chapter 14 liquids & solids chemistry 101. introduction attractive forces kinetic energy keeps...
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Chapter 14
Liquids & Solids
Chemistry 101
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Introduction
Attractive forces Kinetic energy
Keeps molecules apartBrings molecules together
Physical sate of matter depends on:
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Introduction
Gas High kinetic energy (move fast)
Low attractive forces
Liquid Medium kinetic energy (move slow)
medium attractive forces
Solid Low kinetic energy (move slower)
High attractive forces
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Melting
Boiling
Physical Changes
Change of states
Arrangement of density (normally): Solids > Liquids > Gases
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Intermolecular forces
London dispersion forces
Dipole-dipole interaction
Hydrogen bonding
ionic bondcovalent bond<
Intramolecular forces
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London dispersion forces
Attractive forces between all molecules
Only forces between nonpolar covalent molecules
2+
No PolarityOriginal Temporary
Dipole
δ- δ+
+2+
HeHe
Original Temporary Dipole
Induced Temporary Dipole
__ _ _
He He
2+_ ___ 2+
δ- δ+He
__ 2+
δ- δ+He
__ 2+
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London dispersion forces
T ↓ Kinetic energy ↓Move slower
Attractive forcesbecome more important liquid
He: T = -240°C (1 atm) → liquid
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Dipole-Dipole Interactions
Attractive force between two polar molecules.
stronger than London dispersion forces
boiling point ↑
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Hydrogen Bonds
Stronger than dipole-dipole interactions & London dispersion forces
surface tensionHigh boiling point
H2O
H O
H
H
O
H
- +
hydrogenbond
hydrogenbond
- +
(a) (b) (c)
Between H bonded to O, N, or F (high electronegativity) → δ+and a nearby O, N, or F → δ-
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Hydrogen bonding
CH3COOH
Acetic acidδ-
δ+
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H-bonding in our body
DNA
H-bond
Protein (α-helix)
H-bond
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Evaporation
equilibrium
Vapor pressure: the pressure of a gas in equilibrium with its liquid form in a closed container.
Boiling point: the temperature at which the vapor pressure of a liquid is equal to the atmospheric pressure.
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Evaporation
vacuum
670 mm
Measuring vapor pressure of liquids
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Evaporation
normal boiling point: the temperature at which a liquid boils under a pressure of 1.00 atm.
760 mm Hg
H2O
CH3OH
Die
thyl
eth
er
1 atm. =
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Evaporation
Factors that affect boiling point:
1. Intermolecular forces:
London dispersion forces < Dipole-Dipole interactions < Hydrogen bonds
3. Molecular shape: With the same molecular weight.
linear CH3-CH2-CH2-CH2-CH3 > spherical CH3-C- CH3
_
_
CH3
CH3
2. Number of sites for intermolecular interactions (surface area):
Larger surface (more electrons) more sites for London b.p.
CH3-CH2-CH2-CH2-CH3 > CH3-CH2-CH3
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Solid
Crystalline solid (Network solids)
Amorphous solid
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Crystalline solids (Network solids)
Crystalline solid
Ionic solids: Consist of ions (metal-nonmetal) NaCl
Stable - High melting points
Molecular solids: Consist of molecules. Sugar, Ice
Lower melting points
London dispersion forces, Dipole-Dipole interaction, H-Bond
Atomic solids: Consist of atoms. Diamond, Graphite, Metals
Different melting points (because of forces between atoms).
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Bonding in metals
Electron Sea Model
Valance electrons are shared among the atoms in a nondirectional way.
Metals conduct heat and electricity.
They are malleable and ductile.
We can make alloys.
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Alloys
Substitutional alloy:
Interstitial alloy:
Some of the host metal atoms are replaced by other metal atoms of similar sizes.
Brass: (Copper, Zinc)
Some of the holes among the metal atoms are occupied by atoms much smaller.
Steel: (Iron, Carbon)
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Solid
Fusion (melting): change phase from solid to liquid.
Sublimation: change phase from solid directly into the vapor.
Dry ice (solid CO2)
Solidification (Crystallization): change phase from liquid to solid.
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Heating/Cooling Curve
Heat added (cal)
during the phase changes, the temperature stays constant.
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Molar heat of fusion: Energy required to melt 1 mol of a solid.
(For ice: 6.02 kJ/mol)
Molar heat of vaporization: Energy required to vaporize 1 mol of liquid.
(For water: 40.6 kJ/mol)
We need more energy for vaporization than fusion: Why?
To separate molecules enough to form a gas all of the intermolecular forces must be overcome.
Heat and physical state
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Phase diagram