The Nature of Solids & Changes of State Miss K. Marshall
Jan 01, 2016
The Nature of Solids & Changes of StateMiss 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