- 郭靖Lv 71 decade agoFavorite Answer
Gold is a metallic element with a characteristic yellow color, but can also be black or ruby when finely divided, while colloidal solutions are intensely colored and often purple. These colors are the result of gold's plasmon frequency lying in the visible range, which causes red and yellow light to be reflected, and blue light to be absorbed. Only silver colloids exhibit the same interactions with light, albeit at a shorter frequency, making silver colloids yellow in color.
It is the most malleable and ductile metal known; a single gram can be beaten into a sheet of one square meter, or an ounce into 300 square feet. Gold readily forms alloys with many other metals. These alloys can be produced to increase the hardness or to create exotic colors. Adding copper yields a redder metal, iron blue, aluminium purple, platinum metals white, and natural bismuth together with silver alloys produce black. Native gold contains usually eight to ten per cent silver, but often much more — alloys with a silver content over 20% are called electrum. As the amount of silver increases, the color becomes whiter and the specific gravity becomes lower.
Gold is a good conductor of heat and electricity, and is not affected by air and most reagents. Heat, moisture, oxygen, and most corrosive agents have very little chemical effect on gold, making it well-suited for use in coins and jewelry; conversely, halogens will chemically alter gold, and aqua regia dissolves it.
Common oxidation states of gold include +1 (gold(I) or aurous compounds) and +3 (gold(III) or auric compounds). Gold ions in solution are readily reduced and precipitated out as gold metal by the addition of virtually any other metal as the reducing agent. The added metal is oxidized and dissolves allowing the gold to be displaced from solution and be recovered as a solid precipitate.
Recent research undertaken by Frank Reith of the Australian National University shows that microbes play an important role in the formation of gold deposits, transporting and precipitating gold to form grains and nuggets that collect in alluvial deposits. 
The concentration of free electrons in gold metal is 5.90×1022 cm-3.
Gold has been known and highly valued since prehistoric times. It may have been the first metal used by humans and was valued for ornamentation and rituals. Egyptian hieroglyphs from as early as 2600 BCE describe gold, which king Tushratta of the Mitanni claimed was as "common as dust" in Egypt. Egypt and Nubia had the resources to make them major gold-producing areas for much of history. Gold is also mentioned several times in the Old Testament. The south-east corner of the Black Sea was famed for its gold. Exploitation is said to date from the time of Midas, and this gold was important in the establishment of what is probably the world's earliest coinage in Lydia between 643 and 630 BCE......(http://en.wikipedia.org/wiki/Gold)
- 1 decade ago