Download 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 (1913)
• Proposed the quantum model for H
• Based on Planck/ Einstein’s quanta energy
• H atom has only certain allowable energy states
• Lowest = ground state
• Gaining energy = excited state
Continued
• 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
De Broglie (1924)
• Electrons, like light, have particle-wave dual
nature
• Only multiples of 1/2 wavelengths allowed in
circular orbits
1 half-wavelength
2 half-wavelengths
3 half-wavelengths
Continued
• All moving particles behave like waves
• Wave characteristics decrease as mass increases
h

mv
Heisenberg Uncertainty
Principle
–Fundamentally impossible to know
precisely both velocity AND position of a
particle at the same time
–Cannot measure an object without
disturbing it
Schrödinger (1926)
• Quantum mechanical model
–Limited electrons to only certain
energy levels
Quantum Mechanical Model
• Principal quantum numbers (n)
– n = number of principle energy levels
– Lowest level= ground state= n= 1
• Inside of principle energy levels are sublevels
– s, p, d, f
• Inside sublevels are orbitals
– s has 1, p has 3, d has 5, f has 7
• Inside each orbital are 2 electrons
s orbital
Three p orbitals
Five d orbitals
Seven f orbitals
Look at Table 5-2 (p. 134)