Electromagnetic Radiation, Quantum Mechanics, and Atomic Models

What are the three characteristics of electromagnetic radiation?

Wavelength (λ), frequency (ν), and velocity (c).

What is wavelength (λ)?

The distance between two peaks or troughs of a wave.

What is frequency (ν)?

The number of wave cycles per second that pass a given point.

What is the speed of light in a vacuum?

c = 299,792,458 m/s.

What is the relationship between photon energy, frequency, and wavelength?

E = hν = hc/λ.

What is Planck's quantization hypothesis?

Energy is not continuous; electronic oscillator energies occur in discrete amounts: E = nhν.

What is Planck's constant?

h = 6.626 × 10⁻³⁴ J·s.

What was the ultraviolet catastrophe?

Classical physics predicted that blackbody radiation would increase without bound at high frequencies, which did not happen.

What is the photoelectric effect?

The emission of electrons from a metal surface when light shines on it.

What is threshold frequency (ν₀)?

The minimum frequency required to eject an electron from a particular metal.

What is the work function (φ)?

The energy required to remove an electron from a metal surface.

What is Einstein's photoelectric equation?

KEₑ = hν − φ.

How are work function and threshold frequency related?

φ = hν₀.

How does photon energy change with frequency?

Higher frequency → higher photon energy.

How does photon energy change with wavelength?

Higher wavelength → lower photon energy.

What did J.J. Thomson discover?

He determined that cathode rays were composed of electrons.

What did Millikan's oil-drop experiment determine?

The charge of the electron.

What are atomic number (Z) and mass number (A)?

Z = number of protons; A = number of protons + neutrons.

Why was the classical nuclear model of the atom unstable?

An accelerating electron should radiate energy, lose energy, and eventually spiral into the nucleus.

What is a line spectrum?

A spectrum containing only specific, discrete wavelengths.

What does an atomic emission spectrum show?

Light emitted when an atom moves from a higher energy state to a lower energy state.

What did Bohr's model propose?

Electrons in hydrogen can exist only in certain allowed energy levels/orbits.

What is the Bohr energy equation?

E = −2.18 × 10⁻¹⁸ J × Z²/n².

What happens when an electron absorbs energy?

It moves from a lower energy state to a higher energy state.

What happens when an electron emits energy?

It moves from a higher energy state to a lower energy state.

What is the ground state?

The lowest possible energy state.

What is an excited state?

Any state that is not the lowest possible energy state.

What is the de Broglie equation?

λ = h/mv.

What is wave-particle duality?

Light can behave as a wave or as particle-like photons, and de Broglie proposed that matter can also have wave-like properties.

What is the Heisenberg Uncertainty Principle?

There is a fundamental limit to how precisely both a particle's position and momentum can be known simultaneously: Δx·Δ(mv) ≥ h/4π.