What is Gold

Gold (prounounced as GOLD) is a lustrous and valuable metal belonging to the family of noble metals. Denoted by the chemical symbol Au, it is does not react with other elements or compounds. Pure gold is designated as 24 carats that’s soft in nature, and hence alloyed with other metals. It has 35 isotopes with mass numbers ranging from 171 to 205 of which only Au-197 is stable ^{[1, 2]}.

Where is Gold Found

It can be naturally found in the free form as well as associated with calcite, quartz, silver, tellurium, lead, zinc, and copper in veins and alluvial deposits. Every year about 1500 tonnes of gold are mined of which two-thirds comes from South Africa and Russia ^{[1, 2]}.

History

Origin of its Name: It’s derived from the Anglo-Saxon word ‘gold’ and the Sanskrit word ‘jval’ ^[2].

Who First Discovered Gold: Since the metal is known for more than 5500 years, nobody knows about its original discoverers ^[1].

When, Where, and How was it Discovered

There are no records of gold’s actual year of discovery since it existed during the prehistoric times in the form of nuggets in river and stream beds. In 2000 BC, the Egyptians actively mined the metal that was obvious from the objects found in the graves of the royal family.

By 640 BC, gold coins made by alloying Au with silver began to circulate in the Kingdom of Lydia. It was only during the reign of King Croesus when pure coins were minted ^[1].

Identification
Atomic number	79 [1]
CAS number	7440-57-5 [1]
Position in the periodic table [1]	Group	Period	Block
	11	6	d

Classification, Properties and Characteristics of Gold

General Properties
Relative atomic mass	196.967  [1]
Atomic mass/weight	196.967  atomic mass units [5]
Molar mass/Molecular weight	196.967 g/mole [6]
Mass Number	197
Physical Properties
Color/physical appearance	Golden yellow [1]
Melting point/freezing point	1064.18°C (1947.52°F) [1]
Boiling point	2836°C (5137°F)  [1]
Density	19.3 g/cm3 [1]
Standard/Natural state at room temperature (solid/liquid/gas)	Solid [1]
Malleability	Yes [2]
Ductility	Yes [2]
Hardness	2.5 Mohs [5]
Specific heat capacity	0.128 J g-1K-1 [4]
Chemical Properties
Flammability		Not flammable
Oxidation state/Oxidation number		−1, +1, +2, +3, +5 [1]

Atomic Data of Gold (Element 79)

What are the Common Uses of Gold

• Several types of jewelry are either made from pure gold or alloyed with other metals like copper, silver, palladium, and platinum ^[1]. The alloys are also used as dental fillings ^[2].
• Since Au is malleable, it can be beaten into thin sheets called gold leaf and used in gilding to decorate interiors, architecture ornaments, and craft items ^[2].
• In some countries, coins made of gold are used as a legal tender and monetary exchange medium ^[1].
• Artificial limb joints, watch gears, junk jewelry, and electrical connectors are plated with the metal to protect against corrosion. A good conductor of electricity as well, it is used in coating electrical copper components ^[1].
• It is made into thin wires for making circuits in computer chips and motherboards ^[1].
• Colloidal suspension of Au nanoparticles plays the role of industrial catalysts in large-scale chemical reactions to produce compounds like polyvinyl acetate ^[1].

Are There Any Toxic Effects of Gold

When administered into body as a part of therapy, excessive accumulation may lead to poisoning, resulting in kidney failure, liver inflammation, platelet dysfunction, nausea, and mouth ulcers ^[6].

Interesting Facts

• The symbol of the metal originates from the Latin word for gold called aurum ^[2].
• About 4 grams of Au is present in 1,000,000 tons of water whose recovery cost would exceed the price of the metal itself ^[1].
• Gold leaf is 400 times thinner than a human hair ^[2].

Gold Price

The cost of pure (24 carat) gold may vary between $38 and $40 per gram.

References
1. http://www.rsc.org/periodic-table/element/79/gold
2. https://education.jlab.org/itselemental/ele079.html
3. https://pubchem.ncbi.nlm.nih.gov/compound/gold
4. https://www.chemicool.com/elements/gold.html
5. Lbma.org.uk
6. https://www.dovemed.com/diseases-conditions/gold-toxicity/