Gold
Gold, symbol Au (from Latin aurum, “gold”), soft, dense, bright yellow metallic element. Gold is one of the transition elements of the periodic table (see Periodic Law ); its atomic number is 79. PROPERTIES Pure gold is the most malleable and ductile of all the metals. It can easily be beaten or hammered to a thickness of 0.000013 cm (0.000005 in), and 29 g (1.02 oz) could be drawn into a wire 100 km (62 mi) long. It is one of the softest metals (hardness, 2.5 to 3) and is a good conductor of heat and electricity. Gold is bright yellow and has a high luster. Finely divided gold, like other metallic powders, is black; colloidally suspended gold ranges in color from ruby red to purple (see Colloid ). Gold is extremely inactive. It is unaffected by air, heat, moisture, and most solvents. It will, however, dissolve in aqueous mixtures containing various halogens such as chlorides, bromides, or some iodides. It will also dissolve in some oxidizing mixtures, such as cyanide ion with oxygen,