The Quantum Model of the Atom

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. 102-103

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 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/cmc/cim/animations/ch5_2.rm