12 -- Part 4: Intermolecular Forces: Liquids and Solids
A feature not shown here is the curve of a phase change.
Applying the fusion curve OD to the right at pressure above the critical point increases the density of the supercritical temperatures above the critical fluid.
The path was traced by the small arrows.
No amount of pressure can liquefy a supercritical fluid.
The path of dots starts with a low density gas above the critical temperature.
A supercritical fluid is created when the pressure is increased.
If the pressure is greater than the critical pressure, we can get a liquid.
The sample is still in the liquid phase.
We went from a gas to a liquid without observing a liquid-gas interface.
The only way to observe the interface is to cross the phase boundary.
We can observe the liquid-vapor interface by lowering the pressure on the liquid to a point on the vapor pressure curve.
The mole fraction is the ratio of the total gas pressure to the vapor pressure.
The density of the SCF is high and approaches that of a liquid in a gas that is above its critical pressure and temperature.
Molecules in supercritical fluids can exert strong attractive forces on the molecule of a liquid or solid solute.
It is possible to vary the pressure of an SCF.
Carbon dioxide can be made to behave like many different solvents.
Until recently, the main method of decaffeinated coffee was to extract "naturally" decaffeinated the caffeine with a solvent.
This solvent coffee is objectionable because it is hazardous in the workplace and difficult to remove from the coffee.
CO fluid CO2 is used as a solvent.
In one process, green coffee beans are brought into contact with CO in order to get rid of the caffeine in green 2.
The coffee has less caffeine than its coffee beans.
The beans are roasted and sold at a rate of 1% to 3%.
The CO2 is reduced and recycled.
There is a phase diagram for water Point O.
The significance of the broken straight lines is discussed in the text.
If ice did not float, behave this way.
We don't fill ice with ice that would observe the melting behavior of ice because large changes in pressure are required.
Never melt is an example that has been given.
The majority of them are from ice-skating.
The skater skims along on a thin film of liquid water after the pressure of the skate blades melt the ice, more dense than their liquid.
Water is unlikely because the pressure of the blades doesn't suit us.
Ordinary ice is called ice I.
The other forms are only found at high pressures.
Polymorphism is more of a rule than an exception.
The equilibrium pressure to H2O is -22.0 degC and 2045 atm.
The temperature with ice VI, ice VII, and liquid water is 21,700 atm.
There is a small difference between these terms.
Liquid water can be described as a two-phase mixture.
The liquid is one phase and the gas is the other.
The phases are the same as the states of matter present.
The polymorphic forms of ice I and ice III are in the solid state.
A mixture of two or more components may have different phases in the liquid state as well as in the solid state.
One is a saturated solution of triethylamine in water and the other is a saturated solution of water in triethylamine.
There are six common names assigned to phase transitions.
There are two generalizations about the changes that occur when crossing a two-phase equilibrium curve.
Because ice is less dense, it has a positive slope.
Solids with a higher density than H2O(l) are more likely to have a fusion curve than the corresponding liquid.
The system is a mixture of establish the confining both phases.
The system is in that phase.
As the system moves from one phase to labeled P, Q, and R in another at the coexistence lines, remember the conditions at the points that are labeled P, Q, and R. Until all of one phase is H O(g) from point P to Q is converted to another, the transition ture is constant.
The pressure can be solved at constant temperature.
As ice is converted to liquid, the temperature remains constant.
The melting begins here.
Liquids are not very compressible after melting.
Phase diagrams can be used to understand the different phases of matter.
In the remainder of the chapter, we focus on the elements.
There are two major themes that will be followed in our discussion.
The bonding forces that hold the solid together are discussed in this section.
These forces contribute to the formation of orderly packing arrangements.
We will look at the geometries of some common packing arrangements in the next section.
In this section, we focus on solids that are held together by cova lent or ionic bonding forces.
Solids can be held together by intermolecular forces or metallic bonding forces.
The physical properties of a solid can be influenced by the nature of the bonding forces.
Solids held together by covalent or ionic bonding forces have higher melting points than those held together by intermolecular forces.
The crystal is held together by strong forces.
Consider two forms of pure carbon--diamond and graphite.
Diamond Figure 12-32 shows how carbon atoms can bond in a large array or crystal.
The Lewis structure suggests that the bonding scheme involves increasing numbers of C atoms leading to a giant molecule.
It doesn't give any insight into the structure of the molecule.
Each atom has a bond to four others.
The strongest of all the contributing forces have been listed.
A nonplanar hexagonal arrangement of carbon atoms is also seen when viewed from a certain direction.
If half the carbon atoms in this structure are replaced with Silicon atoms, the resulting structure is that of Silicon carbide.
The use of diamond and Silicon carbide as abrasives is due to their hard nature.
Diamonds are the hardest substance known.
covalent bonds must be broken in diamond or Silicon carbide crystals.
These two materials are non-conductors of electricity and do not melt, except at very high temperatures.
The properties of diamond are very different from those of carbon atoms.
Bonding involves the orbital set.
A central atom to the corners.
Each carbon atom forms strong bonds with three neighboring carbon atoms in the same plane, giving rise to layers of carbon atoms in a hexagonal arrangement.
Intermolecular forces between layers are weaker than bonding within layers.
Through bond distances, we can see this.
The C bond distance between layers is 335 pm.
Its crystal structure gives it some unique properties.
The layers can glide over one another because of the weak bonding between them.
It's a good lubricant if you use it in an oil suspension or in dry form.
If a mild pressure is applied to a piece ofGraphite, the layers ofGraphite are removed.
An important use of graphite is as a conductor of electricity in batteries and in industrial ysis.
Diamond is not an electrical conductor because all of its electrons are made of carbon.
The first of what is now known to be an extensive series of allotropes electodes to complete the carbon was discovered in 1985.
Experiments designed to mimic conditions.
The beaker contains a found near red-giant stars, a number of carbon-containing molecules were solution of ion that carry the discovered and characterized through mass spectroscopy.
The peak current is between the pencil electrodes.
It was a challenge to come up with a structure for this molecule.
The 142 pm molecule with 60 carbon atoms could not be accounted for by the diamond- or graphite-type structures.
335 pm a carbon atom is present at each of the 60 vertices of the threedimensional figure.
The figure is similar to a soccer ball and certain domes.
Since 1985, many other fullerenes have been discovered.
Several thousand fullerene compounds have been prepared.
A graphene sheet is a two-dimensional array of hexagonal rings of carbon atoms.
Chicken wire is an analogous structure.
Imagine cutting a piece of chicken wire and rolling the sheet of Graphene into a cylinder.
Half of a fullerene is needed to cap each end of the cylindrical Graphene sheet.
Their lengths can be several nanometers or more.
The promise of some applications in the macroscopic world and the unusual electronic and mechanical properties of nanotubes make them a good choice.
It becomes a poorer lubricant when it is heated in a vacuum.
An icosahedron is a shape formed by 20 equilateral triangles.
The original 12 vertices and 20 equilateral triangles have been replaced by 12 pentagons and 20 hexagons.
One day, nanotubes might be used to form wires for electronic devices.
Predicting the melting points and water solubilities of ionic compounds can be done with lattice energies.
We will look at how to calculate lattice energies.
The attractive force between a pair of oppositely charged ion increases with increased charge on the ion and decreased ionic sizes.
The lattice energies of most ionic compounds make it difficult for ion to leave the crystal and enter the gaseous state.
At normal temperatures, ionising does not happen.
We can disrupt the lattice with enough thermal energy.
The melting point of an ionic compound is determined by the lattice energy of the compound.
When an ionic crystal is dissolved, the energy required to break it up comes from the interaction of the ion and solvent.
The extent to which an ionic solid can be dissolved in a solvent depends on the lattice energy of the ionic solid.
The lower the lattice energy, the greater the quantity of an ionic solid that can be dissolved in a given quantity of solvent.