Covalent bonds everywhere high melting point 106

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Covalent bonds everywhere high melting point
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10.6: Lattice Structures in Crystalline Solids Structures defined by 1. Size and shape of unit cell 2. Location of atoms within unit cell Lattice structures: formation of crystalline solids (unit cells) – Lattice energy : energy required to separate 1 mole of a crystalline ionic solid into its gaseous ions o Stronger attraction between ions, more energy needed, higher lattice energy Larger charge, stronger attraction, greater lattice energy Longer distance, smaller lattice energy Higher lattice energy, higher melting point coordination number : # of other atoms that each atom is in direct contact with Cubic unit cell – molecular solid Simple (primitive) cubic o 1 atom o Coordination # = 6 o Packing efficiency = 52% Body-centered cubic o 2 atoms o Coordination # = 8 o Packing efficiency = 68% Face-centered cubic o 4 atoms o Coordination # = 12 o Packing efficiency = 74%
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Solutions and Colloids (Ch. 11) Solutions : homogenous mixtures made of 2+ substances Solute : substances being dissolved Solvent : substance doing dissolving o Usually largest amt. and liquid 3 physical states o Solid solution – metal alloys o Gas solution – air o Liquid solution – aqueous solution Concentration units Molarity : Weight (mass) percent: Volume percent : Molality: Mole fraction: Part per million/billion /
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11.1: The dissolution Process Traits of solutions 1. Homogenous 2. Physical state of solution is typically the same as the solvent, but properties of solution and pure solvent can be quite diff 3. Dissolved solute will not settle out or separate from solution, even if it is heavier than the solvent 4. Components of solution are dispersed and consist of mixture of separate molecules, atoms, and/or ions Dissolution process = spontaneous – process occurs under specified conditions without requirement of energy from some external source Formation of solutions Solute-solute interaction (∆H1) o IMFs overcome energy absorbed Solvent-solvent interaction (∆H2) o IMFs overcome energy absorbed Solute-solvent interaction (solvation) (∆Hsolv) o Attractive forces established energy released Conditions which favor spontaneous formation of solution 1. Decrease internal energy of system ( decrease energy/exothermic, ∆H<0 ) a. If 2 substances have very similar IMFs, highly exothermic, likely to be soluble in 1 another b. “like dissolves like” 2. Increase in disorder of system ( increasing entropy, ∆S>0 )
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11.2: Electrolytes Electrolytes : substances that dissolve in water and undergo a physical or chemical change to produce ions Strong electrolytes: essentially 100% of the dissolved substances generates ions Weak electrolytes: only relatively small fraction of dissolved substance generates ions To conduct electricity, a solution must contain ions Water and other polar molecules attracted to ions (water surrounds and solvates separated ions dissociation ) Nonelectrolytes : substances that do not produce ions when dissolved in water Solubility of ionic compounds (metal + nonmetal)
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