Module H: The Solid State Nov 5

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Radius

Structure Coordination # Radius & Length

Simple Cubic 6 = /2

Body-centred Cubic (bcc) 8 4 = 3

Face-centred Cubic (fcc) 12 4 = 2

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Radius of a Metal atom Example 1:

At room temperature, iron crystallizes in a bcc structure. The edge of the cubic cell corresponding to Figure is found to be 287 pm. What is the radius of an iron atom?

Ans: 124 pm 3

Density Use data from Example 1, together with the molar mass of Fe

and the Avogadro constant, to calculate the density of iron in g/cm3.

1. Find mass of Unit cell.

2. Determine volume of unit cell.

3. Find density.

Density = mass/volume

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Phase Diagrams A phase is any sample of matter with definite composition and

uniform properties that is distinguishable from other phases with which it is in contact.

A process in which the physical form but not the chemical identity of a substance changes is called a phase change or a changes of state.

Triple point - the unique temperature and pressure at which the three states of matter, solid, liquid, and gas, coexist in equilibrium.

Critical point - At the critical point the liquid and vapour become indistinguishable

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Sketch a plausible phase diagram for hydrazine (N2H4) from the following data:

triple point = 2.0C and 3.4 mmHg,

the normal melting point = 2.0C,

the normal boiling point = 113.5C and

the critical point 380C and 145 atm.

The density of the liquid is less than that of the solid. Label significant data points on this diagram.

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