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 ionic Compounds

The structures of ionic solids are crystalline (crystal lattice) with regular arrangement of cations and anions that are perfect spheres with different ionic radii. Cations fit into the holes in the anionic lattice since anions are noramllylager than the cations. In cases where cations are bigger than anions lattice is considered to be made up of cationic host lattice with smaller anions filling the holes. For various host lattice systems, based on simple cubic (SC), hexagonal closest-packed (HCP), and cubic closest-packed (CCP) there are about 7 basic ionic lattice types:

Cubic open packing (bcp):

CsCl Structure: MX type

A crystal lattice of CsCl (MX) based on AB open packing similar to metals but

intertwined A+B+ layers of cations (M+) and A-B- layers of anions (X-) makinga a body centred cubic (bcc).

Cubic Close packing (ccp or fcc):

Rock Salt Structure: MX type

A crystal lattice of NaCl (MX) based on ABC close packing similar to metals but

intertwined A+B+C+ layers is cations (M+) and A-B-C- layer of anions (X-) making cubic

close packed (ccp) or face centered cube (fcc).

Fluorite Structure:MX2 type

A crystal lattice of CaF2 (MX2) based on ABC close packing of Ca2+ ions in a fcc unit

cell and 8 F- ions in the tetrahedral holes in the body of the fcc.

Sphalrite Structure:mx MX type

A crystal lattice of ZnS (MX) based on ABC close packing of S2- ions in a fcc unit cell

and 4 Zn2+ ions in the tetrahedral holes in the body of the fcc.

Rutile: A crystal lattice of TiO2 (MX) based on ABA close packing of O2- ions in a hcp unit cell and Ti4+ ions in the octahedral holes in the body of the hcp.

Pervoskite:

Hexagonal Close Packing (hcp):

Wurtzite: A crystal lattice of ZnS (MX) based on ABA close packing of S2- ions in a

hcp unit cell and Zn2+ ions in the tetrahedral holes in the body of the hcp.

A crystal lattice of CaTiO3 (MM’X3) based on AA open packing of Ca2+ ions in a

simple cube (sc) unit cell with and 6 O2- ions in the six faces of cube and one Ti4+ in the

cubic home of the simple cube.

Crystal lattice

The structures of ionic compounds are crystalline (crystal lattice) with regular arrangement of spherical ions in one of the above ionic lattice types.

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, .

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

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

Ionic crystals are found among all 7 crystal systems with specific unit cells.

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)

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 host ion packing scheme of host unit cell is found as void space. This void space occurs between the spheres and gives rise to so-called holes. These holes could be filled with a smaller ion to give various ionic lattices.

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 structure
Cesium chloride structure:
Rock Salt Structure:
Fluorite Structure:
Sphalrite Structure:
Wurtzite:
Rutile:
Pervoskite structure:

Ionic crystal structures:

CHEM 281 LAB #5 Activity (Lattices of ionic compounds):

Using the model kit build the following lattice types. Give the page number and card number and raw the structures:

Cesium chloride structure: (CsCl)

Rock Salt Structure: (NaCl)

Fluorite Structure: (CaF2)

Sphalrite Structure: (ZnS)

Wurtzite: (ZnS)

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

Give the number of ions per unit cell and the formula of the pervoskite structure of superconducting material (1-2-3:Y-Ba-Cu) given below:

Complete the table:

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