Chapter 4 Section 2

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Transcript Chapter 4 Section 2

The Quantum
Model of the
Atom
Objectives
Discuss Louis de Broglie’s role in the development of
the quantum model of the atom
Compare & contrast the Bohr model and the quantum
model of the atom
Explain how the Heisenberg uncertainty principle and
the Schrödinger wave equation led to the idea of
atomic orbitals
List the four quantum numbers, and describe their
significance
Relate the number of sublevels corresponding to
each of an atoms main energy levels, the number of
orbitals per level, and the number of orbitals per main
energy level
To Summarize
Neils Bohr--Planetary model—electrons
arranged in circular paths (orbits) around the
nucleus
Answered Rutherford’s ?—electrons in a
particular path have a fixed energy, they do
NOT lose energy and fall into the nucleus
Energy level—region around nucleus where it
is likely to be moving, similar to rungs on a
ladder but not equally spaced
Quantum—amount of energy needed to
move an electron from its current energy level
to the next higher one
Electrons as Waves
Louis de Broglie—French scientist-1924
Electrons had a dual wave-particle
nature also
Waves can have only certain
frequencies
Electron waves have specific energies
(frequencies)—Bohr orbits
The Heisenberg
Uncertainty Principle
Werner Heisenberg—German physicist-1927
Where are the electrons?
Detecting electrons with light (photons)
interferes with its current path
Heisenberg uncertainty principle—it is
impossible to determine both the
position and velocity of an electron at
any one time
Difficult for scientists to accept at the time
Schrödinger Wave
Equation
Erwin Schrödinger—Austrian physicist—1926
Used math and quantum theory to
describe locations of electrons
Few if any analogies
States the probability of finding an
electron in a certain position—blurry cloud
Orbitals have quanta of energy but
electrons do not have specific locations
Atomic Orbitals &
Quantum Numbers
Orbital: 3-D region that indicates
probable location of an electron
Quantum numbers—specify the
properties of atomic orbitals and the
electrons they contain
Orbitals have different shapes and sizes
Principal quantum number, angular
momentum quantum number, magnetic
quantum number, spin quantum number
Principal Quantum
Number
Symbol: n
Indicates the main energy level of the
electron
Values are positive whole numbers only
1, 2, 3, etc.
Lower numbers mean lower energy
levels
Each main energy level has sublevels
Orbitals
Several electron cloud shapes are possible
because energy levels are divided into
energy sublevels
Each cloud shape is an atomic orbital—
region in space where there is a high
probability of finding an electron
s orbitals are spherical
p orbitals are dumbbell shaped
d and f orbitals are more complex
See p. 102-103
Orbitals
s sublevel has one orbital
p sublevel has three orbitals
d sublevel has five orbitals
f sublevel has seven orbitals
Each orbital can only have 2 electrons
Pictures of orbitals
http://home.montgomerybell.edu/%7Eneergaj/atomorbs.html
http://winter.group.shef.ac.uk/orbitron/
Animation of orbitals & electron emission spectra
http://www.glencoe.com/sites/common_assets/science/c
mc/cim/animations/ch5_2.rm