Video Transcript
In general, which of the following statements is true? (A) The amount of energy required to promote an electron from one energy level to a higher energy level increases as we go farther from the nucleus. (B) The amount of energy required to promote an electron from one energy level to a higher energy level decreases as we go farther from the nucleus. Or (C) the amount of energy required to promote an electron from one energy level to a higher energy level remains constant as we go farther from the nucleus.
To answer this question, we must determine how the amount of energy required changes when the electron being promoted is farther from the nucleus. While we now know that atoms are very complex structures and their electrons are not confined to circular orbits around the nucleus, as was suggested by Bohr’s model of the atom, instead the modern theory of the atom now tells us that there are regions of high electron density surrounding the nucleus called electron clouds. However, electrons do still occupy areas of different energy levels around the nucleus. So even with its limitations, we can use Bohr’s model of the atom to answer this question.
Electrons close to the nucleus are very stable and because of their proximity to the positively charged nucleus experience a very strong electrostatic attraction. Electrons farther from the nucleus experience less electrostatic attraction to it. Generally, as an electron’s distance from the nucleus increases, the electrostatic attraction it experiences decreases. Because electrons farther from the nucleus are more loosely bound, the energy required to promote it to a higher energy level is much less than the energy that would be needed to promote an electron very close to the nucleus and thus more tightly held.
Using this information, we can eliminate answer choice (A), which states that more energy would be required to promote an electron farther from the nucleus. We can also eliminate answer choice (C), which states that the energy required would remain constant. Therefore, in general, the statement that is true is answer choice (B). The amount of energy required to promote an electron from one energy level to a higher energy level decreases as we go farther from the nucleus.