Emission Spectrum Animation

Light and Energy• The electromagnetic spectrum • 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

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)

There are only certain posibilities

• Electrons can only exist at discrete energy levels

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

• These amounts are unique to every element

A Demo• http://www.visionlearning.com/library/flash_viewer.php?oid=1347&mid=51 • http://jersey.uoregon.edu/vlab/elements/Elements.html

• http://www.youtube.com/watch?v=QI50GBUJ48s

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