Ch16_Part 2_complete_071811

Ch16_Part 2_complete_071811 - Why is water so awesome?...

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Why is water so awesome? (Near) universal solvent – The high polarity (and, therefore, hydrogen bonding power) of water means it can dissolve so many compounds – ionic compounds, polar, non- ionic compounds and even non-polar gases.
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Thermal properties – Water has a high heat capacity (higher than almost any liquid). High intermolecular forces mean water can absorb a lot of heat before it boils. This allows the earth to remain at a steady temperature. – Water has a high heat of vaporization which gives it enormous cooling power. Example: Adding 4 kJ of heat to 1000g of water causes the temperature to rise 1 °C, but only 2g of that water has to evaporate to keep the remaining 998g at a constant temperature. Why is water so awesome?
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Surface properties – High surface tension and high “capillarity” (both results of hydrogen bonding) are critical to plant life (land and aquatic). Why is water so awesome?
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Density of solid and liquid water – Because solid water (ice) is less dense than liquid water (as a result of hydrogen bonding), ice floats on water. This protects aquatic life, erodes rocks, but sometimes freezes your pipes… Why is water so awesome?
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Chapter #16 – Liquids and Solids 16.1) Intermolecular Forces 16.2) The Liquid State 16.3) An Introduction to Structures and Types of Solids 16.4) Structure and Bonding of Metals 16.5) Carbon and Silicon: Network Atomic Solids 16.6) Molecular Solids 16.7) Ionic Solids 16.8) Structures of Actual Ionic Solids 16.9) Lattice Defects 16.10) Vapor Pressure and Changes of State 16.11) Phase Diagrams
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What happens when substances freeze into solids? • Less thermal energy available • Less motion of the molecules • More ordered spatial properties Crystals (or Glasses)
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Properties of Crystals Unit Cell: The smallest repeating unit needed to describe the complete extended structure of a crystal (through repetition and translation).
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Figure 16.9 Some Common Crystal Lattices
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Figure 16.10 How do we know what crystals look like? x-ray diffraction Why x-rays? To satisfy the diffraction conditions, the wavelength of light needs to be comparable to the unit cell dimensions Ångstroms (10 -10 meters)
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Figure 16.11 Diffraction Conditions From trigonometry: n l = 2d sin q Key Point: Typical interatomic and intermolecular distances are d ≈ 1.0 to 20Å Typical x-ray wavelengths are l ≈ 0.01 to 10Å
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The X-ray Diffraction Experiment Crystal structure Molecular structure
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3 Types of Crystalline Solids Ionic Solids e.g. salts like NaCl Molecular Solids e.g. protein crystals, sucrose Atomic Solids e.g. all metals, Si, Carbon (diamond, graphite) Figure 16.12
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Physical properties of crystals Crystal structure Bonding forces Physical Properties melting point mechanical strength electrical properties Example: Copper and Diamond are both atomic solids, but they have very different physical properties: Copper: very soft, lower melting point (1083°C), excellent conductor Diamond: hardest known substance, higher m.p. (3500°C), insulator
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Ch16_Part 2_complete_071811 - Why is water so awesome?...

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