The Perfect Idea: Making Sense of Matter

Dmitri Mendeleev http://dmitri-mendeleev.org/Background.html

Dmitri Mendeleev
(Image: http://dmitri-mendeleev.org)

 

Dmitri Mendeleev was a Russian chemist, inventor and teacher.

He was, essentially, the father of the Periodic Table.

The birth of the Periodic Table, however, involved a long, lengthy process of discovery.

As is the nature of science, the Periodic Table was a process of building on, acquiring and organising knowledge.

Detail of a painting by Joseph Wright of Derby depicting the discovering of the element Phosphorus Retrieved from:  https://en.wikipedia.org/wiki/File:Henning_brand.jpg

Discovery of the element Phosphorus
(Image: https://en.wikipedia.org)

A brief history of the Periodic Table:

1649 - Hennig Brand was the first person in history to find a new element while trying to discover the Philosopher's Stone. He produced a glowing white substance, which he named phosphorus. This raised the question of what it meant for a substance to be an element.
1661 - Robert Boyle defined an element as "a substance that cannot be broken down into a simpler substance by a chemical reaction".
1789 - Antoine Laurent de Lavoisier wrote the first modern textbook about chemistry. It contained a list of "simple substances" that Lavoisier believed could not be broken down further, which included oxygen, nitrogen, hydrogen, phosphorus, mercury, zinc and sulfur, which formed the basis for the modern list of elements.
1817 - Johann Wolfgang Döbereiner began to formulate one of the earliest attempts to classify the elements. In 1829, he found that he could form some of the elements into groups of three, with the members of each group having related properties. He termed these groups triads.
1862 - Alexandre-Emile Béguyer de Chancourtois, a French geologist, was the first person to notice the periodicity of the elements — similar elements occurring at regular intervals when they are ordered by their atomic weights. He devised an early form of periodic table.
1864 - The English chemist John Newlands classified sixty-two of the known elements into seven groups, based on their physical properties. Newlands noted that many pairs of similar elements existed, which differed by some multiple of eight in mass number, and was the first to assign them an atomic number. He called it the 'law of octaves'.

Mendeleev claimed the Periodic Table came to him in a dream where the elements fell into place

The first impulse: rank the elements in order of their weight © Sciengist

The first impulse: rank the elements in order of their weight © Sciengist

The idea of the Periodic Table would have come to Mendeleev in the context of the thought about the elements.

It was like many other important scientific advances: its time was ripe and, in hindsight, it seems obvious.

By Mendeleev's time, over 60 elements had been identified (today over 110 are known.) In Mendeleev's day the atom was considered to be the most basic particle of matter (electrons, protons, and neutrons were discovered later). There was also growing information about the various properties of the different elements. For example John Dalton had calculated the first relative weights of atoms and compounds. These would provide the key means of organizing the elements into the periodic table.

Using this information, the first impulse would be to arrange the elements an a sequence of growing weight.

It now seems logic that the elements would be arranged according to their properties

The elements get heavier, but their properties recur 'Periodically' © Sciengist

The elements get heavier, but their properties recur 'Periodically' © Sciengist

 

However, it was as if Mendeleev were doing a jigsaw with one third of the pieces missing, and the other pieces broken!

He had written the properties of the elements on pieces of card and, tradition has it, that after organising the cards while playing patience, he suddenly realised that by arranging the element cards in order of increasing atomic weight, certain types of element regularly occurred.

He was the first to put elements into their correct places in the table. In some cases the relative atomic mass had been wrongly calculated by others.

By correcting the relative atomic mass he put the element in the correct place.

Although others had come so close, Mendeleev was credited with the discovery of the Periodic Table thanks to his foresight

The greatness of Mendeleev was that not only did he leave spaces for elements that were not yet discovered but he predicted properties of five of these elements and their compounds. These missing elements were discovered by others within his lifetime. They were gallium, scandium and, although two other elements whose properties were predicted were not discovered for 50 years.
The noble gases, not predicted by Mendleleev, were discovered in the 1890s and he was at first dismayed by this but later realised that were further proof of the Periodic Table. The element, atomic number 101, has been named after Mendeleev, a even rare distinction. This is surely deserved by the original formulator of the Periodic Table.

I look at my watch, 1 am; I look at my desk; it is wood; I look at my pen; it is steel.

It is all the same stuff: protons, neutrons and electrons!

I am amazed.

The first printed Periodic Table of the Elements

The first printed Periodic Table of the Elements

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