CRYSTALLINE AND NON-

CRYSTALLINE MATERIALS

WHAT IS CRYSTALLINE SOLID

What is crystalline solid ?

Four types of crystalline solid :

>Ionic solids

Structure: NaCl

Other example: MgO, CaF2, LiCl, CaCl2.

*it is usually made up of Alkali or Alkali Earth Metal elements reacted to Halogen group of elements

>Molecular solidsStructure: solid sucrose

Other examples: CH4, CO2, ice .

>Atomic solids

Structure:

>Metallic solidsThe atoms are held together by strong metallicbonding forces .

Examples: Fe, Cu, Ti, Na*It is usually made up of Alkali, or Alkaline

Earth metals.

NON-CRYSTALLINE MATERIALS

Exaples: Plastic, wax and glass.

CRYSTALLINE SOLID STRUCTUREUnit Cell – building block of entire crystall.

COMMON TYPES OF UNIT CELL IN ENGINEERING METALSBCC- body centered cubic

the cube edge length, a= 4R/√3Number of atoms per unit cell, n = 2V = a3

FCC- FACE CENTERED CUBIC

cube edge length, a= 2R√2Number of atoms per unit cell, n = 4V = a3

HEXAGONAL CLOSE-PACKED CRYSTAL STRUCTURE

Number of atoms per unit cell, n = 6

COMPUTATION:

ρ =

n-#of atomsA-atomic weight Vc- volume of the cellNA- Avogadro’s number

ATOMIC PACKING FACTOR

THE SEVEN CRYSTAL SYSTEMS

References:

http://www.sparknotes.com/testprep/books/sat2/chemistry/chapter5section2

N. W. Ashcroft and N. D. Mermin, Solid State Physics (Saunders College Publishing,Texas, 1985).