The Nature of Solids By Allen Tang, Dan Jacobson, and Ted Dennis.

A Model for Solids Properties of solids reflect the arrangement of their particles Melting point-the temperature at which a solid changes into a liquid – Ionic compounds have high melting points – Molecular solids have relatively low melting points

Crystal Structure Crystal-the particles are arranged in an orderly, repeating, three-dimensional pattern called a crystal lattice Shape of a crystal reflect the arrangement of the particles

OBJECTIVE 17. What makes solids different from liquids and gases according to KMT? In solids, the particles are arranged in fixed locations.

OBJECTIVE Unit Cells 14 types Repeating array Crystal System Seven groups 18. Compare and contrast the terms crystal system and unit cell.

Crystal Systems A crystal has sides, or faces Crystals are classified into seven distinct crystal groups, or crystal systems The angles at which the faces of a crystal intersect are always the same for a given substance. – Thus, the crystal system of a sample of galena (a cubic system) will be identical in shape to the crystal system of another similarly sized sample.

Unit Cell A unit cell is the smallest group of particles within a crystal that retains the geometric shape of the crystal. A crystal lattice forms from a repeating array of any one of the fourteen kinds of unit cells. A unit cell is similar to a crystal system in that it defines the shape of said system by the bonding of its atoms, yet it is different in that a crystal system can consist of any amount of compounds while still retaining the structure of its original system, while a unit cell exists only as the smallest group of particles that create a crystal system

Allotropes Two or more different molecular forms of the same element in the same physical state. They have different properties because their structures are different, even though they are all made up of the same element. Example: Diamond vs. Graphite (carbon)

Objective 19. Explain how three allotropes of carbon produce different functions. Diamond, graphite and fullerenes are all composed of carbon, but have different molecular structures. Because of this the physical properties are different. Diamond has a high density and is very hard. Graphite has a low density and is soft. Fullerenes are strong and rigid.

Non-Crystalline Solid Amorphous solid- lacks an ordered internal structure; the atoms are randomly arranged (Ex: rubber, plastic and asphalt). Glass-The transparent fusion product of inorganic substances that have cooled to a rigid state without crystallizing