1. Chemistry Notes
The Quantum Theory

2. The Bohr Model
Recall: Bohr’s model describes the atom as having definite energy levels
e- will absorb a “quantized” amount of energy, which excites the e-,when e- returns to its ground state it always emits light at specific wavelengths
These wavelengths correspond to definite changes in the electrons energy
Bohr used Max Plank’s idea: E = hc/λ
Bohr’s model refers to quanta as packets of energy (or particles)

3. From Bohr to the Quantum Model
Bohr’s model had issues
considers electrons to have both a known radius and orbit
It makes poor predictions regarding the spectra of larger atoms.
It does not predict the relative intensities of spectral lines.
The Bohr Model does not explain fine structure in spectral lines.

4. From Bohr to the Quantum Model
Heisenberg Uncertainty Principle: it is impossible to know the exact position and the exact momentum of an electron at the same time. (This challenged Bohr’s Model)
In order to know where an electron is we have to “see” it. To see something it must be hit by a photon. Photons and electrons are roughly the same size, when they collide the electron will no longer be in the same position.

5. From Bohr to the Quantum Model
Photoelectric Effect showed that r frequency high light can eject electrons.
i.e. – Light can act as a particle  See Physics notes
De Broglie – can quanta (particles) have wave properties? Can particles act like waves?
Wave-particle duality

6. From Bohr to the Quantum Model
Erwin Schrodinger investigated the wave nature of the electron
Developed a mathematical equation that related the electron's amplitude to any point in space around the nucleus

7. Schrodinger's Equation
Ψ is the wave function or probable position of the electron.
m is the mass of the electron.
E is the total energy of the system.
V is the potential energy and is a function of x, y and z.
The probability of finding the electron decreases as you move away from the center of the nucleus.

8. Schrodinger's Equation
The solutions of the Schrodinger equation can tell us things about the electron.
The size of electron cloud
The energy of the electron cloud
The shape of the cloud

9. The Quantum Model
Summary: Quantum model seeks to describe the behavior of subatomic particles in terms of waves
Electrons have properties of both waves and particles

10. The Quantum Model
Bohr’s model showed definite positioning of electrons (they were in orbits).
The Quantum model is primarily a mathematical one that shows the probable location of an electron
Notice: the circles denote the probability of finding an electron in that region of space.

11. The Quantum Model
A fuzzy cloud represents the probability of finding an electron within a certain volume of space.
This Fuzzy Cloud is called an orbital
Denser cloud = higher probability of finding an electron
Less dense cloud = lower probability of finding an electron

12. The Quantum Model Orbits (Bohr’s Model) vs. Orbitals (Quantum Model)
(PATHS e- travel in (Regions of space where e- may be)

13. The Quantum Model Letters that denote atomic orbitals in sublevels:
s – spherical shaped
p – dumbbell shaped (3 orbitals)
d – four of the five kinds of d orbitals are clover shaped. (5 orbitals)
f – very oddly shaped (7 orbitals)
The maximum number of electrons in each orbital is 2.

17. AGAIN!!!
The Quantum Theory is not trying to show what the atom looks like.
The QT is a mathematical model
The QT is trying to show us the probable location of electrons in an atom
The orbitals represent the probability of finding an electron

19. Describing the Distribution of Electrons
Quantum Numbers: like a zip code for electrons
n (principle quantum number)– Indicates principle energy level
Describes relative size of the electron cloud
Corresponds to the energy level 1,2,3,…n

20. Describing the Distribution of Electrons
l (second quantum number) – Indicates sublevel
Describes shape of cloud
s: l = 0; p: l = 1; d: l = 2; f: l = 3

21. Describing the Distribution of Electrons
m (third quantum number) – Indicates orientation in space of the cloud
For the p orbitals the values range from –1 to 1
px (-1) / py (O) / pz (+1)
For the d orbitals the values range from –2 to 2
dx2y2 (+2) / dz2 (+1) / dxy (O) / dxz (-1) / dyz (-2)
For the f orbitals the values range from –3 to 3
Don’t worry about it.

22. Describing the Distribution of Electrons
s (fourth quantum number) - distinguish between electrons in same orbital.
+1/2 denotes a clockwise spin
-1/2 denotes a counter clockwise spin.
The Pauli exclusion principal says: electrons in the same orbital have opposite spins. (See Fig on p. 123 in book)

23. Describing the Distribution of Electrons
What do the following numbers tell us: 4, 1, -1, +1/2
Electron is in the 4th PEL
Electron is in the p sublevel
Electron is oriented in the orbital along x-axis
Electron has a clockwise spin

24. Describing the Distribution of Electrons
Quantum numbers are like zip codes
N  United States / PEL
L  Michigan / sublevel
M  Bridgman / orbital
S  facing north / spin
See table 5.1 in book
Please read pages

26. The Quantum Theory Summary
Explain how the quantum model is part of the on going development of the atomic model.
State the Heisenburg Uncertainty Principle and explain how it influenced the modern view of the atom.
Explain how the Quantum Model is different than other views of the atom.
Use quantum numbers to locate the approximate location of electrons.