce B+, gas, plus e−. (C) N, gas, reacts to produce N+, gas, plus e−. (D) Li, gas, reacts to produce Li+, gas, plus e−. Or (E) Na, gas, reacts to produce Na+, gas, plus e−.

In this question, we must identify the equation that likely corresponds to the highest ionization energy. Let us first describe the term “ionization energy.” Ionization energy is the amount of energy required to remove the most loosely bound electron completely from an isolated gaseous atom. We should appreciate that ionization energy depends on the position in the periodic table since it depends on atom size.

The elements on the left side of the table have a relatively large radius, so there is a reasonable distance between their nucleus and most loosely bound electrons. It is relatively easy to remove one electron from these chemical elements, and we do not need much energy.

The equation in (D) describes the first ionization energy of lithium. There is a large distance between the lithium nucleus and the outermost lithium electron, in comparison to the other period two elements. This means that the ionization energy is low. For this reason, answer choice (D) is not the answer to this question.

The elements on the right side of the table have a relatively small radius. They usually have less space between their nucleus and most loosely bound electrons. Fluorine has a high first ionization energy because fluorine atoms have a small radius. There are strong forces of electrostatic attraction between its nucleus and most loosely bound electrons. As fluorine is furthest right of the given period two elements, we can deduce that it would have a higher first ionization energy than nitrogen or boron. For this reason, we can eliminate answer choices (B) and (C).

We should appreciate that ionization energy should decrease down a group since atom size increases. Thus, sodium should have a low ionization energy. Sodium should have the widest atoms and the lowest ionization energy of all the answer choices. For this reason, we can rule out answer choice (E).

As fluorine has the smallest atoms and the highest ionization energy, the equation that is likely to correspond to the greatest ionization energy is (A): F, gas, reacts to produce F+, gas, plus e−.

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