Download Chapter 7

Chapter 7
Quantum Theory of the Atom
Dr. S. M. Condren
Electromagnetic Radiation
Electromagnetic wave
• A wave of energy having a frequency within
the electromagnetic spectrum and
propagated as a periodic disturbance of the
electromagnetic field when an electric
charge oscillates or accelerates.
Dr. S. M. Condren
Electromagnetic Radiation
Electromagnetic wave
• wavelength
• frequency
• amplitude
Dr. S. M. Condren
Electromagnetic Radiation
nl= c
where
n => frequency
l => wavelength
c => speed of light
Dr. S. M. Condren
Wave Nature of the Electron
Dr. S. M. Condren
Electromagnetic Spectrum
Dr. S. M. Condren
Line Emission Spectrum
Dr. S. M. Condren
Line Spectrum
A spectrum produced by a luminous gas or
vapor and appearing as distinct lines
characteristic of the various elements
constituting the gas.
Dr. S. M. Condren
Emission Spectrum
The spectrum of bright lines, bands, or
continuous radiation characteristic of and
determined by a specific emitting substance
subjected to a specific kind of excitation.
Dr. S. M. Condren
Ground State
The state of least possible energy in a physical
system, as of elementary particles. Also
called ground level.
Dr. S. M. Condren
Excited State
Being at an energy level higher than the
ground state.
Dr. S. M. Condren
Photoelectric Effect
• the emission of electrons by substances,
especially metals, when light falls on their
surfaces.
Dr. S. M. Condren
Photoelectric Effect
Dr. S. M. Condren
Quantum Mechanics
Quantum theory
• the theory of the structure and behavior of
atoms and molecules.
Dr. S. M. Condren
Black Body Radiation
http://www.cbu.edu/~mcondren/C11599/BBvis.mov
Dr. S. M. Condren
Electromagnetic Radiation
Ehi - Elo = hc/l
where E => energy
h => Planck's constant
c => speed of light
l => wavelength
Dr. S. M. Condren
Photons
The quantum of electromagnetic energy,
generally regarded as a discrete particle
having zero mass, no electric charge, and an
indefinitely long lifetime.
Dr. S. M. Condren
Dispersion of White Light
Dr. S. M. Condren
The Atomic Spectrum of Hydrogen
and the Bohr Model
Bohr Model for the Hydrogen Atom
mnr = nh/2p
Dr. S. M. Condren
Bohr Atom
Dr. S. M. Condren
Bohr Model
E = -B/n2
where n => quantum number
1, 2, 3, 4, 5, 6, 7, etc
Dr. S. M. Condren
Bohr Model
for hydrogen
ground state: n = 1
excited state: n > 1
Dr. S. M. Condren
Bohr Model
E = (-2.179 X 10-18 J/part.)
(6.022 X 1023 part./mole)
(1 kJ/103 J)/n2
= (-1312 kJ/mol)(1/n2)
Dr. S. M. Condren
Electron Transition in a Hydrogen Atom
Lyman series => ultraviolet
n > 1 ==> n = 1
Balmer series => visible light
n > 2 ==> n = 2
Paschen series => infrared
n > 3 ==> n = 3
Dr. S. M. Condren
Line Spectra
See CHEMWORKS software
Dr. S. M. Condren
Absorption Spectrum
• Light shinning on a
sample causes
electrons to be excited
from the ground state
to an excited state
• wavelengths of that
energy are removed
from transmitted
spectra
Dr. S. M. Condren
Knowing diamond is transparent, which
curve best represents the absorption
spectrum of diamond (see below)?
A, B, C
Dr. S. M. Condren
According to the energy diagram below for
the Bohr model of the hydrogen atom, if an
electron jumps from E1 to E2, energy is
absorbed
emitted
not involved
Dr. S. M. Condren
Heisenberg, Werner
1901–76, German physicist
1932 Nobel Prize in physics
A founder of QUANTUM MECHANICS, he
is famous for his uncertainty principle,
which states that it is impossible to
determine both the position and momentum
of a subatomic particle (such as the
electron) with arbitrarily high accuracy.
Dr. S. M. Condren
Heissenberg Uncertainty Principle
“it is impossible to determine both the position
and momentum of a subatomic particle
(such as the electron) with arbitrarily high
accuracy”
The effect of this principle is to convert the
laws of physics into statements about
relative, instead of absolute, certainties.
Dr. S. M. Condren
Orbitals
• region of probability of finding an electron
around the nucleus
• 5 types => s p d f
• maximum of 2 electrons per orbital
Dr. S. M. Condren
Pure Atomic Orbitals
s
p
d
f
shape
# of orbitals / energy level
spherical
1
dumbbell
3
complex
5
very complex
7
Dr. S. M. Condren
Atomic Orbitals, s-type
Dr. S. M. Condren
Atomic Orbitals, p-type
Dr. S. M. Condren
Atomic Orbitals, d-type
Dr. S. M. Condren
Atomic Orbitals, f-type
Dr. S. M. Condren
Shapes of Orbitals
http://www.colby.edu/chemistry/OChem/DEMOS/Orbitals.html
Dr. S. M. Condren