Gold

Element Gold

It is a chemical element with the symbol Au (from Latin: aurum) and atomic number 79, making it one of the higher atomic number elements that occur naturally.
In its purest 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 is solid under standard conditions.
Gold often occurs in free elemental (native) form, as nuggets or grains, in rocks, in veins, and in alluvial deposits.
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 to 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.

Gold has only one stable isotope, 197 Au, which is also its only naturally occurring isotope, so gold is both a mononuclidic and monoisotopic element.
Thirty-six radioisotopes have been synthesized, ranging in atomic mass from 169 to 205. The most stable of these is 195Au with a half-life of 186.1 days.