THE NATURE OF SOLIDS

by Mike, Marc & Alex

A Model for Solids

- Atoms, Ions or molecules are packed tightly together

- dense and not easy to compress

- solids tend to vibrate about

fixed points, they don't flow

State of Aggregation

- when heating a solid, particles vibrate more rapidly → kinetic energy increases

- when the solid reached its melting point it turns into a liquid

- the vibration is strong enough to overcome the attractions that hold them together

- melting and freezing point is at the same temperature

http://www.youtube.com/watch?v=kMR5KbNZ7b8&feature=related

Crystal Structure

- in a Crystal particles are arranged in an orderly, repeating, three-dimensional pattern called a crystal lattice

- Shape of a crystal reflects the arrangement of particles within a solid

Melting Points of Solids

- The melting Point of crystals is determined by the type of bonding between particles

- ionic solids have a high melting point → strong forces hold them together

- molecular solids have a low melting point

- Not all solids Melt (Wood, Cane Sugar)

Crystal Systems

A crystal has sides, or faces

- Sides and faces are always the same for a given substance

- There are 7 groups that crystals are classified into (Cubic, Tetragonal, Orthorhombic, Monoclinic, Triclinic, Hexagonal, Rhombohedral)

- Shape of crystal depends on arrangement of particles

- Smallest group within a crystal that retrains the geometric shape of crystal is known as a UNIT CELL

Allotropes Are two or more different molecular forms of the same

element in the same physical state

Only a few elements have allotropes

Non-Crystalline Solids

- Not all solids are crystalline; some are amorphous

- Amorphous solids lack an ordered internal structure

- Atoms are randomly arranged

- Glasses are one example for an amorphous Solid

- a glass is a transparent fusion of inorganic substances that have cooled to a rigid state without crystallizing.