Crystalline Solids CHM 115

Types of Crystalline solids, characteristics...

atomic

• particles:

• interparticle forces:

• physical properties:

• elements in what group?

atomic

• particles: atoms

• interparticle forces: dispersion

• physical properties: soft, low melting point, poor thermal and electrical conductors

• elements in what group? 18

molecular

• particles:

• interparticle forces:

• physical properties:

• elements that are nonpolar or polar?

molecular

• particles: molecules

• interparticle forces: dispersion, dipole-dipole, H Bonds

• physical properties: fairly soft, low to moderate melting point, poor thermal and electrical conductors

• elements that are: nonpolar

ionic

• particles:

• interparticle forces:

• physical properties:

ionic

• particles: pos. and neg. ions/cations and anions

• interparticle forces: ion-ion attraction

• physical properties: hard and brittle, high melting point, good thermal and electrical conductors when molten

metallic

• particles:

• interparticle forces:

• physical properties:

metallic

• particles: atoms

• interparticle forces: metallic bond

• physical properties: soft to hard, low to very high melting point, excellent thermal and electrical conductors, malleable and ductile.

network covalent

• particles:

• interparticle forces:

• physical properties:

network covalent

• particles: atoms

• interparticle forces: covalent bond

• physical properties: very hard, very high melting point, usually poor thermal and electrical conductors

What type of crystalline solid is carbon dioxide at very low temperatures? What particle interactions are present in the crystalline state?

CO2 at low temps is a molecular solid

IMFs: dipole-dipole interactions b/w molecules

Describe cubic packing

Cubic packing is an arrangement of atoms; cubic packing has diamond shaped holes

Describe hexagonal packing

Hexagonal packing has triangular holes

What type of packing is represented by this picture?

Cubic packing

What type of packing is represented by this picture?

Hexagonal packing

B/w cubic and hexagonal packing, which is denser

Hexagonal packing

What is the difference b/w a lattice and unit cell?

Lattice: a “repeating pattern” arrangement of atoms, ions, molecules

Unit cell: the smallest repeating structure of a lattice

The unit cell can be translated corner to corner to…

…generate the whole lattice.

This image represents?

Lattice

This image represents?

Unit cell

What are the 3 cubic systems?

• simple cubic

• body centered cubic (BCC)

• face centered cubic (FCC)

This image represents?

Simple cubic

What is the occupancy % of a simple cubic?

52%

This image represents?

Body centered cubic BCC

What is the occupancy % of a body centered cubic?

68%

This image represents?

Face centered cubic FCC

What is the occupancy % of a face centered cubic?

74%

Define occupancy

How much volume of the cell is occupied by spheres; packing efficiency

Occupancy is not…

density

What is the coordination number; what type of cubic?

6; simple cubic

What is the coordination number; what type of cubic?

8; body centered cubic

What is the coordination number; what type of cubic?

12; face centered cubic

Amount of atoms per unit cell of a simple cubic

1 atom/unit cell

Amount of atoms in this unit cell; type of unit cell?

1 atom/unit cell; simple cubic

Amount of atoms/unit cell of a BCC

2 atoms/cell

Amount of atoms in this unit cell; type of unit cell?

2 atoms/unit cell; body-centered cubic

Amount of atoms/unit cell of a FCC

4 atoms/cell; face-centered cubic

Amount of atoms in this unit cell; type of unit cell?

4 atoms/unit cell; face-centered cubic

C.

What is the formula for the radius of a simple cubic?

r = a/2

Image depicts what cubic type?

Simple cubic

C.

What is the formula for edge length of a BCC?

a = 4r/\sqrt{3}

This is image depicts what type of cubic?

Body-centered cubic

B. D = 4*r

What is the formula for edge length for a FCC?

A = sqrt8 * r

This image depicts what type of cubic?

FCC

At the 8 corners of a FCC, what fraction of an atom takes up each corner?

one eighth of an atom

at the 6 faces of a FCC, how much of an atom takes up each face?

one half of an atom

Which cubic types packs atom closest?

FCC

this information corresponds to which cubic type?

simple cubic

this information corresponds to which cubic type?

FCC

this information corresponds to which cubic type?

body-centered cubic

How does the edge length relate to the atomic radius of an FCC unit cell?

In an FCC unit cell, the edge length $a$ is related to the atomic radius $r$ by the equation a = 2*sqrt{2}*r due to the arrangement of atoms.

This image depicts what type of polymers?

Amorphous polymers

This image depicts what type of polymers?

semi-crystalline polymers; which exhibit both amorphous and crystalline regions.

In the crystal structure of NaCl;

• what is the cubic type?

• which ion follows the cubic type?

• which ion fits into the empty spaces?

• face centered cubic

• Cl anions follow the FCC structure

• Na cation fits into the empty spaces