Electromagnetic Radiation (EMR)
Electromagnetic radiation (EMR):
EM spectrum:
Parts of a wave:
Waves have 3 primary characteristics:
1.
2.
3.
The wavelength
(λ) and the frequency (ν) are inversely proportional:_______________________
_________________________________________________________________________
Wavelength and frequency can be inverconverted
λν = c
λ=
ν=
c=
𝑐
ν=λ
Photons:

____________ - tiny paricle of electromagnetic radiation – a bundle of light energy

____________ - electrons are at their lowest energy state in an atim

____________ - electrons have absorbed energy by “jumping” up to a higher energy state
in an atom
Light can travel as particles called photons
These particles absorb and emit light only in specific quanta ("packets" of energy)
Atomic Line Spectrum of Excited Hydrogen Atoms
__________________________
An object can gain or lose energy by absorbing or emitting radiant energy in_________

larger energy jumps produce shorter wavelegth (more energetic) light (see below)
The transfer of energy is quantized and can only occur in discrete units called quanta.
ΔE = hν =
ℎ𝑐
𝜆
ΔE =
Planck’s constant: h = 6.626 x 10-34 J · 𝑠
ν=
λ=
Say what?

Einstein’s experiment demonstrates the particle nature of light

Classical theory said that the E (energy) of ejected electrons should increase with an
increase in light intensity – this was not observed!
What happened:

No electrons were observed until light of a certain minimum E is used (threshold amount)

Number of e- ejected depends on light intensity
Line Spectra of Excited Atoms:

Excited Atoms emit light of only ____________ wavelengths

The wavelengths of light depend on the element
Example: Atomic Spectrum of Hydrogen:

_________________: Contains ____________ the wavelengths of light

_________________: (discrete) spectrum: contains only some of the
wavelengths of light
The diagram above present evidence for discrete energy levels about a nucleus. Electrons can only
be found in certain energy levels with certain energies.
Niels Bohr’s greatest contribution to science was
building a simple model of the atom. It was based on an understanding of the BRIGHT LINE
SPECTRA of excited atoms.
Bohr Model of the Atom:

_____________________: The lowest possible energy state for an atom (n = 1)

Higher energy electrons are in outer shells and easier to remove because they are more
shielded from the positive nucleus by the inner shell electrons.

Bohr’s model was incorrect - replaced by _______________________________
 e- cannot be exactly located – location based on ____________________
QUANTUM MECHANICS:
Major Players (including Bohr):

deBroglie (1924) – proposed that all moving objects have wave properties

Schrödinger applied the idea of e- behaving as a wave to the problem of electrons in atoms
Wave equation predicts:

Heisenberg solved problem of defining the nature of electrons in atoms

Cannot simultaneously define the position and momentum (m · v) of an electron

We define e- energy exactly but accept the limitation that we do not know exact
position
Failure of the Bohr Model:
The Bohr model of the atom paved the way for Quantum Mechanical Theory,
but current theory is in ______ way derived from the Bohr model of the atom.
Although is it a useful model to draw atoms, the Bohr model of the atom was
fundamentally incorrect – atoms do ______ move in circular orbits about the
nucleus.
Energy and Mass

Energy has Mass!
Equation:
E=
m=
c=
wave/particle duality of nature:
Ephoton
ℎ𝑐
=
mphoton =
𝜆
ℎ
𝜆𝑐
Energy changes in the H atom:
ΔE = Efinal state – Einital state
λ=
ℎ𝑐
𝛥𝐸