Faraday’s invention of the gas discharge tube launched two important avenues of inquiry:

• Atomic structure.

• Atomic spectra.

Atomic spectra had to be related to atomic structure, but no one could understand how. Classical physics could not explain

• The stability of matter.

• Discrete atomic spectra.

• Continuous blackbody spectra.

Thomson found that cathode rays are negative subatomic particles. These were soon named electrons. Electrons are

• Constituents of atoms.

• The fundamental units of negative charge.

Rutherford discovered the atomic nucleus.

His nuclear model of the atom proposes

• A very small, dense positive nucleus.

• Orbiting negative electrons.

Later, different isotopes were recognized to contain different numbers of neutrons in a nucleus with the same number of protons.

The spectra emitted by the gas in a discharge tube consist of discrete wavelengths.

• Every element has a unique spectrum.

• Every spectral line in an element’s absorption spectrum is present in its emission spectrum, but not all emission lines are seen in the absorption spectrum.

The wavelengths of the hydrogen emission spectrum are

• The spectrum is continuous.

• The spectrum depends only on an object’s temperature.

• Wien’s law: The peak intensity occurs at $\text{λ}\left(\text{in nm}\right)=(2.90\times {10}^6\text{nm}\text{K})\text{/}T$.