Once upon a time in a land far, far away, there only existed four basic elements: earth, water, air and fire. The ancient Greeks believed that these four elements constituted everything – in varying amounts and in varying proportions.
It’s extraordinary how well these classical elements correlate with the common four states of matter. We can match earth with solid, water with liquid, air with gas, and fire with plasma. There are of course other (more exotic) states of matter which emerge under extreme conditions, but it would be a little excessive to expect the ancient Greeks to have observed Bose-Einstein condensates.
Aristotle additionally suggested a fifth element, aether, theorised to be heavenly matter out of which stars are made.
Other civilisations at the time also formulated their own system of classical elements. The ancient Chinese Wu Xing system, for instance, consisted of wood, fire, earth, metal and water, each of which interacted with one another in a system similar to that of rock-paper-scissors.
Fast forward to the Middle Ages and humans have already identified several of the elements we list in the periodic table of chemical elements. Between classical antiquity and the Middle Ages, there were believed to exist nine elements: two non-metals and seven metals, a surprising conclusion due to the abundance of non-metals we see in our daily lives (in woods, in plastics and in fabrics, to name a few).
The first non-metal is carbon. This is what one would expect – carbon is an abundant element on Earth and it makes up approximately 18% of the human body. We breathe out carbon dioxide. When we burn fuel, we’re left with carbon. Carbon is a key element in the majority of biological and chemical processes. In fact, carbon is so important that we have an entire field of chemistry dedicated to studying carbon-based chemistry, which we call organic chemistry. The bearing of carbon on human processes leads us to believe that humans are carbon-based lifeforms.
The second non-metal is, surprisingly, sulphur. This is because sulphur is abundant in its native form on the surface of the Earth and also in many minerals. Sulphur is mentioned in texts as early as the Bible through its archaic name, brimstone, often with reference to wrath of God: Then the LORD rained on Sodom and Gomorrah brimstone and fire from the LORD out of heaven; (Genesis 19:24).
The seven metals in antiquity are gold, silver, mercury, copper, iron, tin and lead. At first there appears to be no pattern besides the fact they’re all metals which even the most scientifically illiterate will have heard of! After a little scientific analysis, however, a correspondence emerges: all are metals which tend to have a high abundance, a low melting point, or are easily extracted from their respective ores (or all of the above). Gold and silver, although rare, are very unreactive and occur frequently as elemental gold and silver and not as ores. The other metals are able to be extracted from their ores using primitive, low-energy extraction methods.
This little dose of the history of chemistry also links in to why we have seven days in a week, an odd choice of number. The seven days are attributed to the seven heavenly bodies – the seven visible astronomical objects in the night sky. We could easily match Sunday with the Sun, Monday with the Moon, and perhaps Saturday with Saturn. The other ones are more of a guessing game if one has no background in classics or astronomy: Tuesday goes with Mars, Wednesday goes with Mercury, Thursday goes with Jupiter, and Friday goes with Venus.
Each metal was associated with each of the heavenly bodies. You’ve probably spotted that gold goes with the Sun and silver goes with the Moon. In summary:
From the classical elements to the metals in antiquity, the journey of discovering chemical elements has been a successful and interesting one. Today, the periodic table meticulously tabulates the 118 known chemical elements and counting.