8/12/2019 CHEM131_Lecture_2-4-14

1/16

Lecture February 4

1

Chapter 7: Quantum-

Mechanical Model of the Atom

Remember: No MC quiz due untilThursday Feb 13

8/12/2019 CHEM131_Lecture_2-4-14

2/16

Chapter 7

2

Light is the visible part of a largespectrum of electromagnetic radiation

It is a wave with an amplitude,

frequencyand wavelength

amplitude - how large or high the wave is

frequency !- how many waves pass a fixed

point in a secondwavelength "- the length between the pointswhere the wave repeats - e.g. peak to peak

8/12/2019 CHEM131_Lecture_2-4-14

3/16

Wavelength and Frequency

3

velocity of a wave (m/s) = !(s-1) "(m) = c

Light has a velocityc = 2.998 x 108m/s

OR

!= c/" "= c/!

c = !"

Really only one equation

8/12/2019 CHEM131_Lecture_2-4-14

4/16

Electromagnetic

Spectrum

4

See Fig. 7.5

8/12/2019 CHEM131_Lecture_2-4-14

5/16

Sample Calculations

5

WTOP is at a frequency of 103.5 MHzWhat is the corresponding wavelength?

"= c/!"= (2.998 x 108 m/s)/(103.5 x 106s-1)

= 2.897 m

What is the frequency of yellow light with awavelength of 600 nm (assume 3 sig fig)?

!= c/"= (2.998x108)/(600 x 10-9) =5.00 x 1014Hz

8/12/2019 CHEM131_Lecture_2-4-14

6/16

The Photon

6

Packet of light is also a particlecalled aphoton

Energy of a

photon of lightE = h!h = 6.626 x 10-34J-s

Plancks constant

OR E = hc/"!= c/"

8/12/2019 CHEM131_Lecture_2-4-14

7/16

Energy Calculations

7

What is the energy of 1 photon ofyellow light?

E = h!

= (6.626 x 10-34J-s) x (5.00 x 1014s-1)

=3.31 x 10-19J for a single photon

8/12/2019 CHEM131_Lecture_2-4-14

8/16

Remember the

ElectromagneticSpectrum

8

8/12/2019 CHEM131_Lecture_2-4-14

9/16

Emission and Absorption Spectra

9

#E negative =emission

#E positive =

absorption

nf= $

ionize the atom -complete removal of

the electron

schematic picture of theHydrogen atoms energy levels

8/12/2019 CHEM131_Lecture_2-4-14

10/16

Examples of

Emission Spectra

10

Sun

hydrogen

helium

mercury

uranium

8/12/2019 CHEM131_Lecture_2-4-14

11/16

WhirlpoolGalaxy

11

Hubble optical image

All images from

chandra.harvard.edu

8/12/2019 CHEM131_Lecture_2-4-14

12/16

Infrared Spectrum -Spitzer - stars and interstellar

12

In UltravioletGALEX - hot young stars

8/12/2019 CHEM131_Lecture_2-4-14

13/16

Chandrax-rayimage

13

Bright spots areblack holes and

neutron stars

8/12/2019 CHEM131_Lecture_2-4-14

14/16

14

Cassiopeia - Supernovae

Remnantdi%erent

colorsdenote

di%erentenergies ofEM radiation

Chandra X-ray image

8/12/2019 CHEM131_Lecture_2-4-14

15/16

Infrared

1512

Spitzer image

Optical Hubble

Image

blue = 3.6 &m, green = 4.5 &morange =5.8 &m, red = 8.0 &m

visible spectrum0.40 - 0.70 &m

(400 - 700 nm)

8/12/2019 CHEM131_Lecture_2-4-14

16/16

Quiz of the Day

16

What is the energy of an X-ray photon witha wavelength of 2.0 x 10-2nm?

Express your answer in 10-15J

Answer:

E = hc/"

= (6.626x10-34)(2.998x108)/(2.0x10-2x10-9)= 9.9 x 10-15J