Transcript Section 5.2
Section 5-2 Quantum Theory and the Atom Objectives • Compare the Bohr and quantum mechanical models of the atom • Explain the impact of de Broglie’s waveparticle 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 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 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 Bohr Model of the Atom • Energy is added to an atomelectron 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 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 Quantum Mechanical Model of the Atom • In 1924 Louis de Broglie proposed that electrons, like light also had a particlewave dual nature. • de Broglie noticed only multiples of half wavelengths are allowed in circular orbits 1 half-wavelength 2 half-wavelengths 3 half-wavelengths 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. h mv Quantum Mechanical Model of the Atom • Broglie’s revelation still could not accurately model electron behavior of elements more complex than Hydrogen. 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 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 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 Look at Figure 5-14 (p. 132) 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 Look at Table 5-2 (p. 134) Assignment • P.134 #13-17 – Make sure to answer ALL parts of the question and use complete sentences!!