Gold is a chemical element whose atomic number is 79. It is located in group 11 of the periodic table. It is a soft golden yellow precious metal. Its symbol is Au (from the Latin aurum, 'bright dawn'). In addition, it is one of the most appreciated metals in jewelry for its physical properties, having low alterability, being very malleable, ductile and shiny, and valued for its rarity, being a metal that is difficult to find in nature.

It is a soft, shiny, yellow, heavy, malleable and ductile transition metal. Gold does not react with most chemicals, but is sensitive and soluble to cyanide, mercury, aqua regia, chlorine and bleach. This metal is normally found in its pure state, in the form of nuggets and alluvial deposits. It is an element that is created thanks to the extreme conditions in the collapsing core of supernovae. When the nuclear fusion reaction stops, the upper layers of the star collapse onto the stellar core, compressing and heating the matter to the point that lighter nuclei, such as iron, fuse to give rise to the nuclei. heavier metals (uranium, gold, etc.). One study suggests the planet's gold came from colliding neutron stars.

Primary gold deposits in the crust form from very hot, metasomatic gasses and liquids rising from the Earth's interior, which are moved to the surface through faults in the Earth's crust.

Gold exhibits a crude yellow. It is considered the most malleable and ductile metal known. One ounce (31.10 g) of gold can be molded into a sheet covering 28 m². As it is a soft metal, alloys with other metals are common in order to provide hardness.

In addition, it is a good conductor of heat and electricity, and is not affected by air or most chemical agents. It has a high resistance to chemical alteration by heat, humidity and most corrosive agents, and is thus well adapted to use in coinage and jewelry.

It is a very dense metal, with a high melting point and high electron affinity. Its most important oxidation states are 1+ and 3+. It is also found in the 2+ oxidation state, as well as higher oxidation states, but is less common. The stability of gold species and compounds with oxidation state III, compared to their group homologues, must be reasoned.

Gold is extremely inactive. It is unaltered by air, heat, humidity and most chemical agents, although it dissolves in mixtures containing chlorides, bromides or iodide. It also dissolves in other oxidizing mixtures, in alkaline cyanides and in aqua regia, a mixture of nitric acid and hydrochloric acid. Once dissolved in aqua regia, chloroauric acid is obtained, which can be transformed into metal gold with sodium disulfite. Gold becomes soluble when exposed to cyanide.

In jewelry, different high gold alloys are used to obtain different colors, namely:

■ Blue gold = 75% gold and 25% iron.

■ Gray gold = 75% gold, 15% nickel and 10% copper.

■ Red gold = 75% gold and 25% copper.

■ Rose gold = 75% gold, 5% silver and 20% copper.

■ Yellow gold = 75% gold, 12.5% silver and 12.5% copper.

■ Green gold = 75% gold and 25% silver.

■ White gold = 75% gold, 16% palladium and 9% silver.

It is worth mentioning that the color obtained, except in white gold, is predominantly yellow, that is, “green gold” is not green, but yellow with a greenish hue.