Development of Bohr's model of the atom

#### Introduction

**Niels Bohr**(1885-1962) was a Danish scientist who also worked with Thomson.- FUN FACT: And like always with physicists, they didn't get along.

- He later then went to work with Rutherford.
- One of his major contributions to Physics was predicting that
**Hydrogen**had only one electron, which was thought to be impossible.

#### Upgrading the Rutherford model

- Bohr attempted to apply
**quantum physics**to the Rutherford model of the atom to improve it.- Note that this was something new at the time, coming from Planck and Einstein

- Bohr realised that the "atomic oscillators" mentioned in Planck's postulates were probably
**electrons** - Bohr also observed that atoms produced
**radiation**that formed a characteristic**spectrum**for each element.- This was observed in the Hydrogen discharge tube experiment
- This is because when electrons become
**excited,**they move to a**higher energy state**(explained later). - But in these states, they are
**unstable.**So they**lose the excess energy**as photons or**EM Radiation**

- At first, Bohr attempted to apply the quantum ideas of Planck to the atom, but failed.

#### The Balmer Series

- In 1913, Bohr was introduced to
**Johann Balmer's**work on**Hydrogen spectra lines.** - Angstrom, another scientist, was able to
**measure the wavelengths**of the 4 most easily visible spectra lines of Hydrogen. - From that, Balmer formed a
**purely empirical and mathematical formula**that could**determine the wavelengths**of the spectra lines:

\begin{align} \lambda = b \times \frac{n^2}{n^2 - 2^2} \end{align}

- Where:
- $\lambda$ is the
**wavelength**of the spectra line (m) - $b$ is the
**Balmer constant**, which was found to be $3.6456\times 10^{-7}m$ - $n$ is an
**integer,**which was found to be 3, 4, 5 or 6.

- $\lambda$ is the
- It should be noted that, Balmer
**did not know the meaning behind it**and it was merely a formula which resulted from trying random numbers until they worked. - Jannes Rydberg, a scientist trying to find his own equation for spectral lines, altered Balmer's equation to fit
**Hydrogen-like atoms**.

\begin{align} \frac{1}{\lambda} = R_h [Z^2] \bigg(\frac{1}{{n_f}^2} - \frac{1}{{n_i}^2}\bigg) \end{align}

- Where
- $\lambda$ is the
**wavelength**of the spectra line (m) - $R_h$ is
**Rydberg's constant**($1.097 \times 10^7$) - $n_f$ and $n_i$ are integers.
- ($Z$ is the
**atomic number**of the element.**This is not required by the HSC**)

- $\lambda$ is the
- After Bohr saw these equations, he
**realised how electrons were arranged in the hydrogen atom**and how**quantum ideas**could be introduced to the atom. **ANALYSIS:**Thus, the Hydrogen spectrum was**pivotal**in the development of Bohr's model of the atom, allowing him to incorporate his quantum ideas (covered later) into his model of the atom.

page revision: 1, last edited: 04 Jul 2011 10:33