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Test 2 Study Guide

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Rutgers University

Test 2 Study Guide ctest21 Solids: 11.5 – 11.7 Types of solids 1. crystalline solids: long-range ordering (3D repeating pattern); homogeneous; sharp (small range) mp because they are arranged symmetrically (ex: ice, salt, gems) 2. amorphous solids: no regular repeating units; melt over a range of T (ex: glass, plastic, ceramic) SiO2(silica or quartz) can make quartz crystal or quartz sand (makes glass) Glass: transparent fusion product of inorganic materials that cooled to a rigid state w/o crystallizing Unit c: smallest part of a lattice that can be repeated to construct the full lattice In a 3D repeating pattern = crystal/crystalline lattice Corners = lattice points (atoms, molecules, ions) Angles + edges are characteristic/constant of the substance 3D unit c Primitive cubic: structural particles centered only at corners (d= 8 x 1/8 = 1) Body-centered cubic (bcc): 1 additional structural particle at center of cube (d=8 x 1/8 + 1=2) Face-centered cubic (fcc): additional structural particle at center of each face; no particle in center of cube (d=8 x 1/8 + 6 x ½ = 4) Density of a solid depends on number of atoms per unit c Corner atom: shared by 8 unit c Face atom: shared by 2 unit c Corner atoms don’t touch each other in bcc or fcc; each corner atom in bcc touches only the center atom; each corner atom in fcc touches center atom and face atoms Ionic Crystalline Structure: Ions pack as close as their ionic radii allow in order to maximize electrostatic interaction (and minimize internal E) of crystalline structure V(cation) < V(anion) For optimal electrostatic attraction: anions define the type of lattice; cations occupy geometrically well-defined 3D holes Cations occupy octahedral or tetrahedral holes in fcc lattices that anions form I- ions form a simple cubic crystalline network (ex: CsI) Network covalent solids: Lattice pts occupied by nonmetal atoms Atoms held tgther in huge molecules by a 3d network of covalent bonds Ex: silicates Ex: C allotropes (ex: graphite is C-planar; soft; good solid lubricant; electrical conductor parallel to layers; covalent bonds b/w C atoms, London forces b/w layers) (ex: diamond is C-tetrahedral; hard; more dense; does not conduct electricity) (ex: fullerene C60 buckyball; greatest V for least surface) (ex: nanotube: sheet of graphite rolled into tube capped with half a buckyball) Allotrpe: diff form of same element in same physical state, at same T and P Metals, semiconductors, and insulators: 11.8 – 11.10 Metallic solids: Lattice pts occupied by metal atoms Held tgthr by metallic bonds Metallic bonding: nondirectional attraction (mobile sea of valence e-) Metallic properties: - high electrical/thermal conductivity - ductile; malleable - luster - insoluble in H2O, but some can react w/ H2O E-band theory: 1. as atoms are added to crystal 2. N of orbitals available to merge into bands increases 3. the e- occupy the lowest E lvls available Only valence e- determine metallic properties b/c are more mobile Conduction band: band containing empty orbitals of higher E Valence band: band containing valence e- (extra E from heat, photons, electric field, etc) e- move from valence band to conduction band Based on size of gap b/w valence and conduction bands: Large diff: insulators Overlapping band: conductors Small E diff: semiconductors Silicon semiconductors Doping: ctrlled addition of tiny amt of another element (dopant) to increase conductivity of silicon crystals Perfect crystal: all atoms are alike n-type (negative): in an Si crystal doped w/ an As atom, an extra valence e- is available to conduct electricity; more e- to conduct; doping w/ elements from main group V p-type (positive): in an Si crystal doped w/ a B atom, a hole exists that a neighboring e- can move into, thus causing electrical conductivity; less e-, but extra holes so more e- are mobile; doping from elements from main group III Holes: fewer e- as compared to pure Si, so it’s like the doped Si gets a positive charge Actual charge carrier is always e- n-type + p-type = electrical field formed w/I cell = solar cell Solutions: 5.6 Solution: homogenous mixture of substances Solvent: component in greatest amt Solute: all other soluble components in solvent Types of solution Gas in gas: air Gas in l: soda G in s: h2(g) in Pd(s) L in l: motor oil, vinegar S in l: ocean water; sugar-water S in s: bronze; 14K gold Concentration: amt of constituent in mixture 1. percent concentration (%) % (w/w): mass solute/mass solution x100 % (w/v): mass solute/V solution x100 % (v/v): V solute/V solution x100 2. molarity (M) M=moles solute/V solution (mol/L) 3. molality (m): the only concentration defined w/ respect to pure solvent rather than to solution m=moles solute/mass(solvent) (kg) 4. mole fraction (Xa) Xa=moles solute/moles solution Chemical kinetics: 13.1 Chemical kinetics: study of reaction rates Reaction rate: change in concentration of a reactant or product per unit of time Instantaneous rate calculated at beginning of reaction b/c that’s when reaction is at max speed Reaction rate: aA+bBcC+dD Rate (mol/Ls) = -1/a x change [A]/change t = -1/b x change[B]/change t = +1/c x change [C]/change t = +1/d change [D]/change t Average rate: change in
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