Crystalline Solids

What is a crystalline solid?

A solid with long-range order and a repeating 3D pattern.

What is an amorphous solid?

A solid with no long-range order; only short-range organization.

What is a lattice point?

A position occupied by a particle.

What is a unit cell?

The smallest repeating unit of a crystal lattice.

Atoms per unit cell in Simple Cubic (SC)?

1 atom.

Coordination number of SC?

6.

Packing efficiency of SC?

52%.

Where do atoms touch in SC?

Along the edge.

Atoms per unit cell in BCC?

2 atoms.

Coordination number of BCC?

8.

Packing efficiency of BCC?

68%.

Where do atoms touch in BCC?

Along the body diagonal.

Atoms per unit cell in FCC?

4 atoms.

Coordination number of FCC?

12.

Packing efficiency of FCC?

74%.

Where do atoms touch in FCC?

Along the face diagonal.

Layering pattern of HCP?

ABABAB.

Coordination number of HCP?

12.

Packing efficiency of HCP?

74%.

Layering pattern of CCP?

ABCABC.

CCP is equivalent to what structure?

FCC.

Coordination number of CCP?

12.

Packing efficiency of CCP?

74%.

What are molecular solids made of?

Molecules at lattice points held by IMFs.

Properties of molecular solids?

Soft, low melting point, poor conductors.

Example of molecular solid?

Ice, CO2.

What are ionic solids made of?

Ions held by electrostatic attraction.

Properties of ionic solids?

Hard, brittle, high melting point, poor conductors as solids.

Example of ionic solid?

NaCl.

What are metallic solids made of?

Metal atoms with a sea of mobile electrons.

Properties of metallic solids?

Conduct electricity, malleable, variable melting points.

What are network covalent solids made of?

Atoms held by covalent bonds in a 3D network.

Properties of network covalent solids?

Very hard, extremely high melting point, poor conductors (except graphite).

Example of network covalent solid?

Diamond.

How is diamond structured?

Each C bonded to 4 C in 3D network.

Does diamond conduct electricity?

No.

How is graphite structured?

Each C bonded to 3 C; one delocalized electron.

Does graphite conduct electricity?

Yes.

Which is softer: diamond or graphite?

Graphite.

In NaCl structure, which ion forms FCC lattice?

Cl⁻.

Where does Na⁺ sit in NaCl?

Octahedral holes.

Coordination number in NaCl?

6:6.

Coordination number in CsCl?

8:8.

When does CsCl structure occur?

When ions are similar in size.

Structure of ZnS (zinc blende)?

S²⁻ forms CCP; Zn²⁺ occupies half tetrahedral holes.

Coordination number in ZnS?

4:4.

Radius ratio formula?

p = rsmall / rlarge.

If p < 0.4, coordination is?

Tetrahedral (CN=4).

If 0.4 < p < 0.7, coordination is?

Octahedral (CN=6).

If p > 0.7, coordination is?

Cubic (CN=8).

Smaller cation leads to what?

Smaller coordination number.

Bragg’s Law formula?

nλ = 2d sinθ.

What is Bragg’s Law used for?

Determining spacing between atomic planes.

What is n in Bragg’s law unless stated?

1.

What is coordination number?

Number of nearest neighbors.

CN of SC?

6.

CN of BCC?

8.

CN of FCC?

12.

CN of HCP?

12.

CN of NaCl?

6:6.

CN of CsCl?

8:8.

CN of ZnS?

4:4.

What is packing efficiency?

Percent of space filled by spheres.

Highest packing efficiency structures?

FCC and HCP (74%).

Lowest packing efficiency cubic structure?

Simple Cubic (52%).

Why do metals prefer close-packed structures?

Least wasted space.