Emission Spectrum Animation

Light and Energy• Particles (photons) and waves at the same time!

c = f • The greater f (frequency), the smaller

(wavelength)• The greater f, the higher the energy of the EM

radiation.

Energy = hf h is Plank’s Constant = 6.6262x10-34Js

Light and Energy

The electromagnetic spectrum

Energy and Frequency

• The higher the frequency, the greater the energy

Which has higher energy – red or blue light?

• Emission spectra known for hundreds of years

• Niels Bohr suggests a reason – energy levels

• Electrons orbiting in shells around the nucleus

• Energy levels differ from one another

Electrons and Light

• When an atom absorbs energy, electrons are promoted to higher energy levels.

• When the atom releases the absorbed energy, the electron falls back down to lower energy levels and EM radiation is given off (sometimes light)

“Too many photons for love, too much electromagnetic radiation…”

© Copyright Michael Offutt 1988http://bisontech.gfps.k12.mt.us/gfhs/teachers/jan_mader/Songbook.htm

Too Many Photons for Love

I went to a dance and saw her standing in the light. She was so beautiful, I knew I had to meet her. She had this look of intelligence and poise.

So, I figured out a novel way to greet her.

I just walked up and said…

There’s just too many photons for love.

Too much visible electromagnetic radiation.

Too many photons for love,

Too much subatomic excitation

I said now, so many people thought,

That light was just a wave.

And of course there were your usual particle fanatics.

But the way that light behaved made it clear to all

They did something more than classical mechanics.

So they figured out that maybe light was like a combo,

Bundles of energy that dance away the mambo.

But it’s almost midnight and this party’s getting stale.

Let’s find someplace dark,

And I’ll complete this quantum tale.

So we went to my place and sat and talked beside the fire,

About how atoms give off photons,

When electrons make transitions,

Jumping from high levels down to lower ones,

Resulting in colourful emissions.

And as the fire flickered low,

I kept on relating how the world was filled with atoms,

With electrons resonating.

Absorbing and emitting photons to disclose,

The beauty of a leaf, the colour of a rose.

There are only certain possibilities

• Electrons can only exist at discrete energy levels (these are called orbitals)

• Therefore, in changing levels, only certain amounts of energy can be released

• These amounts are unique to every element

Emission Spectra are Unique• http://jersey.uoregon.edu/vlab/elements/Elements.html

Visit the website and click on any element to see its unique emission and absorption spectra.

How are the lines of the line spectrum

formed?

n=1

n=2

n=3

n=4

Spectrum

UV

IR

Vi s ible

Ground State

Excited State

Excited StateExcited State unstable and drops back down

• Energy released as a photon• Frequency proportional

to energy drop

Excited State

But only as far as n = 2 this time

Summary• Electron normally in Ground State

• Energy supplied [ as heat or electricity]

• Electron jumps to higher energy level

• Now in Excited State

• Unstable

• Drops back to a lower level

• Energy that was absorbed to make the jump up is now released as a photon

• Frequency depends on difference in energy levels [ E2 - E1 = hf ] h is Plank’s Constant and f is frequency of light

• When electron falls to

n = 1 level gives UV Range

n = 2 level gives Visible Range

n = 3,4 or 5 levels gives IR Range