Transcript Quantum Mechanical Model of the Atom

QUANTUM MECHANICS
MAX PLANCK and the
QUANTUM
• electromagnetic
energy could be
emitted only in
quantized form
• E = hf, where E is
energy, h is Planck's
constant and f is the
frequency of the
radiation.
Definition
• Quantum: an indivisible entity.
The magnitude can only take on certain
discrete numerical values
•The term “photon” was
coined in 1926 by Gilbert
Lewis
•The QUANTUM of the
electromagnetic field.
Photons have zero mass and zero electric
charge
Photons do carry energy, momentum and
angular momentum
Photons are produced when one electron
moves to an orbital of less energy
And when an unstable nucleus undergoes
nuclear decay
And wherever charged particles are
accelerated
And atoms continuously emit photons due
to their collisions with each other
HYDROGEN
LINE SPECTRUM
Hydrogen
Neon
Nitrogen
Argon
Electromagnetic Spectrum
THE WAVE-LIKE
ELECTRON
•Louis Victor de BroglieFrench Theoretical Physicist
•1924 doctoral thesis,
Recherches sur la théorie des
quanta (Research on Quantum
Theory), introduced his theory
of electron waves.
•Included the Wave-Particle
Duality Theory of matter
WAVE-PARTICLE DUALITY
All objects exhibit, at times, a
wave-like nature, and at other
times a particle-like nature.
•Photon acts like a PARTICLE
•Photon acts like a WAVE
•de Broglie suggested that
there is a wave associated
with the moving electron.
The de Broglie Hypothesis
Any moving particle or
object has an associated
wavelength
•Not long after de Broglie showed that
the electron could be connected with the
wave, Heisenberg and Schrodinger
described the waves mathematically.
•Their formulas very closely match the
experimental observations.
Heisenberg Uncertainty Principle
One cannot assign, with full
precision, values for certain pairs
of observable variables, including
momentum and position, of a
single particle at the same time.
Schrödinger Wave Equation
Schrödinger Wave Equation
Leads to a series of mathematical
functions called “wave functions”,
Ψ.
Ψ2 provides information about an
electron’s location in an allowable
energy state.
Ψ2 = probability density
THE
QUANTUM
MECHANICAL
MODEL OF
THE ATOM
QUANTUM NUMBERS
• Principal Quantum Number (n)
refers to size and energy of orbital
• Angular Quantum Number (l)
Distinguishes the shape of the orbitals
• Magnetic Quantum Number (ml)
distinguishes orientation in space
• Spin Quantum Number (ms)
gives the 2 possible locations of the spin
axis
The s Orbital
The p Orbital
The d Orbitals
The f Orbitals
• much more complicated in their shape.
• so much so that we are not going to
worry about them in this course!!!!!
•The maximum number of electrons that
can occupy a certain energy level can be
calculated from the equation 2n2
•Pauli Exclusion Principal: an
atomic orbital may be described
at most by two electrons
•Aufbau Principal: electrons must enter
orbitals of lowest energy first
•Hund’s rule: when electrons occupy
orbitals of equal energy, one electron enters
each orbital until all the orbitals contain
one electron with spins parallel. Then other
electrons enter the orbitals with opposite
spins.
Arthur Compton
The Compton Effect:
When a high energy xray photon collides
with a “free electron”,
it gives some of its
energy to the electron
and a lower energy
photon scatters off the
electron.
Momentum of a Photon
the momentum of a photon is the quotient
of Plank’s constant and the wavelength of
the photon
P = h/λ
Page 857
References
• http://hyperphysics.phyastr.gsu.edu/hbase/ems1.html
• www.wikipedia.org
• http://theory.uwinnipeg.ca/mod_tech/node154.html
• http://library.thinkquest.org/19662/high/eng/electro
n-wave.html
• http://www.chemguide.co.uk/atoms/properties/atom
orbs.html