Chapter 7: Quantum Theory and Atomic Structure

The Nature of Light

Atomic Spectra

The Wave - Particle Duality of Matter and Energy

The Quantum - Mechanical Model of the Atom

Chapter 7 - Quantum Theory of the Atom

Problems: 19, 23, 27, 31, 33, 37, 39, 43, 45, 47,

49, 51, 53, 57, 63, 65, 67, 71, 75, 77, 81,

Read the entire chapter

Answer all the Review Problems.

What are the electrons doing in the atom?

Why do atoms form ions and molecules?

Why do hydrogen and oxygen “stick” together to

form water?

To understand these questions, we need to understandthe electronic structure of the atom

Electronic structure referes to the way the electrons

are arranged in an atom

Atoms are the basic building blocks of matter.

They are the smallest units of an element that can

combine with other elements (that is, take part in

a chemical reaction.

Structure of the Atom

The simple view: only three subatomic particleshave a bearing on chemical behavior.

Protons, Neutrons and Electrons

Proton is a nuclear particle having a positive chargeequal to that of the electron and a mass more that 1800 times that of the electrons.

Neutron is a nuclear particle having a mass almost identical to that of the proton butwith no electric charge

Electron is a negatively charged particle withthe negative charge equal to that of the proton.

Protons and neutrons reside together in a very small volume within the atom known as the nucleus.

Most of the rest of the atom is space in whichthe electrons move

neutrons

protons

electrons

1. Each element is composed of extremely small particles called atoms.

2. All atoms of a given element are identical.

3. Atoms of different elements have different properties (including different masses).

4. Atoms and elements are not changed into differenttypes of atoms by chemical reactions.

5. Compounds are formed when atoms of morethan one element combine.

We Know:

Atoms (elements) are the basic unit of chemical stucture and are made of protons, neutronsand electrons (simplification)

Compounds are made up of elements (atoms) in difinite proportions. Compounds are also called Molecules.

6

C12.011

14A

2

Parts of the Periodic Table

Group

Per

iod

Atomic symbol

Atomic number

Atomic mass(amu)

The present theory of the electronic structure of the atom

started with an explanation of the colored light produced

in hot gases and flames

This means we need to know something about the natureof light and radiant energy

Radiant energy is electromagnetic radiation: light, X rays

All types of radiant energy move through a vacuum atthe speed of light (c) 3.00 x 108 m/s

All radiant energy has wavelike characteristics

A wave is periodic in nature and can be characterized

by its wavelength and frequency

is thedistance between any two adjacent identical points of a wave

Frequency (- the number of wavelengths of that wavethat pass a fixed point in one unit of time (usually 1 sec.)

Short wavelengthHigh Frequency

Long wavelengthlow frequency

Wavelength and frequency are related

What else do we know?

We said that all types of radiant energy move througha vacuum at 3.0 x 108 m/s

We know that is the distance between identical pointson successive waves

We know that is the number of times per second thatone complete wavelength passes a given point.

So:

c =

The yellow light given off by a sodium lamp has a wavelength of 589 nm. What is the frequency of this radiation?

c =

c/

c = 3.0 x 108 m/s

= 3.0 x 108 m/s

589 nm

x 109 nm

1 m= 5.09 x 1014/s

Electromagnetic radiation (light) consists of occilations

in electric and magnetic fields that can travel through

space. These occilations can be characterized in terms

of wavelength and frequency

The range of frequencies and wavelengths of

electromagnetic radiation is called the

electromagnetic spectrum

The visible spectrum 400 nm (violet) to 800 nm (red)

Fig. 7.3

The Spectrum of Electromagnetic Radiation

• The wavelength of visible light is between 400 and 700 nanometers

• Radio, TV , microwave and infrared radiation have longer wavelengths (shorter frequencies), and lower energies than visible light.

• Gamma rays and X-rays have shorter wavelengths (larger frequencies), and higher energies than visible light!

Fig. 7.1

Fig. 7.2

Electromagnetic Radiation

• WAVELENGTH - The distance between identical points on successive waves. ( )

• FREQUENCY - The number of waves that pass through a particular point per second. ()

• AMPLITUDE - The vertical distance from the midline to a peak, or trough in the wave.

c

Calculation of Frequency from Wavelength

Problem: The wavelength of an x-ray is 1.00 x10 -9 m or 1 nm, what is the frequency of this x-ray? If the wavelength of long-wavelength electromagnetic radiation is 7.65 x 104 m, what is the frequency of this long-wavelength radiation used to contact submerged nuclear submarines at sea?Plan: Use the relationship between wavelength and frequency to obtainthe answer. wavelength x frequency = speed of light!Solution:

frequency(cycles/sec) = speed of light wavelength(m)

frequency = = 3.00 x 1017 cycles/sec3.00 x 108 m/s1.00 x 10 - 9 m

a)

b) frequency = = 3.92 x 103 cycles/s 3.00 x 108 m/s7.65 x 104 m

Different Behaviors of Waves and Particles

Fig. 7.4

The Diffraction Pattern Caused by Light Passing through Two Adjacent Slits

Fig. 7.5

The Photoelectric Effect - I• Below the threshold energy,

nothing occurs !• Above the threshold, the

kinetic energy of the ejected electrons is proportional to the frequency of the light.

• Also, when above the threshold, as intensity of the light increases, so does the number of ejected electrons.

• All metals experience this effect, but each has a unique threshold frequency.

The Photoelectric Effect - II

• Albert Einstein

– Theorized Photons

– Won Nobel prize - 1921

• Photons have an energy equal to:

E = h• h = Plank’s Constant, and

is equal to:

6.6260755 x 10 - 3 4Jsec

Demonstration of the Photoelectric Effect

Fig. 7.7