|
Symbol
|
Au
|
|
Atomic number |
79 |
|
Atomic mass |
196.9655 g.mol -1 |
|
Electronegativity ccording
to Pauling |
2.4 |
|
Density |
19.3 g.cm-3 at 20°C |
|
Melting point |
1062 °C |
|
Boiling point |
2000 °C |
|
Vanderwaals radius |
0.144 nm |
|
Ionic radius |
0.137 nm (+1)
|
|
Isotopes |
7 |
|
Electronic shell |
[ Xe ] 4f14 5d10 6s1 |
|
Energy of first
ionisation |
888 kJ.mol -1
|
|
Energy of second
ionisation |
1974.6 kJ.mol -1
|
|
Standard potential |
+1,68 V ( Au+/ Au ) |
Gold
Gold is
metallic, with a yellow colour when in a mass, but when finely divided it may be
black, ruby, or purple. It is the most malleable and ductile metal; 1 ounce (28
g) of gold can be beaten out to 300 square feet. It is a soft metal and is
usually alloyed to give it more strength. It is a good conductor of heat and
electricity, and is unaffected by air and most reagents.
Gold
is usually alloyed in jewellery to give it more strength, and the term carat
describes the amount of gold present (24 carats is pure gold). It is estimated
that all the gold in the world, so far refined, could be placed in a single cube
60 ft. on a side.
The
most common gold compounds are auric chloride (AuCl3) and chlorauric
acid (HAuCl4). A mixture of one part nitric acid with three of
hydrochloric acid is called aqua regia (because it dissolved gold, the King of
Metals). It is unaffected by air and most reagents.
Applications
Gold is used as buillon and in jewellery, glass and electronics. Jewellery
consumes around 75% of all gold produced. Gold for jewellery can be given a
range of hues depending on the metal with which is alloyed (white, red, blue,
green etc.). Colloidal gold is added to glass to colour it red or purple, and
metallic gold is applied as a thin film on the windows of large building to
reflect the heat of the Sun's ray. Gold electroplating is used to in the
electronic industry to protect their copper components and improve their
solderability.
Gold in the environment
Glod
is widely distributes on the earth at a background level of 0.03 g/1000 kg (0.03
ppm by weight). Its interness and its high density causes it to concentrate in
streambeds, either in small flakes or in larger nuggets, from which it may be
recovered by panning. It is found free in nature and associated with quartz,
pyrite and other minerals.
Most gold is mined and comes from gravels and quarts veins or is associated
with pyrites deposits. Two
thirds of the world's supply comes from South Africa, and
2/3 of USA production is from South Dakota and Nevada.
Other main mining areas are Canada and Russia. Gold is found in sea water, but
no effective economic process has been designed (yet) to extract it from this
source. World production is around 2500 tonnes per year, but reserves are
estimated to be ten of thousand of tonnes.
Back to
the periodic table of elements
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