12 -- Part 6: Intermolecular Forces: Liquids and Solids
The cation occupies a hole that maximizes the attractions between the cation and anion.
The cations can be accommodated into smaller holes than the actual size of the ion.
The anion and cation are in contact, maximizing attractions, and this pushes the anions of the closest packed array slightly apart.
If a cation is to occupy a hole in a simple lattice, the radius will be governed by the inequality of 0.414 6 1rcation>Ranion2 6 0.732 where the upper limit of the inequality corresponds to the hole in a simple lattice.
The criteria given here can be used to rationalize the structures of ionic particles.
We must be aware of the limitations of the model.
We assumed that there were no interactions other than the coulombic attractions.
If this is not the case, the criteria will fail.
The criteria will be very useful.
These structures can be looked at for their consistency with the formula of the compound and the hole the cation occupies.
We expect Na+ ion to occupy the holes of the closest packed KEEP IN MIND array.
To establish the formula of the compound, we must apportion the 27 ion in array of spheres among the unit cell and its neighboring unit cells.
How this apportioning is done is shown in Figure 12-42.
Only the centers of the ion are shown for clarity.
The charged ion are in contact.
We can think of this structure as an fcc lattice of cations, with Na+ ion filling the holes.
The Cs+ ion is in the center of the cube.
There is an alternative unit cell with Cs+ at the corners.
The total number of Na+ ion in a unit cell is 12.
The formula is 1 : 1 and the ratio is 4 : 4.
The number of nearest neighbor ion of opposite charge to any given ion in the crystal is used to establish the coordination number.
The difference in the structure of the two compounds can be accounted for.
99 and 181 pm are the ionic radii of Na+.
Understanding geometric relationships in the unit cell is the key to solving this problem again.
The edge length is equal to the diameter of Na+ and the radius of another Cl-.
We need to remember the atomic arrangement of the unit cell to determine the geometric relationships.
The ionic radius of Cs+ is 167 pm.
The zinc blende structure is an fcc lattice of anions with cations.
Each cell has four cations and four anions.
The zinc blende structure has four cations and eight anions per cell.
The spacefilling model shows Ti4+ and O2 unit cells.
The rutile structure boundaries of this unit cell are penetrated by adjacent unit cells.
There are two Ti4+ ion and four O2 ion per cell when the fractions of spheres are added.
We think that the Cs+ ion will occupy a hole in the lattice.
There are ionized compounds of the type M2+X2 that can form crystals of the NaCl type.
If the cation is small enough, it can occupy the tetrahedral holes.
Half of the holes are occupied to correspond to the four S2 forming the face-centered cubic array, which is why the radius ratio for ZnS is 0.35.
CaF2 has more calcium ion than fluoride ion.
The easiest way to see this is by looking in the middle of the face.
There are four neighbors within the unit cell.
The nearest neighbors are F ion.
A coordination number of eight is given for the Ca2+.
A coordination number of four is given by F ion as nearest neighbors.
Two of the O2 ion are in the interior of the cell, two are in the top face, and one is in the bottom face of the cell.
The center of the cell and the corners are where Ti4+ ion are located.
Buckminsterfullerene C is in a face-centered array.
The concept of lattice energy is most useful when it is stated in quantitative terms.
It is not easy to calculate a lattice energy directly.
The problem is that oppositely charged ion attract one another and repel one another, and these interactions must be considered at the same time.
The crux of the method is to design a sequence of steps in whichenthalpy changes are known for all the steps but one step in which a crystal lattice is formed.
There is a method for finding the lattice energy of NaCl.
NaCl(s) is formed by combining Na+1g2 and Cl-1g2
In the following setup, the lattice energy of NaCl is the only unknown.
C/ rH3 is the first ioniz.
A five-step sequence for the formation of NaCl from its elements in their standard states is shown here.
The same one-step reaction is shown in color.
The kJ mol-1 + C/rH5 convention is used to define lattice energy.
Predicting the possibility of synthesizing ionic compounds is one way to use the concept of lattice energy.
We predict the likelihood of -1lattice energy2.
The enthalpy of dissociation of Cl2(g) is +243 kJ mol-1 and the Enthalpy is + 146 kJ mol-1.
We draw an enthalpy diagram for the formation of an ionic solid.
The diagram shows that the lattice energy (C/rH5) is known, and the unknown is C/rHoverall.
These types of problems are not new to the law.
The enthalpy diagram is used to keep the equations straight.
The enthalpy is 78.2 kJ mol-1, which is 442.8 kJ mol-1.
The lattice energy of CsCl(s) can be calculated using these values and other data from the text.
It has a slightly negative enthalpy of formation, so it can be obtained as a stable compound.
You might think that if there is a limited amount of Cl21g2, then there should be a form of MgCl.
This is not the case.
The lattice energy is much greater for MgCl21s2 than it is for Mg+.
The more stable magnesium and chlorine react to each other.
The answer is no.
There is an acronym for liquid crystal display.
The material in this chapter makes the use of the word liquid confusing.
For a discussion of the properties and uses of materials that we call liquid crystals, go to the Focus On feature for Chapter 12.
There are some properties of polar substances.
In living systems the reverse process is called force.
Intermolecular forces are related to 12-26.
A graphical plot of conditions under which as drop shape, meniscus formation, and capillary action solid, liquids, and gases exist, as single phases depend on surface tension is a familiar phenomena.
According to the nature of bonding, the dependence is classified.
Liquids and Solids bonds hold the atoms in place.
Solids composed of 39.
In some cases where spheres are not packed, the molecule is held in place through the different intermol closely as in the hcp and fcc structures.
The dimensions and delocalized electrons can be used to calculate atomic free movement throughout the solid.
A mole of an ionic solid can be formed by an array of ionic crystals.
The packing of spheres can be described by some crystal structures.
When a container filled with an equilibrium mixture of N2H4(g) and N2H4(l) is at 25.0 degC, use data from the table of physical properties of hydrazine to calculate the partial pressure of N2H4(g).
The hydrazine will be present as a solid in equilibrium with its vapor at a temperature of 2.0.
We are looking for the pressure of N2H4 at the melting point of ice.
The hydrazine is in three phases at its freezing point.
The vapor pressure of hydrazine needs to be determined.
The Clausius-Clapeyron equation can be used to calculate the vapor pressure.
Identifying the data needed to apply the Clausius-Clapeyron equation three times is our main task.
298.2 K was obtained.
The same data as J mol-1 K-1 is used in the first calculation for T. The equation for P P2 is 0.235.
The triple point data for hydrazine is now available.
The triple point pressure is 3.38 Torr.
The unknown pressure is P1.
The calculated triple point pressure (3.38 Torr) is smaller than the vapor pressure at 25 degC (14.4 Torr).
The trend is expected for the three values.
In the three situations in which equation (12.2) is used, the first one is the most subject to error because the difference between T2 and T1 is 89 degC, while in the other two it is 23 degC and 2 degC, respectively.
Both C/subH and C/vapH are temperature dependent.
The normal boiling point of isooctane is 99.2 degC, and its C/vapH is 35.76 kJ mol-1.
The Born-Haber cycle can be used to indirectly obtain the second electron affinity.
The lattice energy is -3925 kJ mol-1.
The double-stranded helix is formed by hydrogen bonds between the nucleic acid bases.
Water will form clusters.
If you want to draw a water cluster, you need to maximize the number of hydrogen bonds for each water molecule.
When a sample of liq temperature remains roughly con uid acetonitrile, CH3CN, it absorbs 1.00 kJ of heat at its stant.
The liquid evaporated from the normal boiling point.
How much water would you expect to evaporate?
A 50.0 g piece of iron is dropped into 20.0 g heats of iron and water in an open, thermally insulated environment.
The boiling point of water is 94.
The volume of He(g) is passed through 0.486 g.
The density of acetone vapor in equilibrium with liq is assumed to be 0.876 g L-1.
The total gas volume and tempera are expressed in ture and remain constant.
A 7.53 L sample of N21g2 is required for cooking.
The water is boiled in a bubble through CCl41l2.
If the steam gas becomes saturated with CCl4(g), what is the vol condenses on the outside walls of an inner container if the total cooking occurs?
What is it?
A popular demonstration in chemistry labs is per 6.0 atm.