Chemistry Reference
In-Depth Information
Minerals, mineraloids, and metals are advantageous for specific appli-
cations because of one or more of their physical properties. The
softness
of
soapstone, for example, makes this mineral useful for shaping and carving
objects. The very opposite, the extremely high
hardness
of diamond and
emerald, makes them resistant to wear and scratching and, therefore, valued
as gemstones. It is also because of its extreme hardness that powdered
diamond is the best abrasive material for rubbing, grinding, and polishing
solids. Other extremely useful physical properties of materials are color and
the refractive index (see Textbox 22). The
color
of many materials, such as the
characteristic red of
minium
(a lead-containing mineral) and the green of
malachite
(a copper-containing mineral) makes them useful as pigment, while
the high
refractive index
of diamond and emerald makes these two rare min-
erals glitter and sparkle and, therefore, desirable and highly valued as gem-
stones often set into jewelry.
TEXTBOX
6
ATOMS AND MOLECULES; CHEMICAL NOMENCLATURE AND
FORMULAS
Elements and Atoms
The
chemical elements
, the building blocks of all matter, are made up of
identical atoms (see Textbox 2). Very few elements, however, occur on
earth singly, uncombined with others. Most are chemically combined with
other atoms, either identical or different. Examples of elements that may
occur singly are the metals copper and gold and the nonmetal sulfur, which
are often found in their
native
form in the crust of the earth. The gaseous
elements
oxygen
and
nitrogen
, the main components of the earth's atmos-
phere, occur as molecules composed of two identical, combined atoms;
each atom in a molecule of oxygen or nitrogen is combined to another
atom of the same element.
Most elements, however, are naturally combined with one or more
other elements, forming compounds. Water and calcium carbonate (also
known as
calcite
,
limestone
, or
marble
) are examples of common com-
pounds formed by the combination of two or more elements; in water,
one atom of oxygen is combined with two of hydrogen; and in calcium
carbonate, one atom of carbon is combined with three of oxygen and one
of calcium.
