LIGHT and QUANTIZED ENERGY

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LIGHT and QUANTIZED ENERGY. Much of our understanding of the electronic structure of atoms has come from studying how substances absorb or emit light. To understand electric structure, therefore, we must first understand light. Visible light is only one type of

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LIGHT

and

QUANTIZED ENERGY

Much of our understanding of the electronic structure

of atoms has come from studying

how substances absorb or emit light.

To understand electric structure, therefore,

we must first understand light.

Visible light is only one type of

There are many different types

Gamma rays are emitted from the

nucleus of some radioactive atoms.

The electromagnetic spectrum contains

all the different types of electromagnetic radiation.

The different types of electromagnetic radiation

have different wavelengths and frequencies.

Wavelength

The distance between two adjacent crests (or troughs)

is called the wavelength.

crest

trough

The unit for wavelength is meters, m.

The electromagnetic spectrum is arranged

in order of increasing wavelength.

The wavelengths of gamma rays are as short

as the diameters of atomic nuclei.

Frequency

The number of wavelengths that pass a given point

each second is the frequency of the wave.

(1 wave/s)

(1.5 wave/s)

(3 wave/s)

What is the frequency of each wave?

time(sec)

3/s

Frequency =

?

1

2

1/s

Frequency =

?

time(sec)

1

2

Frequency is expressed in waves per second,

denoted /s or s-1.

Frequency is also expressed in hertz, Hz.

= 619 s-1

619 Hertz =

619 waves/sec

= 619/s

(1 wave/s)

(1.5 wave/s)

(3 wave/s)

Long wavelength

Low frequency

Short wavelength

High frequency

decreases

As the wavelength increases, the frequency ____________.

increases

As the wavelength decreases, the frequency ___________.

All types of electromagnetic radiation

move through a vacuum at a speed of

3.00 x 108 m/s, the speed of light.

As a result, the wavelength and frequency

of electromagnetic radiation are related by:

Speed of light

Wavelength (lambda)

c = νλ

Frequency (nu)

c = νλ

We can rearrange the equation to solve for

the frequency or the wavelength.

c

c

ν =

λ

=

ν

λ

c

c

ν =

λ

=

ν

λ

The wavelength and the frequency

are inversely related.

As one increases the other decreases.

As one decreases the other increases.

c = νλ

We can rearrange the equation to solve for

the frequency or the wavelength.

Calculate the wavelength of the yellow light

emitted by a sodium lamp if the frequency

of the radiation is 5.09 x 1014 Hz (5.09 x 1014/s).

Given:

Equation:

ν = 5.09 x 1014 /s

c

λ

=

c = 3.00 x 108 m/s

ν

λ = ?

What is the frequency of radiation with a

wavelength of 5.00 x 10-8 m?

Equation:

Given:

λ = 5.00 x 10-8 m

c

=

ν

c = 3.00 x 108 m/s

λ

ν = ?

The Particle Nature of Light

Thus far, we have learned that light and other radiation

behave like waves.

But light and other radiation also behave as if

composed of particles or rather packets of energy.

Energy is not absorbed

in a continues fashion.

Energy is absorbed

in small specific amounts,

in packets called quantum.

continues

stepwise

Energy is absorbed

in small specific amounts,

in packets called quantum.

Energy is not absorbed

in a continues fashion.

continues

stepwise

particle-like

wavelike

Matter can gain or lose energy only in small,

specific amounts called quanta (quantum).

That is, a quantum is the minimum amount of energy

that can be gained or lost by an atom.

Radiant energy is quantized.

A Photon

Electromagnetic radiation has both wavelike and particlelike characteristics.

Electromagnetic radiation can be thought of as

a stream of tiny particles, or bundles of energy,

called photons.

photon

Aphoton is quantum of radiant energy.

Energy of a photon = hν

Planck’s constant

Ephoton = hν

Unit for energy

is the joule, J.

Frequency

.

where h = 6.626 x 10-34 J s

The energy of a photon of light depends on the frequency,

the greater the frequency the greater the energy.

Ephoton = hν

Which electromagnetic radiation carries the most energy?

Lower frequency

less energy

Higher frequency

More energy

As the frequency increases

The energy increases

Gamma rays have the highest frequency of all radiation,

as a result gamma rays have the greatest energy .

Tiny water droplets in the air disperse the white light

of the sun into a rainbow. What is the energy of a photon

from the violet portion of the rainbow if it has a

frequency of 7.23 x 1014 s-1?

Equation:

Given:

ν = 7.23 x 1014 /s

E = hν

.

h = 6.626 x 10-34 J s

E = ?

A photon strikes an atom.

If the photon contains enough energy,

the electron will jump to a higher energy orbital.

Excited electron

If the photon doesn’t contain enough energy,

the electron will remain in the ground state.

E = hν

If the ∆E is large,

the energy emitted will

have a _____ frequency

and a ________ wavelength.

∆E = ?

is large

high

short

∆E = ?

If the ∆E is small,

the energy emitted will

have a _____ frequency

and a ________ wavelength.

is small

low

long

∆E = Ehigher energy orbit – Elower energy orbit

Change in energy

Each compound tested will produce a different color flame.

Flame colors are produced from the movement of the electrons

in the metal atoms present in these compounds.

For example, a sodium atom in its ground state has the electronic configuration 1s22s22p6.

When you heat the sodium atoms, the electrons gain energy and

can jump into any of the empty orbitals at higher levels - for example, into the 7s or 6p or 4d.

Because the electrons are now at a higher and more energetically unstable level,

they tend to fall back down to the ground state.

As they return to the ground state, they emit photons of a specific energy.

This energy corresponds to a particular wavelength of light,

and so produces particular colors of light. Each metal has a unique electron configuration.

The exact sizes of the possible jumps in energy terms vary from one metal to another.

That means that each different metal will produce a different flame color.

As electrons return to the ground state, they emit a certain frequency of radiant energy.

Ephoton = hν

Lower energy

higher energy