Gold is a noble metal, which means that is
not very reactive. Some special chemistries,
however, do react with gold. For example, there is
an acid solution called "aqua regia." The name
means "king's water" in Latin because it can
dissolve the gold, which is a precious metal
associated with royalty. Aqua regia is made of a
boiling solution of nitric and hydrochloric acid.
These acids combined react with gold and make
"tetrachloroauric acid," which is a molecule
containing gold and chlorine.
Some examples of physical reactions with
gold include sputtering of gold and electroplating
of gold. Sputtering means that the gold is
vaporized and redeposited from the vapor onto a
surface. Think of it as kind of like spray
painting gold atoms onto a surface.
In electroplating, the gold atoms are dissolved
into a water-based solution and are deposited onto
the desired surface by using an electricity source
like a battery to attract the gold atoms to that
Gold is quite stable, so as a solid chunk it
doesn't react with much. This is why it has
been used in currency and jewelry, because it
doesn't corrode or oxidize over time. Gold is
stable to even strong acids, but a special
combination of nitric acid and hydrochloric acid
can dissolve it. This combination is known as
"aqua regia", which is latin for "royal
water," because of it's special ability to
dissolve gold. Gold is also able to be attacked by
a couple other things, including mercury and
sulfur-containing compounds. Mercury will dissolve
gold, and sulfur compounds will bind to gold.
As far as physical reactions, you can heat gold
up to make it melt, and it is prized for its
softness even as a solid. Because it's so
soft, it can easily be made into wires that are
thinner than human hair, or into ultra-thin sheets
that are only a few atoms thick. Pure gold is very
soft, but also chemically resistant, which makes
it great for dental caps, and which is why gold
caps have traditionally been the best material for
dental work up until recently. Now,
specially-designed advanced ceramics are becoming
more popular, and are much cheaper.
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