CHEM 281 LAB: SOLID STATE STRUCTURE OF METALS AND IONIC COMPOUNDS

Objective: The purpose of this experiment is to extend our understanding and familiarity of the three dimensional structures of solids. We will use models and the Institute for Chemical Education (ICE) Solid-State Model Kits and CaRline Crytaloography software which are designed for creating a variety of common and important solid state structures.

Aamorphous solids: Solids that do not possess any long-range order, so they do not typically form well-defined faces nor do them fracture evenly. Glass is an example of an amorphous solid. Amorphous solids have very interesting properties in their own right that differ from those of crystalline materials. We will not consider their structures in this laboratory exercise.

Classification of crystalline materials

The forces which stabilize the crystal may be ionic (electrostatic) forces, covalent bonds, metallic bonds, London dispersion forces, hydrogen bonds, or a combination of these. The properties of the crystal will change depending upon what types of bonding is involved in holding the atoms, molecules or ions in the lattice. The fundamental types of crystalline solid are based upon the types of forces that hold them together are:

Metallic Solids	Metal cations held together by a sea of electrons
Ionic Solids	Cations and anions held together by predominantly electrostatic attractions
Network Solids	Atoms bonded together covalently throughout the solid (also known as covalent crystal or covalent network).
Molecular Solids	Collections of individual molecules; each lattice point in the crystal is a molecule

Often crystals held together by more than one type of force and thus may have intermediate properties.

Structure of Metals

The structures of pure metals are crystalline (crystal lattice) with regular arrangement of metal atoms that are identical perfect spheres. For cubic system, they form four basic structures: simple cubic (SC), body-centered cubic (BCC), hexagonal closest-packed (HCP), and cubic closest-packed (CCP).

Crystal lattice

The structures of pure metals are crystalline (crystal lattice) with regular arrangement of metal atoms that are identical perfect spheres.

Coordination number (CN): The number of nearest neighboring metal atoms (four, six, eight to twelve) which each atom is surrounded in the crystal lattice.

Crystal Packing

Unit cell:

Wallpaper has regular repeating design that extends from one edge to the other. Crystals have a similar repeating unit called unit cell that extends in 3-D from one edge of the solid to the other. Unit cell has, three edges, a, b, c and there angles, .

Filling efficiency: Is the percent ratio of volume filled by the metals to the total unit cell volume.

Cubic crystal system (a = b= c and there angles, 90.

For the cubic crystals, there are four basic unit cells.

Cubic Crystal Structures

Stacking Pattern	Structure (Unit cell)	Coordination Number	Filling efficiency
Open-packed A on top of A B in spaces of A layers	AAAAAAAA. . .	simple cubic (SC)	6	52%
ABABABAB. . .	body-centered cubic (BCC)	8	68%
Close-packed Between the spaces of layer below	ABABABAB. . .	hexagonal closest-packed (HCP)	12	74%
ABCABCABC. .	cubic closest-packed (CCP-FCC)	12	74%

Part of the Atom in the Unit Cell

The part of the atom in the unit cell is counted according to the following locations

corner = 1/8	edge = 1/4	face = 1/2	body = 1

Number of Atoms in the Cubic Unit Cell

SC = 1 (8 corners)	FCC = 4 ( 8 corners, 6 faces)
BCC = 2 (8 corners, 1 body)	Other unit cells?

Interstitial Sites and Holes: The remaining unoccupied space in any sphere packing scheme of unit cell is found as void space. This void space occurs between the spheres and gives rise to so-called holes.

Holes: The easiest way to determine the type of hole is by looking at how the atoms surround the ion in the hole.

Hexagonal (HCP) and cubic close packing (CCP-FCC):

Octahedral hole: Space in an octahedral hole is surrounded by six other metals oriented octahedral.

Octahedral hole: Space in an tetrahedral hole is surrounded by four other metals oriented tetrahedrally.

Bravais Lattice: A Bravais Lattice is a three dimensional lattice. A Bravis Lattice tiles space without any gaps or holes. There are 14 ways in which seven crystal systems this can be accomplished. Basic types of Bravais unit cells P (primitive),I (body centered, F(face centered), C (centered on c axis) and R/P (rombohedral/primitive)

Seven Crystal Systems

Crystal Systems	Unit cell Constraints	Fourteen Bravis Lattices
Cubic	a = b c, 90	P,I,F (3)
Tetragonal	a =b c,  90	P, I (2)
Orthorhombic	a b c,  90	P, C, I, F (4)
Trigonal	a = b c, 90	R/P (1)
Monoclinic	a b c, 90	P, C (2)
Hexagonal	a = b c, 90, 120	P (1)
Triclinic	a b c,  90	P (1)
Crystal structure
Cesium chloride structure:
Rock Salt Structure:
Fluorite Structure:
Sphalrite Structure:
Wurtzite:
Rutile:
Pervoskite structure:

Ionic crystal structures:

LAB Activity:

Using the materials given to you build following cubic staking patterns and identify the units cells they created. Draw a picture of your model.

Open-packed A on top of AAAAAAAA.

Open-packed A on top of B in spaces of B layers :ABABABABAB.

Close-packed A between the spaces of B layer: ABABABABAB.

Close-packed A between the spaces of layer B and B on C but A and C are displaced:

Using software create following cubic unit cells and compare to the model provided draw a picture to show interstitial sites and identify octahedral, cubic and tetrahedral holes.

Simple cube (SC):

Body-centered cubic (BCC):

Cubic closest-packed (CCP-FCC):

Hexagonal closest-packed (HCP):

Using software create following unit cells and compare them to models and label the origin, axes and angles

a) Tetragonal I

b) Orthorhombic P

c) Trigonal R/P

d) Monoclinic C

e) Hexagonal P

f) Triclinic P

g) Cubic F

Identify the fourteen Bravais Lattice (unit cells) given and classify them into seven crystal systems

Crystal Systems	Unit cell Constraints	Fourteen Bravis Lattices
a =b c,  90	P, I (2)
a = b c, 90	P,I,F (3)
a = b c, 90, 120	P (1)
a = b c, 90	R/P (1)
a b c,  90	P, C, I, F (4)
a b c, 90	P, C (2)
a b c,  90	P (1)

5. Identify the Miller indices of the planes in crystalline lattices of rock salt structure:

Using software create unit cells following crystals systems identify the a) cell type (SC, BCC, FCC etc.) b) and the coordination number and c) the type of hole ions are occupying

Using software create NaCl crystal structure using following data. Unit cell dimentions: a =b c= 5.5 Å,  90

Crystal structure	a) Cell	b)M(CN)	c) M Hole	X(CN)	c) X Hole	Formula, MX
1	Cesium chloride structure:	Cs+=	Cl-=	CsCl
2	Rock Salt Structure:	Na+=	Cl- =	NaCl
3	Fluorite Structure:	Ca2+=	F- =	CaF2
4	Antifluorite	K+ =	O-2 =	K2O
5	Sphalrite Structure:	Zn2+=	S-2 =	ZnS
6	Wurtzite:	Zn2+=	S-2 =	ZnS
7	Rutile:	Ti4+=	O-2 =	TiO2
8	Pervoskite structure:	Ca2+= Ti4+=	= =	O-2 =	CaTiO3