Gold is a chemical element (Au symbol) of atomic number 79 (79 protons and 79 electrons) that is situated in group eleven (IB) of the periodic table, and atomic mass 197 u. In nature, gold is produced from the collision of two neutron stars. Gold is widely used in jewellery, industry and electronics as well as value reserve.

It is a bright, yellow, dense, malleable, ductile (trivalent and univalent) transition metal that does not react with most chemicals but is sensitive to chlorine and bromine. At room temperature, it is in the solid state. This metal is normally in the pure state, in the form of nuggets and alluvial deposits, being one of the metals traditionally used to mint the coin. It is so easily handled and malleable that, with only one gram of gold, it is possible to obtain a 3-kilometer-long and 0.005-millimeter-diameter wire, or a 70-cm wide, 0.1-micrometer-thick square blade.

Pure gold is too soft to use. For this reason, it is usually hardened forming metal alloy with silver and copper. Gold and its various metal alloys are widely used in jewellery, in the manufacture of coins and as a monetary standard in many countries. Due to its good electrical conductivity, corrosion resistance and a good combination of physical and chemical properties, it has several industrial applications.