CHAPTER 5

The Structure

of the Atom

5.4 Light and Spectroscopy

2 5.4 Light and Spectroscopy

Today1808 1870 1897 1910 1925

DemocritusAtomism

460 – 370 BC

Dalton“Modern”

atomic theory

CrookesCathode rays

ThomsonDiscovery

of the electron

RutherfordDiscovery of the nucleus

PauliPauli exclusion principle

3 5.4 Light and Spectroscopy

Today1808 1870 1897 1910 1925

DemocritusAtomism

460 – 370 BC

Dalton“Modern”

atomic theory

CrookesCathode rays

ThomsonDiscovery

of the electron

RutherfordDiscovery of the nucleus

PauliPauli exclusion principle

4 5.4 Light and Spectroscopy

Today1808 1870 1897 1910

DemocritusAtomism

460 – 370 BC

Dalton“Modern”

atomic theory

CrookesCathode rays

ThomsonDiscovery

of the electron

RutherfordDiscovery of the nucleus

1925

PauliPauli exclusion principle

5 5.4 Light and Spectroscopy

Today1808 1870 1897 1910

DemocritusAtomism

460 – 370 BC

Dalton“Modern”

atomic theory

CrookesCathode rays

ThomsonDiscovery

of the electron

RutherfordDiscovery of the nucleus

1925

PauliPauli exclusion principle

Do we have

evidence to

support these

claims?

6 5.4 Light and Spectroscopy

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 5.4 Light and Spectroscopy

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 5.4 Light and Spectroscopy

White light from a lamp or the sun is not truly white!

Analyzing starlight with a prism(one of the first spectrometers)

9 5.4 Light and Spectroscopy

Visible light is only a small range in the electromagnetic spectrum

10 5.4 Light and Spectroscopy

We are surrounded by electromagnetic energy

11 5.4 Light and Spectroscopy

Remember that light travels as bundles called photons

1 electron volt (eV) = 1.602 x 10–19 J.

A very small unit of energy

Energy of a photon

12 5.4 Light and Spectroscopy

Wavelength and frequency are related

13 5.4 Light and Spectroscopy

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 5.4 Light and Spectroscopy

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:

9652 10 m ,c E h

15 5.4 Light and Spectroscopy

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:

9652 10 m ,c E h

9

15 14

8 143 10 / 4.6 10

652 1

4.136 10 4.6 10 / 1.9

0

c m sc therefor

E h e

m

s

es

V s eV

16 5.4 Light and Spectroscopy

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:

9652 10 m ,c E h

9

15 14

8 143 10 / 4.6 10

652 1

4.136 10 4.6 10 / 1.9

0

c m sc therefor

E h e

m

s

es

es VV

17 5.4 Light and Spectroscopy

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.

9652 10 m ,c E h

8 14

9

15 14

3 10 / 4.6 10

652 10

4.136 10 4.6 10 .91 /

c m sc therefore

m

e

s

E h e VV s s

18 5.4 Light and Spectroscopy

prism

electron

all possible energy levels

Light from an incandescent light bulb:

19 5.4 Light and Spectroscopy

prism

electron

fixed energy levels

Light from pure hydrogen:

20 5.4 Light and Spectroscopy

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

21 5.4 Light and Spectroscopy

Why does the atom absorb only specific (discrete) energies?

Matter and light

22 5.4 Light and Spectroscopy

Remember: only some energy levels

are allowed.

Why does the atom absorb only specific (discrete) energies?

Matter and light

23 5.4 Light and Spectroscopy

Energy levels

Photon(energy)

Energy levels

Energy of the photon matches a gap between levels

Energy (light) is absorbed.

Energy of the photon does not match a gap between levels

Energy (light) passes through the atom.

Matter and light

24 5.4 Light and Spectroscopy

Energy levels

Photon(energy)

Energy of the photon matches a gap between levels

Energy (light) is absorbed.

another photon is emitted

specific color(wavelength)

Matter and light

25 5.4 Light and Spectroscopy

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

26 5.4 Light and Spectroscopy

Spectrum cards

How to read the

spectrum cards

27 5.4 Light and Spectroscopy

Combinations of elements contain spectral lines from both.

Spectrum cards

28 5.4 Light and Spectroscopy

Photon emitted

Photon absorbed

Energy levels

Photon(energy)

Energy of the photon matches a gap between levels

Reemission of light has two steps:

29 5.4 Light and Spectroscopy

Energy levels

Photon(energy)

Range of energiesEmission spectrum

Absorption spectrum

30 5.4 Light and Spectroscopy

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

31 5.4 Light and Spectroscopy

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