Chapter 12 Learning Objectives: Solids and Modern Materials - Bonding PDF

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This is a summary of the lecture notes and learning objectives related to Solids and Modern Materials - specifically Bonding
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Chapter 12: Bonding 12.4 Metallic bonding O. Describe the electron-sea model of metallic bonding. 1. A model for behavior of electrons in metals. Electrons are confined to metal by electrostatic cations uniformly distributed in structure. P. Use the molecular-orbital model of metallic bonding to predict the electronic band structure of metals. 1. Molecular-orbital model a. Atomic orbitals combine to make molecular orbitals that can extend over the entire molecule b. A molecular orbital can contain 0, 1, or 2 electrons c. The number of molecular orbitals in a molecule equals the number of atomic orbitals that combine to form molecular orbitals d. Adding electrons to bonding molecular orbitals strengthens bonding while adding electrons to to antibonding molecular orbitals weakens bonding. 2. Band a. An array of closely spaced molecular orbitals occupying a continuous range of energy 3. Band structure a. The electronic structure of a bulk solid

12.5 Ionic solids Q. Explain how ionic radii and empirical formulas relate to observed structures of ionic solids. 1. Radii a. When cation and anions are similar in size i. a large coordination number is favored b. When the relative size of cation decreases i. Coordination number drops from 8 to 6 c. Cation decreases more in size i. Coordination drops from 6 to 4

2. Stoichiometry a. As cation/anion ratio goes down, there are fewer cations to surround each anion -- anion coordination number reduces b. (Number of cations per formula unit/Number of anions per formula unit) = (anion coordination number/cation coordination number) c. NaCl -- both have coordination numbers of 6 d. MgF2 -- rutile structure -- cation coordination number = 6; anion = 3

12.6 Molecular solids R. Interpret melting point and boiling point data of molecular solids in terms of intermolecular forces and crystalline packing. 1. Melting and boiling point a. Stronger IMF = higher mp b. Better packing = higher mp 12.7 Covalent-network solids S. Define the terms valence band, conduction band, band gap, holes (the chemical meaning), semiconductor, and insulator.

1. Valence Band a. A band of closely spaced bonding molecular orbitals that is essentially fully occupied electrons 2. Conduction Band a. A band of unoccupied antibonding molecular orbitals lying higher in energy than the occupied valence band and distinctly separate from it. 3. Band gap a. The energy gap between a fully occupied valence band and an empty conduction band. 4. Doping a. The process of adding controlled amounts of impurity atoms to a material. Adding P to Si (P has more electrons, n-type semiconductor) 5. Holes a. A vacancy in the valence band created by doping 6. Semiconductor a. A material that has electrical conductivity between that of a metal and that of an insulator 7. Insulator a. Material that does not conduct electricity. T. Explain how band theory accounts for the different conductivities of conductors versus semiconductors. 1. No band gap = conductor 2. Small bandgap = semiconductor 3. Large band gap = insulator U. Describe how valence bands and conduction bands result from the valence atomic orbitals of the atoms in a solid. 1. Conduction band a. No electrons 2. Valence bad a. Filled with electrons V. Describe the band structure of p- and n-type semiconductors. 1. P-type semiconductor a. Adding material with fewer valence electrons b. Positive holes in the material has increased 2. N-type semiconductor a. Adding material with more valence electrons b. Number of negatively charged electrons in the material has increased W. Explain how n-type and p-type doping can be used to control the conductivity of semiconductors. 1. Put them together 2. Alone

a. n-type jump within conduction band b. p-type jump within valence band c. Both together -- moves from n-cond to p-vals i. Fill the holes X. Calculate the wavelength that corresponds to band gap energy in Joules. 1. E = hc/lambda 12.8 Polymers Y. Recognize the features of a molecule that allow it to form a polymer. 1. Polymers a. Large molecule with long chains of atoms where the atoms within a given chain are connected by covalent bonds and adjacent chains are held to one another largely by IMF 2. Monomors a. Molecules with low molecular weights, which can be joined together to form a polymer. 3. Addition polymerization a. Need double bonds that can break to link to monomers to left + right 4. Condensation polymer a. C double bond O and ndext to it should be an exoygen or nitrogen. b. CONDENSATION Z. Describe how addition and condensation polymers form. 1. Addition polymerization a. A chemical reaction in which monomers are linked to form polymers with no by product 2. Condensation polymer a. Monomers linked to form polymers with the elimination of simple molecules like water AA. Given a molecular structure, determine whether a monomer would form an addition or condensation polymer. 5. Addition polymerization a. Need double bonds that can break to link to monomers to left + right b. Carbon backbone with random maybe outjuts 6. Condensation polymer a. C double bond O and next to it should be an oxygen or nitrogen. b. CONDENSATION c. Polyesters i. -CO2H and COH d. Polyamides i. -CO2H + CNH BB. Explain how interactions between polymer chains impact the physical

properties of polymers. 1. Polymers = usually amorphous 2. Higher crystallinity (IMF) a. Higher MP, higher density, stiffer + stronger polymers CC. Draw an abbreviated synthetic polymer structure based on monomer structures. DD. Identify the monomer(s) given a polymer structure. Chains are not rigid; readily flexible 1. Crystallinity a. A measure of the extent of short-range ordering in a polymer were chains line up in regular arrays. 12.9 Nanomaterials EE. Describe how the properties of nanomaterials, such as band gap energy, change as the size of the crystals decrease to the nano-length scale (as discussed in case study for topic 5) 1. Nanomaterial a. A solid whose dimensions range from 1 to 100 nm and whose properties differ from those of a bulk material with the same composition. Difference between molecular solids and covalent-network solids? Just by formula 1. Cov net Metallic + o2 or n2 2. Molecule a. A full, whole molecule...