Section 5-2 Quantum Theory and the Atom. Objectives Compare the Bohr and quantum mechanical models...
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Transcript of Section 5-2 Quantum Theory and the Atom. Objectives Compare the Bohr and quantum mechanical models...
![Page 1: 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 wave-](https://reader036.fdocuments.in/reader036/viewer/2022081513/56649f465503460f94c680a3/html5/thumbnails/1.jpg)
Section 5-2
Quantum Theory and the Atom
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Objectives• Compare the Bohr and quantum
mechanical models of the atom• Explain the impact of de Broglie’s
wave-particle 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
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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
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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
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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
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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
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Quantum Mechanical Model of the Atom
• In 1924 Louis de Broglie proposed that electrons, like light also had a particle-wave dual nature.
• de Broglie noticed only multiples of half wavelengths are allowed in circular orbits
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1 half-wavelength
2 half-wavelengths
3 half-wavelengths
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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.
mv
h
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Quantum Mechanical Model of the Atom
• Broglie’s revelation still could not accurately model electron behavior of elements more complex than Hydrogen.
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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
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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
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Electron Density Diagram
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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
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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
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Look at Figure 5-14 (p. 132)
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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
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s and p orbitals
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Three p orbitals
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d orbitals
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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
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Look at Table 5-2 (p. 134)
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Assignment• P.134 #13-17
– Make sure to answer ALL parts of the question and use complete sentences!!