Bohr's explanation of the Balmer Series

Introduction

  • Recall from before that the wavelengths of Balmer series can be found by:
(1)
\begin{align} \frac{1}{\lambda} = R_h [Z^2] \bigg(\frac{1}{{n_f}^2} - \frac{1}{{n_i}^2}\bigg) \end{align}
  • Bohr explained this mathematical equation in terms of his model of the atom:
    • Bohr thought that the equations described the wavelengths of the photons emitted when making the transition from excited states to lower states.
    • He thought that $n_i$ described the higher state of the electron and $n_f$ described the lower state that it travelled to.
  • This was reinforced by the Infra-red spectrum of the Paschen series, which supported the equation. (n = 3)
  • Later, more series' were found, these include:
    • The Lyman Series, which were Ultraviolet lines to the Ground state (n = 1) found in 1916
    • The Brackett series, which were Infra-red lines to the 3rd excited state (n = 4) found in 1922
    • The Pfund series, which were Infra-red lines to the 4th excited state (n = 5) found in 1924

Diagrammatical information.

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Important!

  • You will need to be able to draw the circle on the right. Knowing the left side doesn't hurt.
  • While the diagram shows other wise, you must realise that the lines get closer as n gets larger.