AP Chapter 10 - They are similar to each other Different...

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1 Liquids and solids They are similar to each other r Different than gases. r They are incompressible. r Their density doesn’t change much with temperature. r These similarities are due • to the molecules staying close together in solids and liquids • and far apart in gases r What holds them close together? Intermolecular forces r Inside molecules (intramolecular) the atoms are bonded to each other. r Intermolecular refers to the forces between the molecules. r Holds the molecules together in the condensed states. Intermolecular forces r Strong • covalent bonding • ionic bonding r Weak • Dipole dipole • London dispersion forces r During phase changes the molecules stay intact. r Energy used to overcome forces. Dipole - Dipole r Remember where the polar definition came from? r Molecules line up in the presence of a electric field. The opposite ends of the dipole can attract each other so the molecules stay close together. r 1% as strong as covalent bonds r Weaker with greater distance. r Small role in gases. + - + - + -
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2 Hydrogen Bonding r Especially strong dipole-dipole forces when H is attached to F, O, or N r These three because- • They have high electronegativity. • They are small enough to get close. r Effects boiling point. CH 4 SiH 4 GeH 4 SnH 4 PH 3 NH 3 SbH 3 AsH 3 H 2 O H 2 S H 2 Se H 2 Te HF HI HBr HCl Boiling Points 0ºC 100 -100 200 Water δ + δ - δ + Each water molecule can make up to four H-bonds London Dispersion Forces r Non - polar molecules also exert forces on each other. r Otherwise, no solids or liquids. r Electrons are not evenly distributed at every instant in time. r Have an instantaneous dipole. r Induces a dipole in the atom next to it. r Induced dipole- induced dipole interaction. Example H H H H δ + δ - δ + δ- London Dispersion Forces r Weak, short lived. r Lasts longer at low temperature. r Eventually long enough to make liquids. r More electrons, more polarizable. r Bigger molecules, higher melting and boiling points. r Weaker than other forces.
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3 Van der Waal’s forces r London dispersion forces and Dipole interactions r Order of increasing strength • LDF • Dipole • H-bond • Real bonds Liquids r Many of the properties due to internal attraction of atoms. • Beading • Surface tension • Capillary action • Viscosity r Stronger intermolecular forces cause each of these to increase. Surface tension r Molecules in the middle are attracted in all directions. r Molecules at the the top are only pulled inside. r Minimizes surface area. Capillary Action r Liquids spontaneously rise in a narrow tube. r Intermolecular forces are cohesive, connecting like things. r
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This note was uploaded on 09/28/2009 for the course CHEM 102 taught by Professor Freeman during the Spring '08 term at South Carolina.

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AP Chapter 10 - They are similar to each other Different...

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