Chapter 7: Quantum Mechanical Model of Atom

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Chapter 7 Quantum Mechanical Model of Atom

• CHE 123 General Chemistry I
• Dr. Jerome Williams, Ph.D.
• Saint Leo University

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Overview

• Atomic Spectra
• Nature of Matter Energy

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Atomic Spectra

• Absorption vs. Emission Phenomenon
• Absorption energy is supplied to promote
  electrons from ground state (lowest energy level)
  into higher energy levels (excited states).
• Electrons prefer ground state (more stable).

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Atomic Spectra

• Absorption vs. Emission Phenomenon
• Emission excited electrons loses energy
  (usually by emitting light) and returns to a
  lower energy state or the ground state.
• Atoms give off light when heated or otherwise
  excited energetically thereby providing a clue
  as to their chemical makeup.

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Atomic Spectra

• Continuous Spectrum vs. Line Spectrum
• Continuous spectrum contains all wavelengths of
  visible light. Observed as white light.
• Line spectrum contains specific wavelengths that
  result in a unique fingerprint that is used to
  identify elements. No two elements have the exact
  same line spectrum.

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Atomic Spectra
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Atomic Spectra
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Atomic Spectra

• Wavelength values found using Balmer-Rydberg
  Equation
• 1/? R 1 / m2 1 / n2
• R Rydberg Constant
• (R 1.097 x 10-2 nm-1)
• The values (m n) are integers such that ngtm

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Nature of Matter Energy

• Relationship between energy, frequency, and
  wavelength.
• Developed by two physicists (Max Planck Albert
  Einstein)

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Nature of Matter Energy

• Max Planck proposed that matter energy are not
  distinct in nature they can be looked upon as
  one in the same.
• Energy is only emitted in discrete packets called
  quanta.
• E n h ? n h c / ? h 6.626 x 10-34 J sec

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Nature of Matter Energy

• Albert Einstein used the idea of quanta to
  explain the photoelectric effect.
• He proposed that light behaves as a stream of
  particles called photons.
• Also known for famous E mc2

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Nature of Matter Energy

• Louis deBroglie used work of Planck Einstein
  to propose the wave-particle duality concept.
• He suggested waves can behave as particles and
  particles can behave as waves.
• For a particle ? h / m v
• For light ? h / m c