Liquids. Molecules at interfaces behave differently than those in the interior. Molecules at surface experience a net INWARD force of attraction. This leads to SURFACE TENSION — the energy req’d to break through the surface. Surface Tension.
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Molecules at interfaces behave differently than those in the interior.
Molecules at surface experience a net INWARD force of attraction.
This leads to SURFACE TENSION — the energy req’d to break through the surface.
SURFACE TENSION also leads to spherical liquid droplets (shape of minimum surface).
Cohesive forces against the force of gravity
Movement of water up a piece of paper depends on H-bonds between H2O and the OH groups of the cellulose in the paper.
Problem : Search for applications of capillary action
in nature (plants) and in the lab (chromatography)
VISCOSITYis the tendency or resistance of liquids to flow.
Do you expect the viscosity of glycerol to be larger or
smaller than the viscosity of ethanol ?
The resistance to flow results from several factors, including
intermolecular interactions, molecular shape and size.
Solid-state chemistry is one of the booming areas of science, leading
to the development of interesting new materials.
TYPE Composition BINDING FORCES
Ionic NaCl, CaF2, ZnS Ion-ion
Metallic Na, Fe Metallic
Molecular Ice, I2 Dipole Ind. dipole
Network Diamond Extended Graphite covalent
Networks with no
A comparison of diamond (pure carbon) with silicon.
1. Molecules, atoms or ions locked into a CRYSTAL LATTICE
2. Particles are CLOSE together
3. STRONG IM forces
ZnS, zinc sulfide
Simple cubic (SC)
Body-centered cubic (BCC)
Face-centered cubic (FCC)
1 atom/unit cell
2 atoms/unit cell
4 atoms/unit cell
Assume atoms are hard spheres and that crystals are built by PACKING of these spheres as efficiently as possible.
Unit Cell Type Net Number Atoms
Atom shared in corner
--> 1/8 inside each unit cell
Atom shared in face
--> 1/2 inside each unit cell
CsCl has a SC lattice of Cs+ ions with Cl- in the center.
1 unit cell has 1 Cl- ion plus
(8 corners)(1/8 Cs+ per corner)
= 1 net Cs+ ion.
Salts with formula MX can have SC structure — but not salts with formula MX2 or M2X
Either arrangement leads to formula of 1 Cs+ and 1 Cl- per unit cell
Many common salts have FCC arrangements of anions with cations in OCTAHEDRAL HOLES — e.g., salts such as CA = NaCl
• FCC lattice of anions ----> 4 A-/unit cell
• C+ in octahedral holes ---> 1 C+ at center
+ [12 edges • 1/4 C+ per edge]
= 4 C+ per unit cell
Lines connect all conditions of T and P where EQUILIBRIUM exists between the phases on either side of the line.
Normal boil point 100 760
Normal freeze point 0 760
Triple point 0.0098 4.58
In any system, if you increase P the DENSITYwill go up.
Therefore — as P goes up, equilibrium favors phase with the larger density (or SMALLERvolume/gram).
Liquid H2OSolid H2O
Density 1 g/cm3 0.917 g/cm3
cm3/gram 1 1.09
Raising the pressure at constant T causes water to melt.
The NEGATIVE SLOPE of the S/L line is unique to H2O. Almost everything else has positive slope.
At P < 4.58 mmHg and T < 0.0098 ˚C
solid H2O can go directly to vapor. This process is called SUBLIMATION
This is how a frost-free refrigerator works.