Unit 3 – Electron Configurations
Part C: Quantum Mechanical Model
River Dell Regional High School
Background
Problem With the Bohr Model –Why and
how could the electron in hydrogen orbit in
only a small number of allowed paths?
Solving the Problem
1. Louis de Broglie – electrons have a
dual nature - they can act like
particles or waves !!!
Duality of Electrons
Cathode Ray Tube Experiment
(by JJ Thomson):
• Electrons travel at high
speed.
• Electrons have fixed mass.
All important attributes for particles.
Duality of Electrons
Electron beam behaves like waves.
Heisenberg Uncertainty Principle
How can police tell the speed of a moving vehicle?
Heisenberg Uncertainty Principle
How can we tell the speed of a moving electron?
Before
Photon
Moving
Electron
After
Photon
changes
wavelength
Electron Changes
Velocity
Heisenberg Uncertainty Principle
Both the velocity and
position of a particle
(electron) can not be
measured at the same time.
Werner Heisenberg
1901-1976
Quantum Mechanical Model
Schrodinger – developed
equations that treat electrons in
atoms like waves.
• describe the shapes of the
orbitals in which electrons
have a high probability of
being found.
• quantum theory –
mathematical explanation for
the wave properties of
electrons that apply to all
atoms.
Erwin Schrodinger
1887-1961
Quantum Mechanical Model
 The nucleus is found inside
a blurry “electron cloud”
 A area where there is a
chance of finding an
electron
Principles of the Quantum Model
1. Electrons act like waves and particles.
2. Probability of an electron being found
at various distances from the nucleus.
3. orbitals – a 3-D region about the
nucleus where a specific electron may
be found.
Principles of the Quantum Model
4.Electrons have greater energy as their distance
from the nucleus increases.
5.Energies of orbitals are quantized within main
energy levels.
6.The exact location of electrons can not be
pinpointed – they are found in regions of high
probability called orbitals or electron clouds.
Similarities -Bohr and Quantum Model
1.The closer the orbital to the nucleus the lower the
energy.
2.To move from a lower to a higher level the energy
absorbed must be equal to the difference between
the levels.
3.When e- drops from a higher to lower level
electromagnetic radiation is emitted equal to the
difference in energy levels.
4.The most probable location of the e- is a distance
equal to the lowest energy level.
Quantum Mechanical Model
• According to Schrödinger’s calculations, four
quantum numbers are needed to fully resolve the
wave function mathematically for each electron in
any given atom.
• Meaning – there is a unique set of four quantum
numbers to fully describe the behavior of an
electron.
Four Quantum Numbers
A. Principal Quantum Number (n)
main energy level
B. Orbital Quantum Number (l)
shape of orbital (s, p, d, f)
C. Magnetic Quantum Number (m)
orientation of orbital about the nucleus
D. Spin Quantum Number (s)
indicates clockwise or counter-clockwise spin of the electron
(+½ or –½)
Summary
• Wave and particle duality of electrons.
• Heisenberg Uncertainty Principle.
• Schrodinger’s Quantum Mechanical Model of Atoms.