1. Quantum Theory and the Atom
Section 5-2
Quantum Theory and the Atom

2. Objectives Compare the Bohr and quantum mechanical models of the atom
Explain the impact of de Broglie’s wave-particle duality and the Heisenberg uncertainty principle on the modern view of electrons in atoms
Identify the relationships among a hydrogen atom’s energy levels, sublevels, and atomic orbitals

3. Bohr Model of the Atom
In 1913 Niels Bohr proposed quantum model for the H atom
Based on Planck and Einstein’s ideas of quantitized energy
Bohr proposed H atom has only certain allowable energy states
Lowest state= ground state
Gaining energy = excited state

4. Bohr Model of the Atom
Electrons move in certain, specific, circular orbitals
Smaller the orbit = lower the energy level
Assigned the allowable electron orbitals the principle quantum number, n.
1st orbit= lowest energy: n=1
2nd orbit= 2nd lowest energy: n=2

5. Bohr Model of the Atom
Energy is added to an atomelectron moves to higher energy level in an “excited state”
Electron in “excited state” drops to a lower energy orbit emits a photon
E = E higher-energy orbit – E lower-energy orbit= E photon= h

7. Bohr Model of the Atom Problems with Bohr’s model
Only explained the atomic emission spectra of H
Did not explain why electrons should only be allowed certain, specific energy levels

8. Quantum Mechanical Model of the Atom
In 1924 Louis de Broglie proposed that electrons, like light also had a particle-wave dual nature.
de Broglie noticed only multiples of half wavelengths are allowed in circular orbits

10. 1 half-wavelength
2 half-wavelengths
3 half-wavelengths

11. Quantum Mechanical Model of the Atom
de Broglie formulated an equation for the wavelength, mass, and velocity of a particle
Moving particles’ wave characteristics decrease as mass increases.

12. Quantum Mechanical Model of the Atom
Broglie’s revelation still could not accurately model electron behavior of elements more complex than Hydrogen.

13. Heisenberg Principle Uncertainty
Fundamentally impossible to know precisely both the velocity AND position of a particle at the same time.
Cannot measure an object without disturbing it

14. Schrödinger Wave Equation
In 1926 Erwin Schrödinger created the quantum mechanical model.
Limited electrons to only certain energy levels
Atomic orbital: 3 dimensional area around the nucleus that predicts the 90 % PROBABLE location of an electron

15. Electron Density Diagram

16. Quantum Mechanical Model
Assigns principal quantum numbers (n) relative to sizes and energies of orbitals
(n) specifies atom’s major energy levels= principle energy levels
Lowest level= ground state= n= 1
H has 7 energy levels, n= 1 to 7

17. Quantum Mechanical Model
Principal energy levels contain energy sublevels
Principal energy level 1 has 1 sublevel
Principal energy level 2 has 2 sublevels
Principal energy level 3 has 3 sublevels

18. Look at Figure 5-14 (p. 132)

19. Energy Sublevels s, p, d, and f
Labeled according to shapes of orbitals
s = spherical
p = dumbbell
d and f = not all have same shape

20. s and p orbitals

21. Three p orbitals

22. d orbitals

23. Energy Sublevels Each orbital contains 2 electron at most
Principal energy level 1 has 1 sublevel: 1s orbital
Principal energy level 2 has 2 sublevels: 2s and 2p
2p sublevel has 3 dumbbell-shaped p orbitals (2px, 2py, and 2pz)
Principal energy level 3 has 3 sublevels: 3s, 3p, and 3d
d sublevels have 5 orbitals
Principal energy level 4 has 4 sublevels: 4s, 4p, 4d, and 4f
f sublevels have 7 orbitals

24. Look at Table 5-2 (p. 134)

25. Assignment
P.134 #13-17
Make sure to answer ALL parts of the question and use complete sentences!!