The Quantum Model of the

Atom

Objectives

Discuss Louis de Broglie’s role in the development of the quantum model of the atomCompare & contrast the Bohr model and the quantum model of the atomExplain how the Heisenberg uncertainty principle and the Schrödinger wave equation led to the idea of atomic orbitalsList the four quantum numbers, and describe their significanceRelate 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

To SummarizeNeils 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

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

The Heisenberg Uncertainty Principle

Werner Heisenberg—German physicist-1927

Where are the electrons?Detecting electrons with light (photons) interferes with its current pathHeisenberg uncertainty principle—it is Heisenberg uncertainty principle—it is impossible to determine both the impossible to determine both the position and velocity of an electron at position and velocity of an electron at any one timeany one timeDifficult for scientists to accept at the time

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

OrbitalsOrbitals have quanta of energy but electrons do not have specific locations

Atomic Orbitals & Quantum Numbers

OrbitalOrbital: 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 sizesPrincipal quantum numberPrincipal quantum number, angular momentum quantum number, magnetic quantum number, spin quantum number

Principal Quantum Number

Symbol: nIndicates the main energy level of the electronValues are positive whole numbers only1, 2, 3, etc.Lower numbers mean lower energy levelsEach main energy level has sublevels

OrbitalsSeveral 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

ss orbitals are spherical

pp orbitals are dumbbell shaped

dd and ff orbitals are more complex

See p. 102-103

Orbitals

ss sublevel has one orbital

pp sublevel has three orbitals

dd sublevel has five orbitals

ff sublevel has seven orbitals

Each orbital can only have 2 electrons

http://home.montgomerybell.edu/%7Eneergaj/atomorbs.html

Pictures of orbitals

http://winter.group.shef.ac.uk/orbitron/

http://www.glencoe.com/sites/common_assets/science/cmc/cim/animations/ch5_2.rm

Animation of orbitals & electron emission spectra