The Nature of Solids & Changes of State Miss K. Marshall

Connecting to your world  In 1985, a new form of carbon discovered  buckyball  Carbon buckminsterfullerene  What will we learn in this section?  How the arrangement of particles in solids determines the general properties of solids.

A Model for Solids The general properties of solids reflect the orderly arrangement of their particles and the fixed locations of their particles  Particles are packed tightly together  dense  Not easily compressed  Particles vibrate in fixed locations  Do not flow

A Model for Solids (continued)  As temperature what happens to kinetic energy?  What is the effect on the particles of a solid?  Organization eventually breaks down, solid will melt  Melting point (mp)  the temperature at which a solid changes into a liquid  Overcome intermolecular forces

Crystal Structure and Unit Cells  Most solid substances are crystalline  crystal  a substance in which the particles are arranged in an orderly, repeating, three-dimensional pattern called a crystal lattice  ****The shape of a crystal reflects the arrangement of the particles within the solid.

Crystal Structure and Unit Cells

Crystal Structure Ionic solids have high melting points because strong forces keep them together Molecular solids have low melting points because the forces that keep them together are weak Not all solids melt  some decompose Examples? Cane sugar, wood

Crystal Systems  Crystal has sides (faces)  Angles at which the faces of a crystal intersect are always the same for a given substance and are characteristic of that substance  Unit cell  The smallest group of particles within a crystal that retains the geometric shape of the crystal

Allotropes Some solid substances can exist in more than one form ◦Known as allotropes: two or more different molecular forms of the same element in the same physical state Example: carbon ◦Graphite (pencils) ◦Diamond

 Not all solids are in crystalline form; some are amorphous  Lacks an ordered internal structure  Example: rubber, plastic, asphalt, glass  glass  A transparent fusion product of inorganic substances that have cooled to a rigid state without crystallizing  Do not melt at a definite temperature – gradually softens

Changes of State  Connecting to Your World  Water  Weather patterns

Sublimation  Sublimation  The change of a substance from a solid to a vapor without passing through the liquid state  ****sublimation occurs in solids with vapor pressures that exceed atmospheric pressure at or near room temperature.  Solid carbon dioxide (dry ice)  Solid air fresheners

Phase Diagrams  Phase Diagram  A single graph that represents the relationships among the solid, liquid, and vapor states (or phases) of a substance in a sealed container  Pressure (y-axis); temperature (x-axis)  ****The conditions of pressure and temperature at which two phases exist in equilibrium are indicated on a phase diagram by a line separating the phases

Triple point – describes the only set of conditions at which all three phases can exist in equilibrium with one another