Waves, Particles, and the Spectrum

Quantum Theory

Learning Objectives

• TLW understand the electromagnetic spectrum and the mathematical relationships between energy, frequency, and wavelength of light (TEKS 6.B)

• TLW calculate wavelength, frequency, and energy of light using Planck’s constant and the speed of light (TEKS 6.C)

Engagement Activities

• Cool Cosmos Website

I. Intro

A. Model of an atom

1. Knowing there are positive (protons) and negative (electrons) particles

a) and opposite charges attract

b) why aren’t electrons “drawn” into the positive nucleus?

2. Scientists answered that question by

a) studying the emission and absorption of light by matter

b) there was a definite relationship between light and an atom’s electrons

3. The study of the behavior of light led to energy, matter and atomic structure

How it Started

Discovery Education web videos– link

Classical Gas: Classical and Quantum Physics

Particles Waving – The Dual Nature of Light and Matter

II. Waves and particles

A. Waves

1. It was believed light behaved as a wave (until the 1900’s)

2. Visible light is a kind of electromagnetic (em) radiation

=

energy that travels through space

also includes x-rays, microwaves, radio waves, ultraviolet and infrared light

3. Together ALL electromagnetic radiation form the electromagnetic spectrum

4. the properties of a wave give waves their repetitive naturea) Wavelength () - length of one

complete waveb) Frequency () - # of waves that

pass a point during a certain time period

measured in hertz (Hz) = 1/s

c) Amplitude (A) - distance from the origin to the trough/crest

amplitude

amplitude

crest

trough

Wave height

Longer wavelength

Shorter frequency

Greater frequency

Shorter wavelength

5. Frequency and wavelength are inversely proportional a)

b) c = speed of light (3.00 X 108

m/s)λ = wavelength (m, cm, nm)v = frequency (Hz)

c =

6. Knowing that all electromagnetic radiation travels in waves with each one having a different

wavelength and frequency

you can determine which type of em radiation there is

GIVEN:

= ?

= 434 nm = 4.34 10-7 m

c = 3.00 108 m/s

WORK: = c/

= 3.00 108 m/s 4.34 10-7 m

= 6.91 1014 Hz

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

B. Particles of light1. Two experiments led scientists to realize light not only acted as a wave but also as “particles”2. The photoelectric effect is the emissions from metals when light shines on metal

3. Basically, light knocked electrons off the metal and created an electrical current

3. BUT

the light had to be of a certain frequency for the photoelectric effect to take place

• Discovery Education web video –

Max Planck and Black Body Radiation - link

4. Max Planck studied the emission of light by hot objects in the 1900’s

a) hot objects don’t emit em energy continuously, like in a wave

b) instead, em energy is emitted in small, specific amounts called quanta

c) quantum = the minimum quantity of energy that can be lost or gained by an atom

d) giving us quantum theory

Classical Theory = Waves Quantum Theory

5. The energy of the photon is proportional to its frequency

a)

b) E = energy (J, Joules)h = Planck’s constant

(6.6262 10-34 J·s)v = frequency (Hz) of radiation

emitted

E = h

C. Quantum Theory

1. Albert Einstein (1905)

a) He concluded that light has the properties of both

waves and particles

b) wave-particle duality

c) a photon – a particle of electromagnetic radiation

The Spectrum

A. Line-Emission Spectrum

ground state

excited state

ENERGY IN PHOTON OUT

This element gives

435nm,

485nm,

655nm

This is the “fingerprint” for hydrogen

B. Can electrons have a wave-particle duality?

1. Louis de Broglie in 1924 asked if electrons could have a wave-particle nature.

2. Knew waves confined to a certain space had a certain frequency

3. So, electrons are confined to a certain space, should mean have a certain frequency

4. de Broglies lent support to the quantum model of the atom

5. Proof:

VISIBLE LIGHT ELECTRONS

6. The quantum model of an atom

2. Photons

a) have zero mass

b) carry a quantum of energy

c) the energy of a particular photon depends on the frequency of the em radiation

D. Conclusion

1. Electrons can only exist at certain, specific distances from the nucleus

2. Orbitals for atomic electrons vary in shape

3. Electrons move very quickly

4. Electrons give off em radiation

Group & Independent Practice

• Lab #20 – Flame Test (link) or see Addison-Wesley lab manual pages 151 - 154

• Calculating wavelength, frequency, and energy of light – link

• Chemistry Textbook (read pages 372 – 383)– Page 375, Problems 11 & 12– Page 379, Problems 13 & 14– Page 383, Problems 15 - 19

More Cool Stuff

DiscoveryEducation resources link