Formation of Light

Nucleus

e e

e

Lithium Atom

+

Ground State

e e e e e e

e

Excited State

e

Electron Returns to Ground State

Light is given offe

Ion is formedLi e + Li1+

hv

n = 1

n = 2

n = 3

n = 4

n = 5

n = 6

n = 7

Nucleus Nucleus Nucleus

Waves

• Wavelength () - length of one complete wave

• Frequency () - # of waves that pass a point during a certain time period– hertz (Hz) = 1/s

• Amplitude (A) - distance from the origin to the trough or crest

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

f

The Electromagnetic Spectrum

AM radio

Short waveradio

Television channels

FM radio

RadarMicrowave

Radio Waves Gamma Rays

X- Raysinfrared

Increasing photon energy

Increasing frequency

Decreasing wavelength

Red Orange Yellow Green Blue Indigo Violet

UV Rays

Visible

Light

R O Y G B I V

HIGH

ENERGY

LOW

ENERGY

Frequency

O’Connor, Davis, MacNab, McClellan, CHEMISTRY Experiments and Principles 1982, page 166

1 second

Frequency

4 cycles/second = 4 hertz

12 cycles/second = 12 hertz

36 cycles/second = 36 hertz

AM & FM WavesCarrier frequency

Sound pattern

Amplitude Modulated carrier

Frequency Modulated carrier

AM - FM Radio

Electromagnetic Spectrum

LOW

ENERGY

HIGH

ENERGY

g rays X-rays Ultraviolet Infrared Microwave

Radar

Radio waves

TVFM

ShortWave

LongWave

Visible spectrum

10-2nm 10-1nm 100nm 101nm 102nm 10-3cm 10-2cm 10-1cm 100cm 101cm 1cm 101m 102m 103m 104m

1019Hz 1018Hz 1017Hz 1016Hz 1014Hz 1013Hz 1012Hz 1011Hz 1010Hz 109Hz 100 MHz 10 MHz 1 MHz 100 KHz

RedOrangeYellowViolet Blue Green

700 nm600 nm500 nm400 nm

Wavelength, l

Frequency, n

103nm

1015Hz

Electromagnetic spectrum

WhiteLight

Davis, Frey, Sarquis, Sarquis, Modern Chemistry 2006, page 98

Waves

Low frequency

High frequency

Amplitude

Amplitude

long wavelength l

short wavelength l

Waves

Low frequency

High frequency

Amplitude

Amplitude

long wavelength l

short wavelength l

60 photons

162 photons

low energy

high energy

Electromagnetic Radiation

Light as a wave

Light as a stream of energy

(packets of photons)Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 325

Wavelength and Frequency

E = h n

c = n l c = speed of light (3 x 108 m/s)n = frequency (s-1) l = wavelength (m)

E = energy (Joules or J)h = Planck’s constant (6.6 x10-34 J/s)n = frequency (s-1)

f f

ff

ch

E

“nu” “lambda”

c f

Electromagnetic Spectrum

GIVEN:

f = ?

= 434 nm

= 4.34 10-7 m

c = 3.00 108 m/s

WORK:

f = 3.00 108 m/s 4.34 10-7 m

f = 6.91 1014 Hz

• EX: Find the frequency of a photon with a wavelength of 434 nm.

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

f c

1 x 109 nm

1 m

Coins are Quantified

Do we have a coin for 37cents?

Light is also quantified and only comes in certain bundles called photons.

Bohr Model of Hydrogen

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 331

Nucleus

Possible electron orbits

e

e

Continuous vs. Quantized Energy

Ene

rgy

A BZumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 330

continuous quantized

Continuous vs. Quantized

A BZumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 330

Wavelength and Frequency

E = h n

c = n l c = speed of light (3 x 108 m/s)n = frequency (s-1) l = wavelength (m)

E = energy (Joules or J)h = Planck’s constant (6.6 x10-34 J/s)n = frequency (s-1)

f f

ff

ch

E

“nu” “lambda”

Photoelectric Effect

No electrons are emitted Electrons are emitted

Metal plate Metal plate

Bright red light

infrared rays

or

Dimblue light

ultraviolet rays

or

Intensity of Radiation

1x 2x 3x

¼ light 1/9 light

Light intensity = 1/(distance)2

The Photoelectric Effect

When light strikes a metal surface,electrons are ejected.

If the threshold frequency has beenreached, increasing the intensity onlyincreases the number of electrons ejected.

If the frequency is increased, theEjected electrons will travel faster.

A B C

Light

Electron

MetalNucleus

More Light

Electron

MetalNucleus

Electron

HigherfrequencylightFaster

electron

MetalNucleus

Photoelectric Effect

Some key results

For low frequency light (low energy, below threshold) - electrons are not ejected regardless of the light’s intensity (number of light waves)

For high frequency light (high energy, above threshold) - same number of electrons are ejected regardless of the frequency (energy of light waves)

- Increasing the light’s intensity increases the number of electrons ejected (increases the current)

Einstein considered light as mass-less, energetic particles (photons)to help explain this effect – energy follows Planck’s equation.

Photoelectric Generator

Solar Calculator

The Photoelectric effect and the frequency of light

IR, infraredRedOrangeYellowGreenBlueVioletUV, ultraviolet

UV v b g y o r IR

Lens

Slit

Quartz prism

Light source

Hill, Petrucci, General Chemistry An Integrated Approach 1999, page 292

Potassium

Quantum Theory

E: energy (J, joules)h: Planck’s constant (6.6262 10-34 J·s): frequency (Hz)

E = h

• The energy of a photon is proportional to its frequency.

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Quantum Theory

GIVEN:

E = ? = 4.57 1014 Hzh = 6.6262 10-34 J· s

WORK:

E = h

E = (6.6262 10-34 J· s) (4.57 1014 Hz)

E = 3.03 10-19 J

• Example: Find the energy of a red photon with a frequency of 4.57 1014 Hz.

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Color = Energy of Photons

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 329

Energy Level

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 329

A

B

C

D

Ground state

En

erg

y

Fourexcitedstates

An Excited Lithium Atom

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 326

Photon ofred lightemitted

Li atom inlower energy state

Excited Li atom

Ene

rgy

Frequency A

Frequency B

Frequency C

n = 2

n = 1

n = 3

A

B

C

A + B = C

Bohr’s Experiment

Kelter, Carr, Scott, Chemistry A Wolrd of Choices 1999, page 76 Animation by Raymond Chang – All rights reserved.

Hydrogen Spectral Lines

Lyman series(ultraviolet)

Balmer series(visible)

Paschen series(infrared)

Frequency(hertz)

1016 1015 1014

7 6 5 4 3 2 1 n =

Hydrogen Spectral Lines

A B C D E F

Lyman series (UV)

A B C D E

Balmer (Visible)

A B C D

Paschen (IR)

E1

E2

E3

E4

E5

E6

En

erg

y

Bohr’s model of the atom accounted mathematically for the energy of each of the transitions shown.

IRregion

UVregion

656 nm

486 nm

434 nm

410 nm

Davis, Metcalfe, Williams, Castka, Modern Chemistry, 1999, page 97

ionization

Continuous and Line Spectra

4000 Ao

5000 6000 7000

light

Na

H

Ca

Hg

400 450 500 550 600 650 700 750 nm

Visiblespectrum

l (nm)

Flame Emission Spectra

Photographs of flame tests of burning wooden splints soaked in different salts.

Include link to web page

http://www.unit5.org/christjs/flame%20tests.htm

methane gas wooden splint strontium ioncopper ionsodium ion calcium ion

The Electromagnetic Spectrum

AM radio

Short waveradio

Television channels

FM radio

RadarMicrowave

Radio Waves Gamma Rays

X- Raysinfrared

Increasing photon energy

Increasing frequency

Decreasing wavelength

Red Orange Yellow Green Blue Indigo Violet

UV Rays

R O Y G B I V

Visible

Light

1.5

1.2

0.9

0.6

0.3

0.0300 400 500 600 700 800

Wavelength (nm)

Abs

orb

ance

Absorbance of Chlorophyll

1026 1024 1022 1020 1018 1016 1014 1010 108 106 104 102 1

10-8 10-6 10-4 10-2 1 102 104 106 108 1010 1012 1014 1016

Frequency (Hz)

Wavelength (nm)

cosmicrays

gammarays

x-rays ultra-violet

infra-red

radio(microwave)

radar tele-vision

radio powertransmission

Violet Blue Green Yellow Orange RedUV

NearInfrared

400 nm 500 nm 600 nm 700 nm

Wave Interference

Wave Interference

Bright

Bright

Bright

Bright

Bright

Bright

Bright

A

B

C

D

Waves

crest

trough

wavelength

amplitude

E F G Hreflection refraction total internal reflection diffraction

crest

wavelength

amplitude

troughreflection

refractiondiffraction

total internal reflection(Match the terms…)

Polarizing Filter

Vertical polarizing filter

Horizontal polarizing filter

Vertical wavepasses through

Horizontal waveis blocked

side view

Vertical wave is blocked

by horizontal polarizing filter