Particles of
solids are not as free moving as particles of liquid. The particles of solids
tend to vibrate around a fixed point. When the particles are heated, they
vibrate more rapidly. Once the temperature reaches a certain point, the heat
creates more vigorous vibrating and the particles break free. This temperature
in which the particles “break free” is called melting point. Another way to say
it is as follows: melting point is the temperature at which a solid turns into
a liquid. To freeze a liquid is to turn it into a solid. Lastly, some
substances do not have a melting point; instead, they decompose.
A crystal is a substance in which the
atoms, ions, or molecules are arranged in an orderly, repeating,
three-dimensional pattern called a crystal lattice. Most solids are
crystalline. Because of the arrangement of the particles in a crystal, they
will have a uniform shape according to the crystal lattice. Crystals are
categorized into seven groups based on the intersection of the crystal sides
(also known as the angles) and the number of faces.
The smallest group of particles within
a crystal that retains the geometric shape of the crystal is known as a unit
cell. A crystal lattice is a repeating array of any one of fourteen kinds of
unit cells. Each crystal system has from one to four types of unit cells that
can be associated with the crystal system.
Allotropes are two or more different
molecular forms of the same element in the same physical state. An example of
an element that has this is carbon. Diamonds, graphite, and
buckminsterfullerene are all made up of carbon. These are all very different,
but they are all comprised of carbon.
Solids that are not in crystalline
form are called amorphous solids. They lack order and structure like the
crystalline solids. An example of amorphous solids is glass, rubber, plastic,
and asphalt. When amorphous solids break, they break rigidly, unevenly, and
jaggedly because they have no definite atomic structure.
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