1. Section 2: Quantum Theory and the Atom
Wavelike properties of electrons help relate atomic emission spectra, energy states of atoms, and atomic orbitals. K
What I Know W
What I Want to Find Out L
What I Learned

2. Essential Questions
How do the Bohr and quantum mechanical models of the atom compare?
What is the impact of de Broglie’s wave-particle duality and the Heisenberg uncertainty principle on the current view of electrons in atoms?
What are the relationships among a hydrogen atom’s energy levels, sublevels, and atomic orbitals?
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Quantum Theory and the Atom

3. Vocabulary Review New atom ground state quantum number
de Broglie equation
Heisenberg uncertainty principle
quantum mechanical model of the atom
atomic orbital
principal quantum number
principal energy level
energy sublevel
Quantum Theory and the Atom
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4. Bohr’s Model of the Atom
Einstein’s theory of light’s dual nature accounted for several unexplainable phenomena but not why atomic emission spectra of elements were discontinuous rather continuous.
In 1913, Niels Bohr, a Danish physicist working in Rutherford’s laboratory, proposed a quantum model for the hydrogen atom that seemed to answer this question.
Bohr correctly predicted the frequency lines in hydrogen’s atomic emission spectrum.
The lowest allowable energy state of an atom is called its ground state.
When an atom gains energy, it is in an excited state.
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Quantum Theory and the Atom

5. Bohr’s Model of the Atom
Bohr suggested that an electron moves around the nucleus only in certain allowed circular orbits.
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Quantum Theory and the Atom

6. Bohr’s Model of the Atom
Each orbit was given a number, called the quantum number.
Hydrogen’s single electron is in the n = 1 orbit in the ground state.
When energy is added, the electron moves to the n = 2 orbit.
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Quantum Theory and the Atom

7. Bohr’s Model of the Atom
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Quantum Theory and the Atom

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The Balmer Series
Concepts in Motion
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Quantum Theory and the Atom

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Electron Transitions
Concepts in Motion
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Quantum Theory and the Atom

10. Bohr’s Model of the Atom
The limits of Bohr’s model
Bohr’s model explained the hydrogen’s spectral lines, but failed to explain any other element’s lines.
The behavior of electrons is still not fully understood, but substantial evidence indicates they do not move around the nucleus in circular orbits.
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Quantum Theory and the Atom

11. The Quantum Mechanical Model of the Atom
Louis de Broglie (1892–1987) hypothesized that particles, including electrons, could also have wavelike behaviors.
The figure illustrates that electrons orbit the nucleus only in whole- number wavelengths.
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Quantum Theory and the Atom

12. The Quantum Mechanical Model of the Atom
The de Broglie equation predicts that all moving particles have wave characteristics.
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Quantum Theory and the Atom

13. The Quantum Mechanical Model of the Atom
Heisenberg showed it is impossible to take any measurement of an object without disturbing it.
The Heisenberg uncertainty principle states that it is fundamentally impossible to know precisely both the velocity and position of a particle at the same time.
The only quantity that can be known is the probability for an electron to occupy a certain region around the nucleus.
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Quantum Theory and the Atom

14. The Quantum Mechanical Model of the Atom
Schrödinger treated electrons as waves in a model called the quantum mechanical model of the atom.
Schrödinger’s equation applied equally well to elements other than hydrogen.
The wave function predicts a three-dimensional region around the nucleus called the atomic orbital.
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Quantum Theory and the Atom

15. Hydrogen Atomic Orbitals
Principal quantum number (n) indicates the relative size and energy of atomic orbitals.
n specifies the atom’s major energy levels, called the principal energy levels.
Energy sublevels are contained within the principal energy levels.
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Quantum Theory and the Atom

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Fireworks
Concepts in Motion
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Quantum Theory and the Atom

17. Hydrogen Atomic Orbitals
Each energy sublevel relates to orbitals of different shape.
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Quantum Theory and the Atom

18. Hydrogen Atomic Orbitals
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Quantum Theory and the Atom

19. Review Essential Questions Vocabulary
How do the Bohr and quantum mechanical models of the atom compare?
What is the impact of de Broglie’s wave-particle duality and the Heisenberg uncertainty principle on the current view of electrons in atoms?
What are the relationships among a hydrogen atom’s energy levels, sublevels, and atomic orbitals?
Vocabulary
ground state
quantum number
de Broglie equation
Heisenberg uncertainty principle
quantum mechanical model of the atom
atomic orbital
principal quantum number
principal energy level
energy sublevel
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Quantum Theory and the Atom