1. CHAPTER 5
The Structure
of the Atom
5.4 Light and Spectroscopy

2. 460 – 370 BC 1808 1870 1897 1910 1925 Today Democritus Atomism Dalton
“Modern”
atomic theory
Crookes
Cathode rays
Thomson
Discovery
of the electron
Rutherford
Discovery
of the nucleus
Pauli
Pauli exclusion principle

3. 460 – 370 BC 1808 1870 1897 1910 1925 Today Crookes Cathode rays
Democritus
Atomism
Dalton
“Modern”
atomic theory
Crookes
Cathode rays
Thomson
Discovery
of the electron
Rutherford
Discovery
of the nucleus
Pauli
Pauli exclusion principle

4. Pauli exclusion principle
460 – 370 BC
1808
1870
1897
1910
1925
Today
Democritus
Atomism
Dalton
“Modern”
atomic theory
Crookes
Cathode rays
Thomson
Discovery
of the electron
Rutherford
Discovery
of the nucleus
Pauli
Pauli exclusion principle

5. Do we have evidence to support these claims?
460 – 370 BC
1808
1870
1897
1910
1925
Today
Democritus
Atomism
Dalton
“Modern”
atomic theory
Crookes
Cathode rays
Thomson
Discovery
of the electron
Rutherford
Discovery
of the nucleus
Pauli
Pauli exclusion principle
Do we have evidence to support these claims?

6. Light is a form of electromagnetic energy that comes from electrons in atoms
The human eye can only detect a certain range of that energy: the visible spectrum.

7. Light is a form of electromagnetic energy that comes from electrons in atoms
The human eye can only detect a certain range of that energy: the visible spectrum.

8. White light from a lamp or the sun is not truly white!
Analyzing starlight with a prism
(one of the first spectrometers)
White light from a lamp or the sun is not truly white!

9. Visible light is only a small range in the electromagnetic spectrum

10. We are surrounded by electromagnetic energy

11. 1 electron volt (eV) = 1.602 x 10–19 J.
Energy of a photon
Remember that light travels as bundles called photons
A very small unit of energy
1 electron volt (eV) = x 10–19 J.

12. Wavelength and frequency are related

13. The wavelength of red laser light is 652 nm.
What is its frequency?
How much energy does a photon of this light have in electron volts?

14. The wavelength of red laser light is 652 nm. What is its frequency?
How much energy does a photon of this light have in electron volts?
Asked: Frequency and energy
Given:
Relationships:

15. The wavelength of red laser light is 652 nm. What is its frequency?
How much energy does a photon of this light have in electron volts?
Asked: Frequency and energy
Given:
Relationships:
Solve:

16. The wavelength of red laser light is 652 nm. What is its frequency?
How much energy does a photon of this light have in electron volts?
Asked: Frequency and energy
Given:
Relationships:
Solve:

17. The wavelength of red laser light is 652 nm. What is its frequency?
How much energy does a photon of this light have in electron volts?
Asked: Frequency and energy
Given:
Relationships:
Solve:
Answer: Since 1 Hz = 1/s, the frequency is 4.6 x 1014 Hz and the energy is 1.9 eV.

18. Light from an incandescent light bulb:
prism
all possible energy levels
electron

19. Light from pure hydrogen:
prism
fixed energy levels
electron

20. Hydrogen atoms can only absorb and emit light of very specific energies.

21. Why does the atom absorb only specific (discrete) energies?
Matter and light
Why does the atom absorb only specific (discrete) energies?

22. Matter and light
Why does the atom absorb only specific (discrete) energies?
Remember:
only some energy levels are allowed.

23. Energy (light) passes through the atom. Energy (light) is absorbed.
Matter and light
Energy levels
Energy levels
Photon
(energy)
Energy of the photon matches a gap between levels
Energy of the photon does not match a gap between levels
Energy (light) passes through the atom.
Energy (light) is absorbed.

24. Energy (light) is absorbed.
Matter and light
Energy levels
Photon
(energy)
another photon is emitted
Energy of the photon matches a gap between levels
specific color
(wavelength)
Energy (light) is absorbed.

25. Each type of atom has a different electron structure.
Each element has unique energy levels like a fingerprint.

26. Spectrum cards
How to read the spectrum cards

27. Combinations of elements contain spectral lines from both.
Spectrum cards
Combinations of elements contain spectral lines from both.

28. Energy of the photon matches a gap between levels
Reemission of light has two steps:
Energy levels
Photon
(energy)
Photon absorbed
Photon emitted
Energy of the photon matches a gap between levels

29. Emission spectrum Absorption spectrum
Range of energies
Emission spectrum
Energy levels
Photon
(energy)
Absorption spectrum

30. Visible light is only a small range of the electromagnetic spectrum.

31. Each type of atom has a different electron structure.
Each element has unique energy levels like a fingerprint.