1. UNRAVELLING THE MYSTERIES OF THE ATOM AND THE UNIVERSE
Atomic Spectra
UNRAVELLING THE
MYSTERIES OF THE ATOM
AND THE UNIVERSE
R. Mulenga AS PHYSICS 2007

2. Thanks to John Parkinson
R. Mulenga
AS PHYSICS

3. A hot gas emits discrete line spectra
The spectrum of incandescent (very hot) solids is said to be continuous because all wavelengths are present
A continuous spectrum passing through a gas will have discrete line spectra removed
Diffraction grating
i.e. the sun, light bulb
eg Na, sodium metal flame test
A hot gas emits discrete line spectra

4. Absorption & Emission Spectra

5. Hydrogen Absorbtion Spectrum
Hydrogen Emission Spectrum
400 nm
500 nm
600 nm
700 nm

6. Flame Test
A flame test is used to visually determine the identity of an unknown metal in a compound
Elements heated by a flame will glow their characteristic color

7. Burning Elements (metals)
Calcium, Lithium, Rubidium, Sodium, Potassium

8. Spectroscope ~an instrument used to observe the colour components of any light source
When an element is burned and the flame looked at with a spectroscope, the color is revealed to consist of a pattern of distinct frequencies (eg like snowflakes, finger prints)

9. Bromine Deuterium Helium Hydrogen Krypton Mercury Neon Water Vapor
Xenon
Image and text copyright © Ted Kinsman.

11. Sun’s Spectrum

12. Halfway - Summary
The patterns lines are unique to each element and can be used to identify which elements are in the gas.
Line spectra are also called atomic spectra because the lines represent wavelengths (Photons?) radiated from atoms when electrons change from one energy level to another.

13. It was noticed that an atom can only absorb certain energies (colours) of light (the absorption spectrum) and once excited can only release certain energies (the emission spectrum) and these energies happen to be the same. 
The emission & absorption of light was connected with the behavior of electrons in the atom.

14. Balmer, despite being a mathematician, he is not remembered for any work in that field; rather, his major contribution was an empirical formula for the visible spectral lines of the hydrogen atom…
Balmer

15. Balmer constructed an empirical (invented to fit results) formula to describe the spectral lines in the Hydrogen spectrum.
Lines n=3, 4, 5, 6 were from the visible light spectrum
Other scientists discovered similar series of lines in the infrared and ultraviolet parts of the spectrum
n=6
n=5
n=4
n=3
for n=3, 4, 5,...
R = x 107 m-1

16. Lyman series (UV) Balmer series (visible light) Paschan series (IR)
Brackett series
for n = 2, 3, 4, ...
for n = 3, 4, 5, ...
for n = 4, 5, 6, ...
for n = 5, 6, 7, ...

17. Key understanding idea ~ there exists only exact steps / jumps
The number n, was later found (Bohr Model) to represent the shell or energy level that an electron resides in… ?????
Emission of light…
an electron jumps down a shell level (to a more stable level) and in the process emits a photon of light with λ…
Key understanding idea ~ there exists only exact steps / jumps

18. Key understanding idea ~ there exists only exact steps / jumps
Quantum…

20. The Hydrogen Spectrum
A formula was worked out to calculate the wavelengths of these lines:
R=Rydberg’s Constant =1.097x107 m-1 S=Series no. (the shell jumped into)
L=Line no. (the shell jumped from)

21. Balmer
Bohr

22. Quick verbal recap Concentrate and answer these Making an educated guess is better than “ I dunno”
So what is an atomic absorption spectra?
And an emission spectra?
They are useful because……………………………