Transcript III. Quantum Model of the Atom

Ch. 4 - Electrons in Atoms
III. Quantum
Model
of the Atom
Chpt. 5
A. Electrons as Waves
Louis de Broglie (1924)
 Applied wave-particle theory to e e- exhibit wave properties
QUANTIZED WAVELENGTHS
A. Electrons as Waves
QUANTIZED WAVELENGTHS
A. Electrons as Waves
EVIDENCE: DIFFRACTION PATTERNS
Whoa! They produce
they SAME pattern!
VISIBLE LIGHT
ELECTRONS
B. Quantum Mechanics
Heisenberg Uncertainty Principle
 Impossible to know both the velocity and
position of an electron at the same time
B. Quantum Mechanics
Schrödinger Wave Equation (1926)
 finite # of solutions  quantized energy
levels
 defines probability of finding an e-
Ψ 1s 

1 Z 3/2 σ
π a0
e
B. Quantum Mechanics
Orbital (“electron cloud”)
 Region in space where there is 90%
probability of finding an e-
Orbital
Radial Distribution Curve
C. Quantum Numbers
Four Quantum Numbers:
 Specify the “address” of each electron in
an atom
C. Quantum Numbers
1. Principal Quantum Number ( n )
 Energy level
 Size of the orbital
 n2 = # of orbitals in
the energy level
C. Quantum Numbers
2. Angular Momentum Quantum # ( l )
 Energy sublevel
 Shape of the orbital
s
p
f orbital can really can only be
represented as a 3-d model!
d
f
C. Quantum Numbers
3. Magnetic Quantum Number ( ml )
 Orientation in x, y, z planes
 Specifies the exact orbital within each
sublevel
X orientation
Y orientation
Z orientation
C. Quantum Numbers
 d-sublevels have multiple orientations
due to the different combinations of
x,y,z planes---all reduce to 5 different
shapes.
C. Quantum Numbers
 As you might suspect, the number of
orientations & their complexity increases
as orbitals increase in energy.
 This means that f orbitals have 7 different
orientations.
 They are so complex that they cannot be
accurately illustrated on paper using only
2 dimensions----they are weird looking.
C. Quantum Numbers
Orbitals combine to form a spherical
shape.
2px
2py
2s
2pz
C. Quantum Numbers
4. Spin Quantum Number ( ms )
 Electron spin  +½ or -½
 An orbital can hold 2 electrons that spin
in opposite directions.
C. Quantum Numbers
Pauli Exclusion Principle
 No two electrons in an atom can have
the same 4 quantum numbers.
 Each e- has a unique “address”:
1. Principal #
2. Ang. Mom. #
3. Magnetic #
4. Spin #




energy level
sublevel (s,p,d,f)
orbital
electron
Electron Configurations
Systematic way of putting an “address” on each e-.
The aufbau principle states that each electron occupies
the lowest energy orbital available.
When all the orbitals
combine they overlap
& look like …….
Feeling overwhelmed?
Read pp.
149-155!
“Teacher, may I be excused? My brain is full.”