Download Chapter 7 - Colby College Wiki

Chapter 7:
Atoms and Light
Electromagnetic Radiation
Low ν
High ν
WMHB broadcasts at 89.7 on the FM
dial (89.7 MHz). What is the
wavelength of the emitted radio waves?
The AM dial ranges from 500-1800 kHz.
What wavelengths does this represent?
A microwave oven (2.4 GHz)?
Electromagnetic Spectrum
Constructive and Destructive Interference
Atomic Spectra
Hydrogen
Helium
Lithium
Sodium
Potassium
Atomic Spectra
The Hydrogen Atomic Spectrum
Quantum Theory (Blackbody Radiation)
Max Planck: E = hν
The energy required to break a carboncarbon bond is approximately 360
KJ/mol. What wavelength of electromagnetic radiation can supply this amount
of energy?
The Photoelectric Effect
• Heinrich Hertz (1888) discovered that light striking the surface of
certain metals causes ejection of electrons - the photoelectric effect.
• Electrons were only ejected if the frequency of the light (v) was above
a certain threshold frequency (vo)
• The number of electrons ejected were proportional to the intensity of
the light
• The velocity (kinetic energy) of the electrons ejected was proportional
to the frequency of the light
• Einstein used Planck’s ideas to explain the photoelectric effect:
ΔE = hν-hνo
Emission and Absorption Spectroscopy
The Bohr Atom
Hydrogen Energy Levels
E = (-2.18 X 10-18 J)
1
l
= (RH)
1
ni2
–
1
n2
1
nf2
A New Quantum Mechanics
The Heisenberg Uncertainty Principle
h
Δx Δp ≥
4π
Standing Waves
In a standing wave, the nodes remain at a constant
position.
2L
l=
n
n = 1, 2, 3…
Standing Waves
Shrodinger suggested that electrons can be described
as standing waves orbiting the nucleus, and used a
mathematical equation to represent these waves.
The Schrodinger Equation:
Wave Functions
 (psi), the wave function.
Corresponds to a standing wave within
the boundary of the system being
described.
The energy of the standing wave
increases as we add more nodes.
Probability of Finding an Electron
Quantum Numbers
By using three different quantum numbers, we can describe the
wavefunction of any electron in an atom.
n : the principle quantum number
Designates electronic shell (distance from nucleus), n = 1, 2, 3…
[It also corresponds to the number of radial nodes]
l : The angular momentum quantum number
Designates the shape of the orbital, l = 0, 1, 2…(n-1)
ml : The magnetic quantum number
Describes the orientation of the orbital; ml = - l …-2, -1, 0, 1, 2…+l
l
= 0, the “s” orbitals
l
= 1, the “p” orbitals
m for the “p” orbitals
l
l
= 2, the “d” orbitals
Orbital Occupancy
Each orbital (described by 3 quantum numbers) can contain
two electrons.
No two electrons can have the same set of quantum numbers.
Therefore…
The Fourth Quantum Number, s
Electrons have a spin of either +1/2 or –1/2. Electrons that
occupy the same orbital must have opposite spins.