Gold has an atomic number of 79. Its name is from the Sanskrit word Jval and the Anglo Saxon word for gold. Its chemical symbol, Au, is from the Latin word for gold, aurum, which means yellow. Use of gold dates back as far in human history as mankind's first civilizations. It has been used in coins, crowns, jewels, metals, and other objects of value. It has also been used in medicine. Gold weight is expressed in names like bars, meaning heavy. It is still used in dental crowns and in electrical points.
The atomic weight of gold is 196.966569 and its melting point is 1337.33 K (1064.18C or 1947.52F). Its boiling point is 3129 K (2856C or 5173F), its density is 19.282 grams per cubic centimeter and it is a solid at room temperature. It is classified as a metal in period six and group eleven.
Known in civilization for over five thousand years, gold is found in isolation in the earth, or in mines alongside silver, quartz, calcite, lead, tellurium, zinc, or copper. It is a very malleable and ductile metal, and can be rolled into a sheet four hundred times thinner than a human hair.
Because gold is soft, it is frequently alloyed with other metals, for instance, silver, copper, platinum, or palladium. These alloys are used in jewelry, dental fillings and coins. The amount of gold in an alloy is measured as carats. A carat is equal to one part in twenty-four, so an 18 carat ring has 18 parts gold and six parts other metal.
Gold conducts heat and electricity well, as do most metals, and it does not tarnish. For this reason, it is used to make electrical connectors and printed circuit boards. Gold reflects infrared radiation and can shield spacecraft from the sun, as well as skyscrapers. Mirrors coated with gold are used in telescopes, to make them more sensitive to infrared light. Gold is also used in the preservation of photographs by replacing the silver atoms with gold, to protect the image.
Gold has long been used in medicine. Records show gold usage in Egyptian medicine. It is used as a homeopathic remedy particularly for heart conditions. The mental picture of a person needing the homeopathic remedy Aurum is a sense of responsibility, and holding on to power. Aurum patients have a fear of heights, of falling, of fire and the dark. A radioactive isotope of gold, gold-198 is in use for cancer treatments, and gold sodium thiosulfate is used to treat arthritis.