The Nature of Solids

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The Nature of Solids Changes of State

• Miss K. Marshall

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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.

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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
• Particles are packed tightly together
• dense
• Not easily compressed
• Particles vibrate in fixed locations
• Do not flow

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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

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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.

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Crystal Structure and Unit Cells
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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

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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

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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

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• 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

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Changes of State

• Connecting to Your World
• Water
• Weather patterns

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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

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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

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