The Bohr Model, Wave Model, and Quantum Model Sections 6.3-6.5 The Bohr Model, Wave Model, and Quantum Model

Objectives Draw Bohr Models Describe the wave behavior of matter Arrange electrons in an atom Identify energy levels Apply Heisenberg’s Uncertainty Principle Describe the quantum mechanical model

Key Terms Ground state Excited states Matter waves momentum Uncertainty principle Wave functions Probability density Electron density Orbitals Electron shell subshell

Bohr Model of the Atom In 1913 Niels Bohr proposed quantum model for the H atom Bohr proposed H atom has only certain allowable energy states Lowest state= ground state Gaining energy = excited state

Bohr Model of the Atom Electrons move in certain, specific, circular orbitals Smaller orbit = lower 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

Bohr Model of the Atom Energy is added to an atomelectron moves to higher energy level 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

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

De Broglie 1924 Electrons, like light also had a particle-wave dual nature Only multiples of half wavelengths are allowed in circular orbits

1 half-wavelength 2 half-wavelengths 3 half-wavelengths

De Broglie Formulated an equation for the wavelength, mass, and velocity of a particle

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

Quantum Mechanical Model 1926 Schrödinger Limited electrons to only certain energy levels Atomic orbital: 3 dimensional area around the nucleus that predicts the 90 % PROBABLE location of an electron

Electron Density Diagram

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

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

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

s and p orbitals

Three p orbitals

d orbitals

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