Explain that electrons change orbit when there is absorption or emission…

The idea

This statement asks you to explain a cause-and-effect link between electromagnetic radiation and electron orbits. An electron can move to an orbit further from the nucleus when the atom absorbs electromagnetic radiation; the absorbed energy raises the electron to a higher orbit. An electron can move to an orbit closer to the nucleus when the atom emits electromagnetic radiation; the emitted radiation carries away energy as the electron drops to a lower orbit. The key idea is that a change of orbit is always accompanied by absorption or emission of electromagnetic radiation, and the direction of the change tells you which happens. In a multiple-choice question, check that the option pairs absorption with moving further out and emission with moving closer in, and that it names electromagnetic radiation rather than an unrelated transfer.

What earns the marks

• Links absorption of electromagnetic radiation to an electron moving to a higher orbit.
• Links emission of electromagnetic radiation to an electron moving to a lower orbit.
• States that a change of orbit is accompanied by absorption or emission of electromagnetic radiation.
• Distinguishes the direction of the orbit change for absorption compared with emission.

Common mistakes and how to put them right

• Reverses the link by pairing absorption with a drop to a lower orbit.

  Put it right: Match absorption to a move further from the nucleus.

• Treats the orbit change as happening without radiation.

  Put it right: State that absorption or emission of electromagnetic radiation accompanies it.

• Names a non-electromagnetic transfer as the cause.

  Put it right: Identify electromagnetic radiation as what is absorbed or emitted.

Exam tips

• Decide first whether the electron moves out or in, then choose the matching absorption or emission option.
• Cross out options that reverse the absorption and emission pairings.
• Check that the chosen option mentions electromagnetic radiation, not just energy in general.