Chapter 28 - Physics Notes

Quantum Mechanics: The field of physics that studies the motion of subatomic particles.
Emission Spectrum: A pattern formed by the frequencies of radiation emitted from an ionized gas, unique for each element.
Absorption Spectrum: A unique pattern formed by a complete spectrum of light minus the frequencies absorbed by a particular gas through which light passes.
Energy Levels: The amount of energy at which electrons can orbit an atom stably without radiating.
Ground State: The condition in which all the electrons in an atom are at their lowest energy states.
Excited State: The condition in which some of the electrons in an atom are not at their lowest energy states.

The Bohr Atomic Model

Bohr proposed a new atomic model in which electrons of a given element are restricted to certain circular orbits.
Orbital radii are quantized, and the radius of each orbit is related to the orbits’ energy.
Electrons in the shell nearest the nucleus, energy level 1, have the least energy (E₁), a relatively large negative number.
If an electron’s energy is positive with respect to a nucleus, it is not bound to that nucleus.

We measure an electron’s energy in electron volts (eV), the energy required to move a fundamental charge through a potential difference of one volt.
When a single photon is emitted, it has an energy of E_phot = –(E_f – E_i) = hf.
Frequency of the emitted photon: f = –(E_f – E_i) / h.
For an electron to move to a higher energy level, it must gain energy: ΔE = E_f – E_i.
An electron must absorb a photon to move to a higher energy shell.

Each gas can radiate only certain frequencies.
Under certain conditions, the predictions of the classical theory are still correct (Correspondence principle).

Calculate the wavelength of a 75.0 kg Olympic sprinter running at 12.3 m/s.

m = 75.0 kg

v = 12.3 m/s

λ = h / mv

λ = 6.626 × 10^–34 J·s / (75.0 kg × 12.3 m/s)

λ = 7.18 × 10^–37 m