Solids and Phase Changes

Properties of Solids Molecules are tightly packed All IMF forces exert stronger effects in solids Forces hold particles in fixed positions Only vibrational movement around fixed points More order of particles due to stronger IMFs.

Types of Solids Crystalline—consist of crystals Crystal—particles are arranged in a orderly, geometric, repeating pattern. Amorphous—particles are arranged randomly.

Properties of Solids Definite shape and volume Crystalline solids—particles packed into crystal lattice Amorphous—when broken, maintain a definite shape but do not exhibit a distinct geometric shape. Glass—after being molded, shatters in irregular shapes

Properties of Solids Definite Melting Point for crystalline solids Melting—solid changes phase to a liquid by addition of energy as heat. Melting point—temperature at which solid becomes liquid KE of particles overcomes attractive forces Amorphous solids = no definite melting point Flow over range of temps Particles are arranged randomly like a liquid.

Properties of Solids High incompressibility High density Low rate of diffusion—millions of times slower than liquids or gases.

Crystalline Solids Crystal structures—used to show arrangements of particles in a crystal lattice. Unit cell—shows smallest unit of the repeating pattern of entire crystal

Crystalline Solids 4 types Ionic Contains positive and negative ions in a repeating pattern. Hard, brittle, high MP, good insulators Ex. MgCl2

Crystalline Solids Covalent network Each atom is covalently bound to the neighboring atom Hard, brittle, nonconductors or semiconductors Ex. SiO2, Graphite, Diamond,

Crystalline Solids Metallic Metals held together by sea of electrons Covalent molecular Individual molecules held together by IMFs Low MP, soft, good insulators

Phase Changes

Changes of State Phase change—any change from one state of matter to another. Requires energy transfer to occur Energy flows from higher energy particles to lower energy particles. Intermolecular forces (IMF’s) are also affected.

Processes that take energy Melting—changing from a solid to a liquid state Energy change? IMF’s? Sublimation—change of state from a solid directly to a gas. Vaporization—change of state from a liquid to a gas.

Phases releasing energy Condensation—gas changes to liquid state Energy change? IMF’s? Deposition—gas goes directly to a solid Same process as condensation, except on much cooler surfaces Freezing—liquid to solid

Equilibrium Condition in which two opposing changes occur at equal rates in a closed system.

Phase Diagrams Phase diagram—graph in which pressure versus temperature is used to show the conditions of phase changes for a specific substance. Triple Point—point at which all three states of matter coexist. Critical point—point of critical temp and critical pressure. Critical temp—temperature above which the substance cannot exist as a liquid Critical pressure—lowest pressure that substance can exist as a liquid.