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**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

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6(A) Understand the experimental design and conclusions used in the development of modern atomic theory, including Dalton’s Postulates, Thomson’s discovery of electron properties, Rutherford’s nuclear atom, and Bohr’s nuclear atom. 6(C) Calculate the wavelength, frequency, and energy of light using Planck's constant and the speed of light. 3(F) Research and describe the history of chemistry and contributions of scientists. Copyright © McGraw-Hill Education Quantum Theory and the Atom

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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? Copyright © McGraw-Hill Education Quantum Theory and the Atom

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**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 Copyright © McGraw-Hill Education

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**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. Copyright © McGraw-Hill Education Quantum Theory and the Atom

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**Bohr’s Model of the Atom**

Bohr suggested that an electron moves around the nucleus only in certain allowed circular orbits. Copyright © McGraw-Hill Education Quantum Theory and the Atom

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**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. Copyright © McGraw-Hill Education Quantum Theory and the Atom

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**Bohr’s Model of the Atom**

Copyright © McGraw-Hill Education Quantum Theory and the Atom

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**Add link to concepts in motion animation from page 147 here.**

The Balmer Series Concepts in Motion FPO Add link to concepts in motion animation from page 147 here. Copyright © McGraw-Hill Education Quantum Theory and the Atom

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Electron Transitions Energy levels are similar to the rungs of a ladder. The four visible lines correspond to electrons dropping from a higher n to the orbit n = 2. As n increases, the hydrogen atom’s energy levels are closer to each other. Copyright © McGraw-Hill Education Quantum Theory and the Atom

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**Add link to concepts in motion animation from page 148 here.**

Electron Transitions Concepts in Motion FPO Add link to concepts in motion animation from page 148 here. Copyright © McGraw-Hill Education Quantum Theory and the Atom

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**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. Copyright © McGraw-Hill Education Quantum Theory and the Atom

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**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. Copyright © McGraw-Hill Education Quantum Theory and the Atom

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**The Quantum Mechanical Model of the Atom**

The de Broglie equation predicts that all moving particles have wave characteristics. Copyright © McGraw-Hill Education Quantum Theory and the Atom

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**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. Copyright © McGraw-Hill Education Quantum Theory and the Atom

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**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. Copyright © McGraw-Hill Education Quantum Theory and the Atom

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**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. Copyright © McGraw-Hill Education Quantum Theory and the Atom

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**Add link to video from page 153 here.**

Fireworks Concepts in Motion FPO Add link to video from page 153 here. Copyright © McGraw-Hill Education Quantum Theory and the Atom

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**Hydrogen Atomic Orbitals**

Each energy sublevel relates to orbitals of different shape. Copyright © McGraw-Hill Education Quantum Theory and the Atom

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**Hydrogen Atomic Orbitals**

Copyright © McGraw-Hill Education Quantum Theory and the Atom

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**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? 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 Copyright © McGraw-Hill Education Quantum Theory and the Atom

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