• Anyone who is not shocked by quantum mechanics has not understood it.

—Neils Bohr (1885–1962)

December 3

• Objectives:• View emission spectrum of Hydrogen, identify

the color bands• Understand Bohr’s model of the atom

Observations

• Look at the light produced by the hydrogen lamp

• What color is it?• Put on your diffraction glasses • What colors can you see now?

This means hydrogen is producing specific bands of light with definite wavelengths/frequencies.

Hydrogen Emission Spectrum:• Pink light emitted from hydrogen• When separated by a prism, shows

distinct bands of color

Niels BohrNobel Prize – 1922• “For his services in the investigation

of the structure of atoms and the radiation emanating from them”

• Five facts from the next four slides…

Niels Bohr’s Atom (Slide 1 of 3)

•Electrons move around the nucleus in orbits, like a solar system. The orbits are sometimes called energy levels.

Planetary Model

Electrons cannot exist between orbits (energy is quantized)

(Slide 1b of 3)

Electrons cannot exist between orbits – think of rungs on a ladder. You can’t be in between one rung and another.

Bohr’s Atom (Slide 2 of 3)

• Electrons closest to the nucleus are lowest in energy.

• Electrons farthest from the nucleus are highest in energy.

• Ground state- electrons are in the lowest energy level possible

• Excited state - If energy is put into the atom, the electrons will jump up in energy (move away from the nucleus)

Bohr’s Atom (Slide 3 of 3)

• Excited electrons naturally go back to ground state. In order to do this, energy must leave the atom. Because energy is quantized in an atom, the amount of energy that leaves is the difference in energy between orbits.

• If this energy is in the visible light range, we will see certain colors

Atomic Spectra• Absorption: When energy is added and an electron

moves from a lower energy level to a higher energy level

• Emission: When an electron falls from a higher energy level to a lower energy level and a photon is emitted.

The energy of each absorbed or emitted photon corresponds to a particular frequency, E = hν

Hydrogen Atom Line Emission Spectrum

Ground State: Lowest energyExcited State: Higher energy

When an electron “falls” from higher to lower energy, it gives off extra energy (E) as a photon (E=hν)

This produces bandsof light with definite wavelengths.

Electron transitionsinvolve jumps of definite amounts ofenergy.

Hydrogen Emission Spectrum:• Pink light emitted from hydrogen• When separated by a prism, shows

distinct bands of color

Electron at highest energy level produces what kind of EMR? - UV

The electron at lowest energy level? - Red

IMPLICATIONS

Classical Theory: (old)• Any amount of energy could be absorbed or

emitted

Quantum Theory: (new)• Hydrogen atoms can only have EXACT energy

levels

One More Thing in the Notes

• Summary: Write a 1-2 sentence summary of the Bohr model of the atom and the hydrogen emission spectrum.

Flame Tests

strontium sodium lithium potassium copper

Many elements give off characteristic light which can be used to help identify them.

Next time - Thursday

• Flame Test Lab• You will determine the emission spectra of a

number of elements using colored flames• Close-toed shoes• Ladies: Something to tie your hair back