Gold
Au
Heat, moisture, oxygen, and most corrosive agents have very little
chemical effect on gold, making it well-suited for use in coins and
jewelry.
The History Says
Gold is mentioned several times in the Old Testament. The south-east
corner of the Black Sea was famed for its gold. Exploitation is said
to date from the time of Midas, and this gold was important in the
establishment of what is probably the world's earliest coinage in
Lydia between 643 and 630 BC.
The Present Scenario
The gold isotope Au-198, is used in some cancer treatments and for
treating other diseases.
Gold
is a metallic element. Its atomic number is 79. It is soft, shiny,
yellow, dense, malleable and ductile. It does not react with most
chemicals but is attacked by chlorine, fluorine and aqua regia. This
metal occurs in the form of nuggets or grains in rocks. It is is also
found in alluvial deposits.
Gold is measured by troy weight and by grams. If alloyed with other
metals, a term 'carat' or 'karat' is used to indicate the amount of
gold present. Pure gold is 24 carats.
Physical Properties of Gold
| Phase |
Solid |
| Density (near room temperature) |
19.3 g/cm3 |
| Liquid density at melting point |
17.31 g/cm3 |
| Melting point |
1337.33 K (1064.18°C,
1947.52°F) |
| Boiling point |
3129 K (2856°C, 5173°F)
|
| Heat of fusion |
12.55 kJ/mol |
| Heat of vaporization |
324 kJ/mol |
| Heat capacity |
(25°C) 25.418 J/(mol-K) |
Atomic Properties of Gold
| Crystal structure |
Cubic face centered |
| Oxidation states |
3, 1 (amphoteric oxide) |
| Electronegativity |
2.54 (Pauling scale) |
| Ionization energies |
1st: 890.1 kJ/mol
2nd: 1980 kJ/mol |
| Atomic radius |
135 pm |
| Atomic radius (calc.) |
174 pm |
| Covalent radius |
144 pm |
| Van der Waals radius |
166 pm |
Characteristics of Gold
Gold is yellow in color but can also occur in black or ruby when it
is finely divided. The colloidal solutions are intensely colored and
are often purple. Gold's plasmon frequency, lying in visible range,
results in colors. It absorbs blue light and causes the red and yellow
light to be reflected.
Gold is most malleable and ductile. One gram can be beaten into a
sheet of one square meter. It readily forms alloy with many other
metals. With copper it yields redder metal, blue with iron, silver
produces green, aluminium-purple and platinum-white. Native gold
contains generally 8-10% silver.
Gold is a good conductor of both heat and electricity. It is not
affected by air and most regents. Heat, moisture, oxygen, and most of
the corrosive agents have very little chemical effect on gold.
Halogens chemically alters gold and aqua regia dissolves it.
Uses of Gold
- Gold
and its ally are often used in jewelry, coinage and a standard for
monetary exchange in many countries.
- Due
to its high electrical conductivity and resistance to corrosion, it
is used as industrial metal.
- It
is made into thread and used in embroidery.
- It
performs a critical functions in computers, communications
equipment, spacecraft, jet aircraft engines and host of other
products.
- The
resistance to oxidation property, it is used as a thin layers
electroplated on the surface of electrical connectors to make sure
of good connection.
- It
is used in restorative dentistry.
- Colloidal
gold (a gold nanoparticle) is an intensely colored solution and is
used as gold paint on ceramics prior to firing.
- Chlorauric
acid is used in photography to tone silver image.
- Gold(III)
chloride is utilised as catalyst in organic chemistry.
- It
is used in awards.
- It
is used for protective coatings on many artificial satellites as it
is a good reflector of infrared and visible light.
- The
isotope of gold, Au-198 is used in some cancer treatments and for
other diseases.
- Gold
flake is used in sweets and drinks.
- White
gold serves as the substitute for platinum.
- Green
gold is used in specialized jewelry.
World Gold Markets
- London
as the great clearing house
- New
York as the home of futures trading
- Zurich
as a physical turntable
- Istanbul,
Dubai, Singapore and Hong Kong as doorways to important consuming
regions.
- Tokyo
where TOCOM sets the mood of Japan
- Mumbai
under India's liberalized gold regime
Major Gold Producing Countries
- South
Africa
- United
States
- Australia
- China
- Canada
- Russia
- Indonesia
- Peru
- Uzbekistan
- Papua
New Guinea
- Ghana
- Brazil
- Chile
- Philippines
- Mali
- Mexico
- Argentina
- Kyrgyzstan
- Zimbabwe
- Colombia
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