Title: Solids
1Solids
- We can think of solids as falling into two
groups - Crystallineparticles are in highly ordered
arrangement.
2Solids
- Amorphousno particular order in the arrangement
of particles.
3Attractions in Ionic Crystals
- In ionic crystals, ions pack themselves so as to
maximize the attractions and minimize repulsions
between the ions.
4Crystalline Solids
- Because of the order in a crystal, we can focus
on the repeating pattern of arrangement called
the unit cell.
5Crystalline Solids
- There are several types of basic arrangements in
crystals, such as the ones shown above.
6Crystalline Solids
- We can determine the empirical formula of an
ionic solid by determining how many ions of each
element fall within the unit cell.
7Ionic Solids
- What are the empirical formulas for these
compounds? - (a) Green chlorine Gray cesium
- (b) Yellow sulfur Gray zinc
- (c) Green calcium Gray fluorine
(a)
(b)
(c)
CsCl
ZnS
CaF2
8Types of Bonding in Crystalline Solids
9Covalent-Network andMolecular Solids
- Diamonds are an example of a covalent-network
solid in which atoms are covalently bonded to
each other. - They tend to be hard and have high melting points.
10Covalent-Network andMolecular Solids
- Graphite is an example of a molecular solid in
which atoms are held together with van der Waals
forces. - They tend to be softer and have lower melting
points.
11Metallic Solids
- Metals are not covalently bonded, but the
attractions between atoms are too strong to be
van der Waals forces. - In metals, valence electrons are delocalized
throughout the solid.
12Metallic Bonding
"SEA OF MOBILE VALENCE ELECTRONS" The animation
you are looking at attempts to help you
understand the nature of a metal bond. The gray
spheres represent metal cations (positively
charged ions), and the red moving spheres
represent electrons. Metals have low ionization
energies, thus they do not have a tight hold on
their valence electrons. These outer electrons
easily move around, as they do not "belong" to
any one atom, but are part of the whole metal
crystal. The negatively charged electrons act as
a "cement" that hold the positively charged metal
ions in their relatively fixed positions.
13The fact that the electrons flow easily helps to
explain some of the characteristics of metals -
Metals are good conductors of heat and
electricity. This is directly due to the mobility
of the electrons. - The "cement" effect of the
electrons determines the hardness of the metal.
Some metals are harder than others the strength
of the "cement" varies from metal to metal. -
Metals are lustrous. This is due to the uniform
way that the valence electrons of the metal
absorb and re-emit light energy. - Metals are
malleable (can be flattened) and ductile (can be
drawn into wires) because of the way the metal
cations and electrons can "flow" around each
other, without breaking the crystal
structure. Metallic bonds are best characterized
by the phrase "a sea of electrons"
14- Metallic Bonding
- atoms in metals are packed very closely in an
orderly arrangement -
- each atom loses its valence electrons to become a
positive ion -
15Phase Diagrams Equilibrium can exist not only
between the liquid and vapor phase of a substance
but also between the solid and liquid phases, and
the solid and gas phases of a substance. A phase
diagram is a graphical way to depict the effects
of pressure and temperature on the phase of a
substance
16Phase Diagrams
- Phase diagrams display the state of a substance
at various pressures and temperatures and the
places where equilibria exist between phases.
17Phase Diagrams
- The AB line is the liquid-vapor interface.
- It starts at the triple point (A), the point at
which all three states are in equilibrium.
18Phase Diagrams
- It ends at the critical point (B) above this
critical temperature and critical pressure the
liquid and vapor are indistinguishable from each
other.
19Phase Diagrams
- Each point along this line is the boiling point
of the substance at that pressure.
20Phase Diagrams
- The AD line is the interface between liquid and
solid. - The melting point at each pressure can be found
along this line.
21Phase Diagrams
- Below A the substance cannot exist in the liquid
state. - Along the AC line the solid and gas phases are in
equilibrium the sublimation point at each
pressure is along this line.
22Phase Diagram of Water
- Note the high critical temperature and critical
pressure - These are due to the strong van der Waals forces
between water molecules.
23Phase Diagram of Water
- The slope of the solidliquid line is negative.
- This means that as the pressure is increased at a
temperature just below the melting point, water
goes from a solid to a liquid.
24Phase Diagram of Carbon Dioxide
- Carbon dioxide cannot exist in the liquid state
at pressures below 5.11 atm CO2 sublimes at
normal pressures.
25Phase Diagram of Carbon Dioxide
- The low critical temperature and critical
pressure for CO2 make supercritical CO2 a good
solvent for extracting nonpolar substances (such
as caffeine).