Background

Electrons give off light when they return to the ground state after being excited by an energy source

Bohr studies the light given
off by a 'Black Body'

'Black Body' = heated body that gives off only the light from its internal glow - no reflected light

Material was heated and the light
given off was analyzed

Black Box
St. Mary's H.S. Physics Online

Atomic Spectra
(spectral lines)
St. Mary's H.S. Physics Online

Atomic Spectra
University of Oregon

Atomic Spectra for Iron

Full Spectrum

Hydrogen Emission
/Absorption Spectrum

Place your mouse over the image to see the absorption spectra

Full Spectrum

Helium Emission/Absorption
Spectrum

Place your mouse over the image to see the absorption spectra

Every Energy level transition creates
a single spectral line

Don Ion

How many different spectral lines can be produced
by an atom with 5 energy levels?

Answer

10 Spectral Lines

Black Body Radiation Results:

1. Only the high energy objects gave off colors on the violet side of the spectrum

2. Electrons in atoms are not capable of giving off all colors (energies)

3. Each element gives off a unique pattern of colors called a 'bright line spectrum'.

This knowledge is very useful to chemists and other scientists. Why?

Answer

1. Spectral lines used to:

To identify an unknown element

- Electrify, Heat it up and analyze its colors.

- Compare emitted colors to a database of elemental spectral lines

The diagram below represents the bright-line spectra of four elements, A, B, C, and D, and the spectrum of an unknown gaseous sample.

Based on comparisons of these spectra,
which two elements are found
in the unknown sample?

B and C