Solids Motion Arrangement Vibrate about center of mass

Solids

Motion & Arrangement • Vibrate about center of mass. – Cannot “translate” or move from place to place. – Cannot slide past each other or flow. • Packed closely together. – IMF work better when particles are close together. – Tend to be orderly. – High density • 100’s of times denser than gases • Slightly denser than liquids – Virtually incompressible

States of Matter source 1. 2. 3. 4. How are the particles packed in each phase? How do the particles move in each phase? Why do liquids and gases flow? Why are gases so easy to compress?

Types of Solids • Crystalline solids: made of crystals – Particles arranged in orderly, repetitive, 3 -D pattern – Ionic – Metallic – Network Covalent – Molecular Covalent • Amorphous solids: particles arranged randomly – Glass & plastics

Properties of Solids • Definite shape, definite volume • Definite melting point – crystalline solids – Melting: physical change of a solid to a liquid by the addition of heat energy – Melting point: temperature at which a solid becomes a liquid. – Crystalline solids melt at a distinct temperature. That’s why it’s called a point! – Amorphous solids melt over a temperature range.

Supercooled liquids • Substances that retain certain liquid properties even at temperatures at which they appear to be solids.

Crystal Structure • Total 3 -D arrangement of particles in a crystal. – Can be one perfect crystal, a “single crystal” – Can be lots of little crystals all fused together • Structure has two parts – Lattice: geometric arrangement of points in space at which atoms, molecules, or ions of a crystal occur. – Unit Cell: smallest portion of lattice that shows 3 D pattern of the entire lattice.

Covalent Molecular Crystals • Covalently bonded molecules held together by IMF – Molecular: molecule at each lattice point. • Polar molecules held together by dipole-dipole forces – Sugar • Nonpolar molecules held together by London dispersion forces – CO 2, S 8, P 4 – Weakest IMF so lowest melting points

Covalently bonded network solids • Each atom is covalently bonded to its nearest neighbors • Only four you need to know – Diamond (C in 3 -D pattern) – Graphite (C in 2 -D pattern) – Si. O 2 (quartz crystals) – Silicon carbide • Like giant molecules. Hard and brittle, high melting points, insoluble, usually nonconductors.

Other crystalline solids • Ionic solids: composed of metal & nonmetal ions • Metals: composed of positive metal ions in a sea of mobile electrons

Amorphous solids • Maintain a definite shape • But don’t have distinct geometric shapes like crystals • Can be molded into lots of irregular shapes.