Zumdahl Zumdahl DeCoste

Zumdahl Zumdahl DeCoste
World of CHEMISTRY

Figure 14.1: Representations of the gas, liquid, and solid states.
Solid and liquid states more similar than liquid and gaseous states Copyright© by Houghton Mifflin Company. All rights reserved.

Intermolecular Forces
Explain why water is liquid at normal temperature and pressure Forces that occur between molecules Dipole-dipole attraction 1% as strong as bonds Weaken as distance increases Hydrogen bonding (type of dipole-dipole force) Hydrogen bound to highly electronegative atom London dispersion forces Exist in noble gases and nonpolar molecules Temporary dipole moments form producing attraction Intramolecular forces: forces within molecule itself (bonds) Copyright© by Houghton Mifflin Company. All rights reserved.

Figure 14.4: Polar water molecules.
Copyright© by Houghton Mifflin Company. All rights reserved.

Figure 14.4: Hydrogen bonding among water molecules.

Figure 14.5: The boiling points of covalent hydrides.

Figure 14.6: Atoms with spherical electron probability.

14.6: The atom on the left develops an instantaneous dipole.

Figure 14.6: Instantaneous dipole on A induces a dipole on B.

Water and Its Phase Changes
Normal boiling point of water = 100°C at pressure = 1 atm Normal freezing point of water = 0°C at pressure = 1 atm Copyright© by Houghton Mifflin Company. All rights reserved.

Energy Requirements for Change of State
Extra energy needed to change state (solid to liquid, liquid to vapor) – need to overcome intermolecular forces Molar heat of fusion (water) = 6.02 kJ/mol Molar heat of vaporization = 40.6 kJ/mol Copyright© by Houghton Mifflin Company. All rights reserved.

Evaporation and Vapor Pressure
Evaporation/vaporization: requires energy to overcome intermolecular forces Endothermic process Condensation: vapor molecules form a liquid Eventually (in closed container) the rate of vaporization = rate of condensation; system is in equilibrium Molecules are still vaporizing/condensing, but there is no net change because they balance each other out Copyright© by Houghton Mifflin Company. All rights reserved.

Figure 14.9: Microscopic view of a liquid near its surface.

Figure 14.10: Behavior of a liquid in a closed container.

Figure 14.11: (a) Measuring vapor of a liquid by using a simple barometer (b) The water vapor pushed the mercury level down (c) Diethyl ether shows a higher vapor pressure than water. Copyright© by Houghton Mifflin Company. All rights reserved.

Vapor Pressure Liquids with high vapor pressures are said to be volatile: they evaporate rapidly Determined by intermolecular forces Large intermolecular forces = low vapor pressure Copyright© by Houghton Mifflin Company. All rights reserved.

Figure 14.12: Water rapidly boiling on a stove.
Bubbles form on interior of liquid, then rise to surface and POP! Copyright© by Houghton Mifflin Company. All rights reserved.

Figure 14.13: Bubble expands as H2O molecules enter.
Vapor pressure must equal atmospheric pressure for boiling to occur Bubbles must have enough energy to sustain pressure in bubble Boiling point decreases with altitude because atmospheric pressure is less Copyright© by Houghton Mifflin Company. All rights reserved.

Types of Solids Crystalline solids: have regular arrangements of their components highly ordered arrangement produces beautiful, regularly shaped crystals Copyright© by Houghton Mifflin Company. All rights reserved.

Figure 14.15: Sodium and chloride ions.

Figure 14.17: The classes of crystalline solids.

Figure 14.18: A molecular solid.

Figure 14.19: The packing of Cl¯ and Na+ ions in solid sodium chloride. Ionic Solids: Stable High melting points Held together by strong forces Spheres packed together as efficiently as possible Copyright© by Houghton Mifflin Company. All rights reserved.

Figure 14.21: A representation of part of the structure of solid phosphorus. Molecular Solids: Fundamental particle is a molecule Relatively low melting points – weak intermolecular forces Either dipole-dipole or London forces Bonds between atoms stronger than bonds between molecules Copyright© by Houghton Mifflin Company. All rights reserved.

Atomic Solids Properties vary greatly because of different ways fundamental particles interact with each other Group 8: low melting points, filled shells, weak London dispersion forces Diamond: one of hardest substances known, extremely high melting point, very strong covalent carbon-carbon bonds Copyright© by Houghton Mifflin Company. All rights reserved.

Bonding in Metals Shape can be changed easily, but durable with high melting points Bonding is strong but nondirectional Electron sea model: array of metal atoms in a “sea” of valence electrons that are shared among the atoms Electrons can conduct heat and electricity and atoms can move easily Copyright© by Houghton Mifflin Company. All rights reserved.

Alloys Alloy: substance that contains a mixture of elements and has metallic properties Because of nature of metallic crystal, other substances can be easily introduced Copyright© by Houghton Mifflin Company. All rights reserved.

Figure 14.22: Molecular representation of brass.
Substitutional alloy: some of the host metal atoms are replaced by other metal atoms of similar sizes Copyright© by Houghton Mifflin Company. All rights reserved.

Figure 14.22: Molecular representation of steel.
Interstitial alloy: holes among the closely packed metal atoms are occupied by atoms much smaller than the host atoms Copyright© by Houghton Mifflin Company. All rights reserved.

Zumdahl Zumdahl DeCoste

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