Gold is a metallic element, its chemical symbol is Au, and its atomic number is 79.
The simple substance (free form) of gold, commonly known as gold, is a popular precious metal, which has been used as currency, preservation and jewelry for many centuries. In nature, gold exists in the form of simple substance in gold nuggets or rocks, underground veins and alluvium. Gold is also one of the currency metals. Gold, a simple substance, is solid at room temperature, with high density, softness, brightness, corrosion resistance and the highest ductility and ductility among known metals. This is a red-yellow metal, soft and tough. Crystal structure: the unit cell is a face-centered cubic unit cell, and each unit cell contains 4 metal atoms.
Gold is a transition metal, which can form trivalent and monovalent positive ions after dissolution. Gold does not react with most chemicals. The common valence is generally zero, but it can be eroded by chlorine, fluorine, aqua regia and cyanide. Gold can be dissolved by mercury to form amalgam (but this is not a chemical reaction); Nitric acid can dissolve silver and base metals, but it cannot dissolve metal gold. The above two properties become the basis of gold refining technology, which are called "separate casting" and "separate casting" respectively.
Gold is the most malleable and malleable metal. A gram of gold can be cut into one square meter, or an ounce of gold can be cut into 300 square feet. Gold leaves can even be thinned to translucent, and the light passing through them will appear green and blue, because gold has strong reflection ability to yellow and red light.
Pure gold is tasteless because it is very resistant to corrosion (the taste of other metals comes from metal ions). In addition, the density of gold is quite high, and the weight of one cubic meter of gold is 19.320 tons. Comparatively speaking, the density of lead is 1 1340 kg/m? The element with the highest density is osmium, and its density is 2266 1 kg/m? .
Its chemical properties are inactive, and it can only be dissolved in corrosive substances such as aqua regia, selenic acid and perchloric acid. Its valence is generally zero, and it is a transition metal, which can form trivalent and monovalent positive ions (such as gold chloride, gold oxide, gold hydroxide, etc. ) After dissolution. Gold will not react with most chemicals, but will be corroded by chlorine, fluorine, aqua regia and cyanide. Gold can be dissolved by mercury to form amalgam (but this is not a chemical reaction); Nitric acid can dissolve silver and alkali metals, but not gold. The above two properties become the basis of gold refining technology, which are called "adding silver to divide gold" and "separating gold from silver" respectively. In addition, nitric acid can be used to identify whether an object contains gold. This ancient method is also the etymology of the English proverb "acid test", which means to test whether a substance is worthy of its name by "the standard for testing gold".
The valence of gold is usually zero, but there are also+1 (positive monovalent gold) and +3 (positive trivalent gold). By adding other metals as reducing agents, gold ions in the solution can be easily reduced and precipitated into simple gold, thus forming gold nuggets.