1. The Quantum Model of the Atom

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. Pictures of orbitals
Animation of orbitals & electron emission spectra