This metal has been known since prehistoric times. Gold is a soft metal with a characteristic yellow colour. It is the most malleable and ductile of any element. It is unaffected by air, water, alkalis and acids, with the exception of “aqua regia”, HNO3/HCl. The fact that it is chemically unreactive means that it is often found in its natural state. It is a good thermal and electrical conductor and has excellent reflective properties to both light and infrared. It has an abundance in the earth’s crust of 0.0011 ppm. Most of the metal is retained for use as bullion reserves, but some is used within the electronics and jewellery industries, where it is frequently alloyed with other elements to improve the mechanical properties of the metal (e.g. copper and silver). Other uses for the metal are as a heat reflecting coating for glass as well as as a decorative medium.

Key Properties

Atomic Properties Atomic number 79 Atomic radius - Goldschmidt ( nm ) 0.144 Atomic weight ( amu ) 196.9665 Crystal structure Face centred cubic Electronic structure Xe 4f14 5d10 6s1 Photo-electric work function ( eV ) 4.8 Thermal neutron absorption cross-section ( Barns ) 98.8 Valences shown 1,3 Ionisation Potential No. eV 1 9.22 2 20.5 Natural Isotope Distribution Mass No. % 197 100 Electrical Properties Temperature coefficient ( K-1 ) 0.0040 @ 0-100 Electrical resistivity ( µOhm.cm ) 2.20 @ 20 Thermal emf against Pt (cold 0°C - hot 100°C) ( mV ) +0.74 Mechanical Properties Material condition Soft Hard Polycrystalline Bulk modulus ( GPa ) 171 Hardness - Vickers 20-30 60 Poisson's ratio 0.42 Tensile modulus ( GPa ) 78.5 Tensile strength ( MPa ) 130 220 Yield strength ( MPa ) 205 Physical Properties Boiling point (°C ) 3080 Density ( g.cm-3 ) 19.30 @ 20 Melting point (°C ) 1064.4 Thermal Properties Coefficient of thermal expansion ( x10-6 K-1 ) 14.1 @ 0-100 Latent heat of evaporation ( J.g-1 ) 1738 Latent heat of fusion ( J.g-1 ) 64.9 Specific heat ( J.K-1.kg-1 ) 129 @ 25 Thermal conductivity ( W.m-1.K-1 ) 318 @ 0-100