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

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.