In his book, The Last Sorcerers, Richard Morris charts the path from alchemy to the periodic table. He describes how scientists and philosophers have tried for well over two thousand years to understand the nature of the universe, as well as its composition. According to the ancient Greek philosopher, Thales, there was only one fundamental elements—water. Although this seems ridiculous today, when one considers that when heated, water evaporates into mist, and when frozen it becomes solid, as well as having the ability to sustain life, it isn’t impossible to see why this idea seemed plausible. This theory then developed into one that was held to be true for over two thousand years—namely, that the four ‘roots of all’, or elements were earth, air, fire and water. Aristotle also added a fifth, which was supposed to be the substance from which heavenly bodies were made.
Alchemy was a fusion of Greek and Egyptian thinking. Egyptians had practiced many chemical processes, including metallurgy, for centuries, and had created many ‘recipes’ for chemical transformations, for example when cinnabar (mercury ore) was heated and was ‘transformed’ into a pool of liquid metal. The Egyptians knew of seven metallic elements: gold, silver, copper, tin, iron, lead and mercury, but the Greeks were unable to see them as distinct elements, choosing instead to categorise them as mixtures of the traditional four elements, earth, air, fire and water. These changes in the state of elements seemed to confirm to the ancient philosophers (scientists did not exist at that time) that transformation from one element to another was a possibility.
It was in the years between 640 and 720 that the Muslim scholars had Greek and Syrian texts translated into Arabic and so learned of the ideas of ancient philosophers, and also of alchemy, the name they gave to the collections of chemical recipes and techniques handed down from the Egyptian alchemists. It is in Arabic alchemy that the concept of the Philosopher’s Stone—a substance believed to turn base metals into gold—first appeared.
Arabic alchemy was only discovered in Europe in the 11th Century when texts were translated from Arabic into Latin. One Arabic alchemist in particular, Jabir ibn Hayyan (known as Geber) introduced a theory that all metals were simply mixtures of sulphur, mercury and arsenic (except gold which was just sulphur and mercury). Jabir’s theory was that gold contained the most mercury and the least sulphur, so other metals could be transformed into gold if ways were found to increase their mercury content.
Following the translations of the older Arabic texts into Latin, European alchemy began to grow in the 11th and 12th Centuries, and although was equally unsuccessful in finding the Philosopher’s Stone, did make the important discoveries of how to make strong sulphuric and nitric acids in the early 14th Century, and so they were able to dissolve most metals. Some alchemists became completely obsessed with their quest for the Philosopher’s Stone and devoted their lives to discovering how to turn base metals into gold, spending family fortunes in the process.
The Swiss-German physician and alchemist, Paracelsus, who was born in 1493 was the first to use the term ‘chemistry’. Despite many long-lasting myths suggesting he had discovered the secret of immortality and was a servant of the devil, he engaged in serious experimentation in order to learn new cures for illnesses and was the first to focus on the purity and quantities of the chemical compounds he created. He also made an attempt to classify different chemical substances based on the reactions they produced. In fact he was the first to clinically describe syphilis and put forward small quantities of mercury as a treatment for the disease, which remained the standard treatment until 1909.
Robert Boyle, the 17th Century English scientist, was the founder of modern chemistry, as distinct from the work of alchemists, dye makers and metallurgists, and by the time of his death in 1691, chemistry had grown out of natural philosophy into a science. He challenged, although was unable to disprove, the long-held theory of the four elements.
At the start of the 17th Century, there were 13 known elements, of which 9 (carbon, sulphur, iron, copper, silver, gold, tin, lead and mercury) had been known since classical times, while arsenic, antimony, bismuth and zinc were discovered between 1250 and 1500. Most of these known elements were relatively low melting-point metals, perhaps discovered through fires. In 1650, however, all the known elements were still believed to be mixtures of earth, air, fire and water, except for tin, which was thought to be a mixture of silver and lead.
The first new element to be discovered since 1500 was phosphorous, discovered by an alchemist attempting to make gold from urine. This discovery eventually led chemists to realise that if one new element had been found, there may perhaps be still more. The next element, 66 years later, was cobalt—first used to colour glass, and from which the metal was first extracted in 1735.
There followed a period of rapid discovery, with a total of 78 elements being discovered during the 18th and 19th Centuries.
By 1900, the question that was puzzling chemists was why there were so many elements.
It was, of course, Dimitri Mendeleev who discovered the periodic law—it couldn’t explain why there were so many elements, but did allow him to group together elements with similar properties, as well as predict the existence of elements that had not yet been discovered, along with their atomic weight and chemical and physical properties. There was at that time, 1865, no comprehensive textbook of chemistry in Russian, so he decided to write one. During the course of this work, he gave much thought to the fact that there was no guiding principle of chemistry. He felt that there must be an order to the 63 elements that were known at the time.
As he wrote, it seemed natural to him to group the elements together into those with similar properties. To help him do this, he created a card for each element, including its atomic weight and most significant properties, such as melting point, density and malleability. He ordered the cards according to their atomic weight, beginning with hydrogen, the lightest, and ending with uranium, the heaviest known at the time.
By pinning the cards on the wall, he noticed that the properties of the elements “were periodic functions of their atomic weights.” The same properties could be seen after every seven elements. Several of the elements, however, simply didn’t fit into his scheme—beryllium was thought to have an atomic weight of 14 at the time, which would have put it in a group with nitrogen and phosphorus, so he took a leap of faith and changed the atomic weight to 9, which put it into the magnesium family, where it seemed to fit. He did the same with tellurium, moving it from 128 to somewhere between 123 and 126, and doubling the atomic weight of uranium, making it 240 (the modern figure is 238, so he wasn’t far off).
He was so confident in his system that he was sure the changes had to be correct.
Mendeleev also used his system to predict the weights and properties of ‘missing’, undiscovered elements which would fill the empty spaces in his table. There were elements under boron, aluminium and silicon which he knew must have similar properties. He called them eka- (the number 1 in Sanskrit) boron, eka-aluminium and eka-silicon.
When he first published his work in 1869, there wasn’t much interest, until he published a revised table two years later. He had revised the table, listing elements vertically rather than in horizontal rows. This work was then translated and received a great deal of interest from both Russian and foreign scientists.
In 1875, eka-aluminium was discovered and named gallium (after the ancient name for France). Scandium’s discovery in 1879 filled the eka-boron slot and eka-silicon was filled by germanium in 1886. Mendeleev’s predicted atomic weights and properties were largely accurate.
Dimitri Mendeleev
In honour of Mendeleev’s contribution, an artificial element was discovered at the University of California at Berkeley. It was produced one atom at a time, with a total of 17 atoms being produced in total. The scientists named it Mendelevium, and it was added to the periodic table as element 101.
Images: www.wikipedia.org, www.alchemywebsite.com, www.kullabs.com, www.chemwiki.ukdavis.edu, www.springer.com
Source: Morris, Richard, The Last Sorcerers—The Path From Alchemy to the Periodic Table, Joseph Henry Press, Washington D.C, Copyright, National Academy of Sciences.
