what is an atomic spectrum?
- the distribution of light intensity emitted or absorbed by atoms at specific wavelengths
what are spectral lines?
- discrete wavelengths of light emitted or absorbed by atoms
why do atoms produce line spectra instead of continuous spectra?
- because electrons can only occupy quantised energy levels
what happens in an emission spectrum
- electrons fall to lower energy levels and emit photons
what happens in an absorption spectrum?
- electrons absorb photons and jump to higher energy levels
what is the Rydberg Formula
1/λ = R ( 1/m^2 - 1/n^2 )
what do m and n represent in the Rydberg Formula?
- initial and final electron energy levels
what are the three main hydrogen spectral series?
- Lyman ( UV ) n = 1
- Balmer ( visible ) n = 2
- Paschen ( infrared ) n = 3
what did Niels Bohr propose about electron orbits?
- electrons can only exist in discrete energy levels
what happens when an electron changes energy level?
- a photon is emitted or absorbed
what is the photon energy relation in atomic transitions?
hv = Ef - Ei
what is Bohr’s angular momentum quantisation rule?
L = nħ
what is the Bohr radius?
ao = 0.53Å
what are the allowed orbit radii in the Bohr model?
rn = n^2ao
where ao = Bohr radius
what are the allowed energy levels of hydrogen in the Bohr model?
En = - 13.6eV / n^2
why are Bohr energies negative?
- because the electron is bound to the nucleus
what is De Broglies Hypothesis ?
- all particles have wave like properties
what is the de Broglie wavelength equation?
λ = h / p or h / mv
what happens to wavelength if momentum increases
- the wavelength decreases
how did de Broglie explain Bohr’s quantised orbits?
- electron waves must form standing waves around the orbit
what condition must be satisfied for a stable orbit?
2pir = n λ
How did de Broglie’s idea lead to Bohr’s rule?
using λ=h/p, and 2pir = n λ gives L = nħ
which experiment confirmed electron wave behaviour?
- the Davisson-Germer electron diffraction experiment
when are quantum effects important in gases?
- when the de Broglie wavelength is comparable to the distance between particles
