Gold chemistry, Characteristics of gold, applications of gold

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Gold: 

source: Internet


Gold is a chemical element. The symbol of gold is Au and atomic number 79, making it one of the higher atomic number elements that occur naturally. In a pure form, it is a bright, slightly reddish yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal and a group 11 element. It is one of the least reactive chemical elements and soil under standard conditions. Gold often occurs in free elemental form, as grains, in rocks, in veins. It occurs in a solid solution series with the native element silver, naturally alloyed with other metals like copper and palladium, and also mineral inclusions such as within pyrite. Less commonly, it occurs in minerals as gold compounds, often with tellurium(gold tellurides).

Gold is resistant to most acids, though it does dissolve in aqua regia ( a mixture of nitric acid and hydrochloric acid), which forms a soluble tetrachloroaurate anion. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to refine gold and to confirm the presence of gold in metallic objects giving rise t the term acid test. Gold also dissolves in alkaline solutions of cyanide, which are used in mining and electroplating. Gold dissolves in mercury-forming amalgam alloys, but this is not a chemical reaction.

A relatively rare element, gold is a precious metal that has been used for coinage, jewelry, and other arts throughout recorded history. In the past gold standard was often implemented as a monetary policy.

Characteristics of GOLD:

Gold is the most malleable of all metals. It can be drawn into a wire of single-atom width and then stretched considerably before it breaks. Such nanowires distort via formation, reorientation, and migration of dislocation and crystal twins without noticeable hardening.
Gold has a density of 19.3 g/cm3, almost identical to that of tungsten at 19.25 gm/cm3, as such, tungsten has been used in counterfeiting gold bars, such as plating a tungsten bar with gold.

Color:
Whereas most metals are grey or silvery white, gold is slightly reddish yellow. This color is determined by the frequency of plasma oscillations among the metal's valence electrons, in the ultraviolet range for most metals but in the visible range for gold due to relativistic effects affecting the orbitals around gold atoms.

Origin:

Gold is thought to have been produced in supernova nucleosynthesis and from the collision of neutron stars, and to have been present in the dust from which the solar system formed.

Other applications:

Jewelry


Because of the softness of pure(24k) gold, it is usually alloyed with base metals for use in jewelry, alternating its hardness and ductility, melting point, color, and other properties. Alloys with lower karat ratings, typically 22k, 18k, 14k, or 10k, contain a higher percentage of copper or other base metals or silver or palladium in the alloy. High karat white gold alloys are more resistant to corrosion than are either pure silver or sterling silver.

Medicinal uses:

In Medieval times, gold was often seen as beneficial for health, in the belief that something so rare and beautiful could not be anything but healthy.
In the 19th century, gold had a reputation as an anxiolytic, therapy for nervous disorders.
Medicinal applications of Gold and its complexes have a long history dating back thousands of years. Several gold complexes have been applied to treat rheumatoid arthritis, the most frequently used being aurothiomalate, aurothioglucose, and auranofin.
Both gold(I) and Gold(III) compounds have been investigated as possible anti-cancer drugs.

The physical properties of gold:

  • It's a soft ductile metal.
  • It has a very high melting point and boiling point.
  • It is a good conductor of electricity and heat.
  • It is a Nobel metal.
  • It is very heavy and dense.
  • It is highly reflective.

The Chemical properties of Gold:

  • It is almost totally immune to decay 
  • It is not very useful in any industrial/chemical processes which use it up 
  • It is easy to store cheaply for long period.

Reactions of Gold:

Reactions with air
Under normal conditions, gold will not react with air.

Reactions with water
Gold does not react with water, under any circumstances.

Reactions with halogens
Gold reacts with chlorine and bromine to form trihalides and with iodine to form a monohalide.
  
2Au(s) + 3Cl2(g)→2AuCl3(s)

2Au(s) + 3Br2(g)→2AuBr3(s)

2Au(s) + I2(g)→2AuI(s)

Reactions with acids

Gold can be dissolved with a mixture of hydrochloric acid (HCl) and concentrated nitric acid (HNO3), in a ratio of 3:1. This combination is known as aqua regia, "royal water".

Reactions with bases:

Gold will not react with aqueous bases.






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