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The nature 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..
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A model for solids • The general properties of solids reflect the orderly arrangement of their particles and the fixed locations of their particles.. • In most solids, the atoms, ions , or molecules are packed tightly together. These solids are dense and not easy to compress. Because, the particles in solids tend to vibrate around fixed points, solids don’t flow. • When you heat a solid, its particles vibrate more rapidly as their kinetic energy increases. The organization of particles within the solids breaks down, and eventually the solid melt
The melting point • Is the temperature at which a solid changes into a liquid. • At this temperature, the disruptive vibrations of the particles are strong enough to overcome the attractions that hold them in fixed positions, • The melting and the freezing points of a substance are at the same temperature.
Crystal structure and unit cells • The shape of the crystal reflects the arrangements of the particles within the solid. • The smallest group of particles within a crystal that retains the geometric shape of a crystal is called a unit cell. • Allotropes are two or more different molecular forms of the same element in the same physical state, although allotropes are composed of atoms of the same element, they have different properties because their structures are different.
Non-crystalline solids • An amorphous solid lacks an ordered internal structure like plastic and rubber. These atoms are randomly arranged • When a crystalline solid is shattered , the fragments tend to have the same surface angles as the original solids. By contrast, when an amorphous solid is shattered, the fragments have irregular angles and jagged edges.
Changes of state • Sublimation is the change of a substance from a solid to a vapor without passing through the liquid state . • Sublimation occurs in solids with vapor pressure that exceed atmospheric pressure at or near room temperature. • Sublimation has many useful application. • 1. if freshly brewed coffee is frozen and the water vapor is removed with a vacuum pump, the result is a freeze-dried coffee • 2. solid carbon dioxide (dry ice) used as a coolant for goods as ice cream. because it sublimes, it doesn’t produce liquid as ordinary ice • 3. sublimation also is used to separate mixtures and to purify compounds.
Phase diagram • The relationship between the solid, liquid , and vapor state of a substance in a sealed container can be represented by a single graph. • A phase diagram gives the condition s of temperature and pressure at which a substance exists as a solid, liquid, and vapor. • 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.
The phase diagram of water • - in each of the colored area of the diagram, the water is in a single phase. • - The curving line that separates water vapor’s phase from the liquid phase are the equilibrium conditions of the liquid and the vapor. • The triple point describes the only set of conditions at which all three phases can exist in equilibrium with one another.
