Cesium chloride (cubic 8:8)[edit]

At high temperature and pressure, RbCl adopts the CsCl structure (NaCl and KCl undergo the same structural change at high pressures). Here, the chloride ions form a simple cubicarrangement with chloride anions occupying the vertices of a cube surrounding a central Rb+. This is RbCl's densest packing motif.[2] Because a cube has eight vertices, both ions' coordination numbers equal eight. This is RbCl's highest possible coordination number. Therefore, according to the radius ratio rule, cations in this polymorph will reach their largest apparent radius because the anion-cation distances are greatest.[4]
This page may help with sample problems to find the formula mass of a unit cell:

Hydrogen Bonds:

Hydrogen bonds can only form when hydrogen is bonded to N, O, or F.

To find the radius:

Use this site:

Hypothetical Element:

On the problem that starts with "A hypothetical element is found to have a density of..."
When it says face-centered cubic use 4 atoms as the number of atoms.
When it says "simple cubic" use 1 atom.
Also, use 6.023 x 1023 atoms and find the answer in amu.

Degrees Freedom

Look at this site:

Find the density of a closely paced Structure:

The length of a cubic close-packed unit cell is length = 81/2 r, where r is the atom’s radius.

Interaction between two species is proportional to 1/r2

1/r2 is proportional to ion-dipole interactions. A reaction of some sort.

Potential energy problem:

or any problem that wants an answer in "j (joules)" use the "R (gas constant)" value that have joules in it.


Water Vapor Problems:

Sometimes you have to use this formula above to solve for delta H then turn around and use it again to get a temperature.
Critical pressure is the point where you can no longer get a vapor.
external image 700px-Phase_diagram_of_water.svg.png