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

Thanks to John Parkinson R. Mulenga AS PHYSICS

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

Absorption & Emission Spectra

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

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

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

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)

Bromine Deuterium Helium Hydrogen Krypton Mercury Neon Water Vapor Xenon Image and text copyright © Ted Kinsman. http://www.astrographics.com/GalleryPrintsIndex/GP4259.html

Sun’s Spectrum

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.

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.

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

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 = 1.097 x 107 m-1

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, ...

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

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

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)

Balmer Bohr

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……………………………