Electrons in Atoms - Part 1 Summary

Electromagnetic Radiation

  • Electromagnetic radiation is the emission and transmission of energy in waves.

  • c = λν where c is the speed of light (3.00 \times 10^8 m/s in vacuum), λ is wavelength, and ν is frequency.

  • Molecules interact with electromagnetic radiation through rotation (microwave), vibration (IR), translation (across spectrum), and electronic transition (UV).

  • Planck's equation: E = hν, where h is Planck's constant (6.626 \times 10^{-34} \text{ J s}).

Electromagnetic Wave Properties

  • Constructive interference: Waves in phase reinforce each other.

  • Destructive interference: Waves out of phase cancel each other.

  • Amplitude determines light intensity.

  • Waves exhibit reflection, refraction, diffraction, and polarization.

Atomic Spectra and the Bohr Atom

  • Atomic emission spectrum: Gas emits light when an electric current passes through it.

  • Absorption spectrum: White light passes through a gas, showing absorbed wavelengths.

  • Each element has a unique spectrum, useful for identification.

  • Rydberg equation: \frac{1}{λ} = RH \left( \frac{1}{n1^2} - \frac{1}{n_2^2} \right), relates wavelengths in the hydrogen spectrum.

  • Bohr's postulates:

    • Electrons exist in discrete energy levels without emitting radiation.

    • Electrons can move between energy levels, emitting or absorbing monochromatic radiation: \Delta E = hν.

    • Electron's angular momentum is quantized: mvr = \frac{nh}{2π}.

  • Bohr's theory correctly explains the H emission spectrum but fails for other elements.

Bohr Theory and Ionization Energy

  • Ionization energy is the energy to remove an electron from an atom.

  • For hydrogen-like species: En = -Z^2 \frac{RH}{n^2}; where Z is the atomic number

Photoelectric Effect

  • Light has both wave and particle nature.

  • Einstein's explanation: hν = KE + W, where KE is kinetic energy of ejected electron and W is the work function.

  • If hν > W, electrons are ejected; otherwise, they aren't.

Wave Nature of the Electron

  • De Broglie relationship: λ = \frac{h}{mv}, where λ is the wavelength of a particle.

  • Electrons exhibit wave-particle duality, verified by Davisson & Germer.

From Classical to Quantum

  • Classical mechanics describes particles with defined trajectories.

  • Quantum mechanics describes particles with probability distributions.

  • Bohr theory limitations led to modern quantum theory in 1926.