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happyphysics.com Physics Lecture Resources Prof. Mineesh Gulati Head-Physics Wing Happy Model Hr. Sec. School, Udhampur, J&K Website: happyphysics.com

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Ch 42 Molecules and Condensed Matter © 2005 Pearson Education

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42.1 Types of Molecular Bonds Ionic bond Covalent bond Van der Waals Bond Hydrogen Bonds © 2005 Pearson Education

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Ionic Bond Interaction between oppositely charged ionized atoms

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© 2005 Pearson Education Covalent Bond Interaction between charge distributions that are nearly spherically symmetric.

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© 2005 Pearson Education Van der Waal’s Bonds Van der Waal’s Bonds Interaction between the electric dipole moments of atoms or molecules Hydrogen Bonds a proton gets between two atoms, polarizing them and attracting them by means of the induced dipoles

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42.2 Molecular Spectra © 2005 Pearson Education

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rotational energy levels, diatomic molecule moment of inertia of a diatomic molecule © 2005 Pearson Education

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vibrational energy levels of a diatomic molecule © 2005 Pearson Education

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Energy level diagram for vibrational and rotational energy level of a diatomic molecules

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42.3 Structure of Solids © 2005 Pearson Education Crystalline solids Long-range order and a recurring pattern of atomic position that extends over many atoms Amorphous solids Short-range order and not a recurring pattern of atomic position

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© 2005 Pearson Education Crystal lattices Simple cubic fcc bcc hcp

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42.4 Energy Bands © 2005 Pearson Education Origin of energy bands in a solid

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© 2005 Pearson Education Three types of energy-band structure

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42.5 Free-Electron Model of Metals © 2005 Pearson Education Possible wave function: Energies of the states are

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density of states, free-electron model © 2005 Pearson Education

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Fermi-Dirac distribution © 2005 Pearson Education

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Example 42.7 For free electrons in a solid, at what energy is the probability that a particular state is occupied equal to a)0.01? ANS: © 2005 Pearson Education A state 4.6kT above the Fermi level is occupied only 1% of the time

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42.6 Semiconductors © 2005 Pearson Education

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N-type

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© 2005 Pearson Education P-type

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42.7 Semiconductor Devices © 2005 Pearson Education p-n junction

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© 2005 Pearson Education At equilibrium Under forward-bias

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© 2005 Pearson Education Under reverse-bias

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© 2005 Pearson Education Transistors A bipolar junction transistor includes 2 p-n junction in sandwich configuration

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The principal types of molecular bonds are ionic, covalent, van der Waals, and hydrogen bonds. In a diatomic molecule the rotational energy levels are given by Eq. (42.3), where I is the moment of inertia of the molecule and m r is its reduced mass. The vibrational energy levels are given by Eq. (42.7), where k’ is the effective force constant of the interatomic force. (See Examples 42.1 through 42.4) © 2005 Pearson Education

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Interatomic bonds in solids are of the same types as in molecules plus one additional type, the metallic bond. Associating the basis with each lattice point gives the crystal structure. (See Example 42.5)

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© 2005 Pearson Education When atoms are bound together in condensed matter, their outer energy levels spread out into bands. At absolute zero, insulators and conductors have a completely filled valence band separated by an energy gap from an empty conduction band. Conductors, including metals, have partially filled conduction bands. (See Example 42.6)

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In the free-electron model of the behavior of conductors, the electrons are treated as completely free particles within the conductor. In this model the density of states is given by Eq. (42.16). The probability that an energy state of energy E is occupied is given by the Fermi-Dirac distribution, Eq. (42.17), which is a consequence of the exclusion principle. In Eq. (42.17), E F is the Fermi energy. (See Examples 42.7 through 42.9) © 2005 Pearson Education

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A semiconductor has an energy gap of about 1 eV between its valence and conduction bands. Its electrical properties may be drastically changed by the addition of small concentrations of donor impurities, giving an n-type semiconductor, or acceptor impurities, giving a p-type semiconductor. (See Example 42.10)

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© 2005 Pearson Education Many semiconductor devices, including diodes, transistors, and integrated circuits, use one or more p-n junctions. The current-volt-age relation for an ideal p-n junction diode is given by Eq. (42.23). (See Example 42.11)

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END Visit: happyphysics.com For Physics Resources

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