Chemistry

The Chemical Properties of Gold



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Gold has been one of the most valuable and coveted metals for as long as man has dug it up from the earth. Not only is it strikingly beautiful in its pure form, but it also has many interesting chemical and physical properties that make it quite unique from other metals.

The name gold is derived from the Anglo-Saxon word "geolo", which not surprisingly means "yellow". On the Periodic Table of the Elements, the chemical symbol for gold is AU. As with many symbols used on the Periodic Table, this comes from the Latin name "Aurum", meaning "Glowing Dawn", or "Shining Dawn" depending on your particular translation.

The distinctive yellow hue of gold is most obvious when the gold is pure. When mixed with other chemical impurities, gold can take on tinges of green, red, black and red.

Chemical and physical properties

As with most metals, gold is both ductile and malleable. Being ductile means that it can be dawn in to thin wires. Malleability means that it can be pounded in to thin sheets and still maintain its strength. Gold is so malleable that it can be beaten in to sheets so thin they are see-through.

Gold has an amazing ability to transfer both heat and electricity. Only silver and copper are better at doing this. Because of these features, gold is often used in electronics. Thin wires of gold can conduct both heat and electricity in a wide variety of circuits.

The melting point of gold is very high - 1064 Celsius. Needless to say, by the time solid gold melts in to a liquid, you wouldn't want to be touching it.

If you were to continue heating liquid gold to its boiling point, you wouldn't expect it to begin to boil until it reached a whooping 2860 degrees Celsius. For comparison, remember that by definition water boils at 100 degrees Celsius. Think of how fast you could cook pasta in a bowl of boiling gold! (Do not try this at home, even if you have that much gold. It's meant to be a joke.)

Gold is one of the most dense metals in existence. Each cubic centimeter of pure gold weighs about 19.3 grams. That may not mean a lot, but trust me when I say that its a lot of weight for a very small volume. Gold is more dense than lead, copper or silver.

Gold is relatively soft compared to other metals. In theory you can scratch pure gold by biting it, although your dentist may not suggest this is a good idea. To make gold harder to scratch, you can make alloys with other metals. An alloy is a metal that has intentionally had impurities added to it. Color of gold can be altered as well as hardness by alloying. This is commonly done in jewelry, as you may not want your ring or necklace to be easily marked by people trying to bite them.

If swallowed, gold is non-toxic. It can be ingested and will just pass right though your gut. On occasion it is used in some very posh foods and drinks in small amounts. As a general rule however, it is not a good idea to try and eat your favorite set of earrings. There is always a chance they could get lodged in your intestines if they are too large - not to mention that there are cheaper and more nutritious snacks available.

Reactivity with other elements

Gold is very resistant to corrosion and reacting with other elements. It does not tarnish or rust in the presence of air. This property is one of the reasons it is so popular in jewelry - you don't have to worry about gold looking bad a few years after you buy it.

If you do want to destroy a sample of gold in a chemical reaction, you are going to need some pretty toxic chemicals. Both gaseous chlorine and flourine will react with gold. It should be pointed out that both of these elements in their gaseous form will not only destroy gold, but also your lungs. As they say on television, "Do not try this at home."

If you are looking for a liquid that will destroy gold, you aren't going to have many more options. Gold can sit quite comfortably in water forever without rusting. Alkaline solutions are harmless to gold. Most acids won't damage gold, not matter how concentrated. There is one key exception however, an acid called by its latin name - aqua regia.

Aqua regia means "Kingly Water", and it named thus for its ability to dissolve gold. It is a mixture of hydrochloric acid and nitric acid. It's nasty stuff and certainly not something you want to play with causally.

If you don't happen to have a bottle of aqua regia laying around the house, you can also use sodium or potassium cyanide to dissolve gold. OK, those chemicals aren't very common either, but that's not the point.

Pure nitric acid will not dissolve gold, but will attack other metals. This provides a way of determining if a metal is pure gold or not. If you put your sample of unknown metal in a bit of nitric acid and the sample metal dissolves, it wasn't gold.

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