Pure gold is yellow, which makes it quite unlike other metals, but in every other way it is a typical metal.
Like other metals it is…
- malleable – it can be bent into shapes without cracking
- ductile – it can be drawn out into wires or rolled out into foil
- shiny – unlike other metals, gold retains its shine because it does not react with the chemicals in air that make other metals lose their shine over time
- a good conductor of both heat and electricity
- sonorous – they produce a ringing sound when they are hit with an object
- they tend to have a high density
- they tend to be hard
- they tend to have high melting and boiling points
Gold is the most malleable and ductile metal of the lot, which means it can be rolled into incredibly thin sheets (called gold leaf). This is usually about 0.1 µm thick.
1 g of gold can be made into a sheet of gold leaf with an area of 1 m2. Gold is very dense; 1 cm3 of gold has a mass of 19.3 g. It melts at 1064°C which is rather higher than we can manage with a Bunsen in the lab.
Gold atoms have 79 protons in their nucleus so are surrounded by 79 electrons. Most gold atoms also have 118 neutrons in their nucleus as well as the protons. This means that a gold atom has a relative atomic mass of 197; therefore an atom of gold is 197 times heavier than an atom of hydrogen.
Gold is very unreactive so it can be found as nuggets of pure gold in riverbeds and seams of pure gold within certain rocks. It is also present in an invisible form within other rocks as gold ore. Although gold will not dissolve in most acids (even nitric acid which can dissolve copper and silver) it can be dissolved out of its ore with an alkaline solution of potassium cyanide. All the gold ever extracted on Earth (205,000 tonnes) would form a cube with edges about the length of a cricket pitch.
As well as making coins, jewellery and ornaments, gold is used in the electronics industry. Mobile phones, computers and other hi-tech devices all contain a little gold performing some vital role where electrical conductivity and resistance to corrosion are important.
Questions…
- Gold is unlike most other metals because it isn’t silvery/grey in colour. Suggest another.
- What is the approximate highest temperature that a Bunsen can achieve in our labs?
- Name a metal that would not be described as hard.
- Name a metal with a low melting point.
- Name a metal with a higher density than gold.
- How long is a cricket pitch? (Choose your own units but metric ones would be prudent!)
- [Extension] To 1 sig fig, what would be the volume in cm3 of a 1 g cube of gold?
1. Copper is also not silvery or grey, this and gold are the only two such metals
2. Around 2700 degrees Celsius this is the approximate temperature of a blue flame
3. Potassium would not be described as hard.
4. Potassium has a low melting point.
5. platinum is pretty dense, denser than gold
6. In the seventeenth century, surveyors used a physical length of chain, with 100 links, as their method of reliable measurement. Being about the right length for the newly invented game of cricket, the pitch was defined as being one chain, or 22 yards! (google, but quite interesting!).
7.(1/19.3 = 0.05cm3)
Thank you for another interesting post!
Q1 – in the words of Yoda “There is another!” Good!
Q2 – that might be somewhat high for a lab burner using methane and air. A good rule of thumb is that you can just about melt aluminium in the roaring blue flame.
Q3 – excellent
Q4 – indeed it does (about 64 °C)
Q5 – good. There are only a couple of metals denser than platinum.
Q6 – chains, furlongs, yards – all good imperial units.
Q7 – Well done. It will be good to get used to rounding things off to make the maths easier e.g. 1/20 = 0.05 cm3
Great stuff – well done!