There's GOLD in them thar hills!

Sam Mah with a large rock rich in gold.

Gold is an amazing metal.  We all understand that it is valuable, and most of us will have something made of gold, even if it's not 24 karats (pure gold, not a gold alloy).  But few, relatively speaking, understand exactly why gold is considered valuable, or what some of its more important physical and chemical characteristics are.  Consider the following:

Gold does not react with much.  There are a few things that do combine with gold in nature, such as tellurium and pure halogens (fluorine and chlorine).  In small scale mining operations mercury is added to crushed ore where it forms an amalgam with the metals, including any gold.  It is recovered later by heating (video here).  This is why gold is found in pure form, it generally doesn't combine with anything.  It will not react with acids (except for aqua regia - a concentrated mixture of nitric and hydrochloric acid), bases, water, sulfur compounds, and the list goes on.

Gold is heavy for its size; this is called density.  Gold, in fact, is about 19.3 times heavier than water for its voluem.  Why is this important?  If you have a liter of water, it weighs 1000 grams, 1 kg, or about 2.2 pounds.  One liter of gold weights 19,300 grams, 19.3 kg, or about 42.5 pounds.  It is this high density which allows one to extract gold from stream beds by panning.  It goes to the bottom and stays there.  If gold is present in an area where a stream cuts through it will erode away with neighbouring bedrock and end up in the riverbed.  It is so dense that it does not move as far as other rocks do over time and you can pan for it; it will be modestly close to whatever the source was.

The density of gold brings up an important movie consideration.  Think of thieves taking a box of gold.  Let's say the box has a capacity of 1080 cubic inches (18" x 10" x 6").  That converts to 17,712 ml, which is 17.7 liters of volume.  Remember the density of gold?  That box would weigh 342 kilograms or about 752 pounds.  You, me,  and all of our immediate neighbours would have a hard time lifting that box together, little lone one bad guy in a hurry.  But it makes a good visual presentation, even if the science is way off.

Gold is perhaps the most malleable metal on the planet.  Malleability is being able to pound a substance into a sheet.  Hit charcoal with a hammer and it shatters.  Zero malleability.  Hit playdough with the same tool and it squashes nicely.  Gold is more like that.  It doesn't even have to be hot like iron does if you want to work it.  Hit a pure gold ball and it gets a bit flatter.  Repeat and it continues getting thinner and thinner.  In fact, gold is so malleable that you can create a sheet of it only 400 atoms thick.  One ounce of gold can be flattened into a sheet over 9 square meters (almost 100 square feet) in size.  This is what the scientist Rutherford used in his experiment to hypothesize that the center of an atom was small and dense.  An atom, as it turns out, is mostly empty space.

How much gold is there in the world?  It turns out gold is a fairly rare metal.  You could fill an Olympic sized swimming pool with every gram of gold ever found, and still have room left over.   Have a look at this website; I found it fascinating. 

OK - last thought.  On top of all the other amazing properties of gold, here is another one.  Gold is one of the best conductors of electricity in the world.  Although copper and silver also rate very high, gold's resistance to tarnishing makes it valuable in certain electronics.  Your cell phones and computer motherboards all likely have gold in them.  Lots of devices do.  This is one of the reasons why it is important to recycle them.  There are other metals too, including some heavy metals which are bad for the environment.  Have a look at this article on gold recycling.

Thanks for reading.