wavelength Visible light

wavelength

Ultraviolet radiation

Amplitude

Node

Chapter 6: Electromagnetic Radiation

Figure 7.1Figure 7.1

Long wavelength --> small frequency

low energy

Short wavelength --> high frequency

high energy

Which has the longest wavelength?

1 2 3 4

25% 25%25%25%1. Infrared

2. Ultraviolet

3. X-rays

4. Radio waves

Rank the following in order of increasing frequency:

 

microwaves

radiowaves

X-rays

blue light

red light

UV light

IR light

• Waves have a frequency• Use the Greek letter “nu”, , for frequency,

and units are “cycles per sec”• All radiation: • = c • c = velocity of light = 3.00 x 108 m/sec• Long wavelength --> small frequency• Short wavelength --> high frequency

What is the wavelength of WONY?

What is the wavelength of cell phone radiation? Frequency = 850 MHz

What is the wavelength of a microwave oven? Frequency = 2.45 GHz

Energy of radiation is proportional to frequencyEnergy of radiation is proportional to frequency

h = Planck’s constant = 6.6262 x 10h = Planck’s constant = 6.6262 x 10-34-34 J•s J•s

Light acts as if it consists of particles called PHOTONS, with discrete energy.

E = h •

Quantization of Energy

Relationships:

E = h •

Short wavelength light has:

1 2 3 4

25% 25%25%25%1. High frequency and low energy

2. High frequency and high energy

3. Low frequency and low energy

4. Low frequency and high energy

Rank the following in order of increasing photon energy: 

microwavesradiowavesX-raysblue lightred lightUV lightIR light

E = h •

What is the energy of a WONY photon?What is the energy of a WONY photon?

Energy of RadiationWhat is the frequency of UV light with a What is the frequency of UV light with a

wavelength of 230 nm?wavelength of 230 nm?

What is the energy of 1 photon of UV light What is the energy of 1 photon of UV light with wavelength = 230 nm?with wavelength = 230 nm?

What is the energy of a photon of 525 nm light?

1 2 3 4

25% 25%25%25%1. 3.79 x 10-19 J

2. 4.83 x 10-22 J

3. 3.67 x 1020 J

4. 8.43 x 1023 J

What is the energy of a mole of 230 nm photons?What is the energy of a mole of 230 nm photons?

Can this light break C-C bonds with an energy Can this light break C-C bonds with an energy of 346 kJ/mol?of 346 kJ/mol?

Does 1200 nm light have enough energy to Does 1200 nm light have enough energy to break C-C bonds?break C-C bonds?

Where does light come from?

• Excited solids emit a continuous spectrum of light

• Excited gas-phase atoms emit only specific wavelengths of light (“lines”)

Light emitted by solids

Light emitted by hydrogen gas

The Bohr Model of Hydrogen Atom

• Light absorbed or emitted is from electrons moving between energy levels

• Only certain energies are observed• Therefore, only certain energy levels exist

– This is the Quanitization of energy levels

• Excited atoms emit light of only certain wavelengths

• The wavelengths of emitted light depend on the element.

Emission spectra of gaseous atoms

Line spectra of atoms

Energy Absorption and Emissionsim

For H, the energy levels correspond to:

18

n 2

2.18 x 10 JE =

n

Energy level diagram:

Each line corresponds to a transition:

Example: n=3 n = 2

Balmer seriesBalmer series

Explanation of line spectra

Longest wavelength emission?

A. 1

B. 2

C. 3

D. 4

E. 5

1 2 3 4 5

20% 20% 20%20%20%

Longest wavelength absorption?

A. 1

B. 2

C. 3

D. 4

E. 5

1 2 3 4 5

20% 20% 20%20%20%

Lowest energy emission?

A. 1

B. 2

C. 3

D. 4

E. 5

1 2 3 4 5

20% 20% 20%20%20%

Lowest energy absorption?

A. 1

B. 2

C. 3

D. 4

E. 5

1 2 3 4 5

20% 20% 20%20%20%

Ionization?

A. 1

B. 2

C. 3

D. 4

E. 5

1 2 3 4 5

20% 20% 20%20%20%

Matter Waves

• All matter acts as particles and as waves.• Macroscopic objects have tiny waves- not

observed.• For electrons in atoms, wave properties are

important.

• deBroglie Equation: h

mv

Can see matter waves in experiments

Matter waves

Macroscopic object: 200 g rock travelling at 20 m/s has a wavelength:

Electron inside an atom, moving at 40% of the speed of light:

Heisenberg Uncertainty Principle

• Can’t know both the exact location and energy of a particle

• So, for electrons, we DO know the energy well, so we don’t know the location well

Schrodinger’s Model of H

• Electrons act as standing waves• Certain wave functions are “allowed”• Wave behavior is described by wave

functions: 2 describes the probability of finding the

electron in a certain spot– Also described as electron density

Hydrogen Wave Functions

Example Wavefunction

Equation slightly simplified:

o-r/a2 2 = x e g

Where is this function zero or near zero?

1 2 3

33% 33%33%1. When x = 0

2. When r = 0

3. When r is large

o-r/a2 2 = x e

It’s all about orbitals

• Each wavefunction describes a shape the electron can take, called an ORBITAL

• Allowed orbitals are organized by shells and subshells– Shells define size and energy (n = 1, 2, 3, …)– Subshells define shape (s, p, d, f, …)

• Number of orbitals is different for each subshell: s = 1 orbital

p = 3 orbitals d = 5 orbitals f = 7 orbitals

NODES

Spherical Nodes

Quantum Numbers and Numbers of Orbitals