Question 1

Why do atoms have discrete energy levels instead of continuous ones?

Accepted Answer

This is a fundamental consequence of quantum mechanics. The wave-like nature of electrons means they can only form stable standing waves when confined in an atom's potential well. These stable states correspond to specific, discrete energy values.

Question 2

How can line spectra be used to identify elements in stars?

Accepted Answer

Starlight is a continuous spectrum. As it passes through the star's cooler outer atmosphere, atoms in the atmosphere absorb photons at their characteristic frequencies, creating an absorption spectrum. By matching these dark lines to the known spectra of elements, we can determine the star's chemical composition.

Question 3

What's the main difference between an emission and an absorption spectrum?

Accepted Answer

An emission spectrum shows bright lines (photons emitted by excited atoms), while an absorption spectrum shows dark lines (photons absorbed by atoms) against a continuous background. Both sets of lines occur at the exact same wavelengths for a given element.

Question 4

Can an electron absorb a photon with more energy than an excitation gap?

Accepted Answer

No. For an electron to be excited to a higher bound level, the photon's energy must match the energy gap *exactly*. If the photon's energy is too high or too low, it will not be absorbed. The only exception is if the photon has enough energy to completely remove the electron (ionisation), in which case any excess energy becomes the kinetic energy of the freed electron.

Energy levels in atoms and line spectra

What you need to know

Energy levels in atoms and line spectra