Arrangement of Electrons in the Atom

Niels Bohr

  • Provided an insight into the arrangement of electrons in the atom

Bohr theory

Spectra

Bohr theory 2

Note

Flame test

  • Carried out an experiment using hydrogen discharge tube-instead of seeing a continuous spectrum seen a series of narrow coloured lines
  • Light is emitted when an electric current is passed through hydrogen-emission line spectrum
  • Spread of colours is a continuous spectrum e.g rainbow
  • Each element has its own unique emission line spectrum
  • White light is passed through a glass prism light is broken up into an array of colours-spectrum
  • Spectrometer-instruments used to carry out experiments on spectra
  • Spectroscope-instruments used to observe spectra
  • Using a damp wooden splint hold a sample of salt in the blue flame of a bunsen burner
  • Lithium-Crimson
  • Potassium-Lilac
  • Barium-Green
  • Strontium-Red
  • Copper-Blue-green
  • Sodium-Yellow

Bohrs theory 3

  • Quantisation-electron in an atom can only have a fixed amount of energy(quantum)
  • Energy level-fixed energy value that an electron in an atom may have
  • Energy absorbed when electron jumps from n=1 to n=2
  • Energy emitted when electron falls from n=2 to n=1
  • Ground state-electrons occupy the lowest available energy levels
  • Excited state-electrons occupy higher energy levels than those available in the ground state
  • Provided energy by electricity or heating
    specific amount of this energy is absorbed electrons jump from lower energy levels to higher ones
  • Unstable fall back to lower energy levels after a short time
    Excess energy is released in the form of a photon of light has a definite amount of energy-light of a definite frequency
  • h-plancks constant
    f-frequency of light emitted
  • equation tells us that the energy difference is proportional to he frequency of the light emitted
  • Different numbers & type of electron transitions for each element. Give rise to a different emission line spectrum for each element

Series

  • n=1 Lyman series
  • n=2 Balmer series
  • n=3 Paschen series
  • Energy diff is proportional to the frequency of light emitted