Friday, May 7, 2010

Divisible Part 1

Prologue                                             

The question regarding the very nature of the matter comprising the universe is one which has challenged human thought for millennia. From the time of the earliest Greek philosophers to modern day particles physicists, mankind has sought to understand the underlying structure of nature.

The majority of science prior to the 19th century was concerned with the behaviour of the macroscopic world we live in and predicting events. It was chemists who first tackled this difficult question. From their observations it would appear that elements we have may not be as fundamental as once believed. 

Atomos

The concept of matter being comprised of small indivisible units has been around for millennia. The first account of this in western history arose from the writings of the Greek philosopher Democritus (c.350 BC). In his writings he asserted that matter is made up of small indivisible particles which he referred to as “atomos”. This was one of the first examples of the idea that matter was not continuous. However this idea did not receive widespread support and was disputed by most influential philosophers at the time, Plato and Aristotle. The Greeks were philosophers, not experimentalists, so without any evidence this idea of atoms fell by the wayside.

Democritus


This idea of matter being comprised of small indivisible units would remain dormant until the late 18th century when a chemist, Antoine Lavoisier (1734-1794), pioneered the theory of reaction stoichiometry. This theory relies on the conservation of mass during chemical reactions. This conservation hinted that there may be some underlining relationship between the different elements. This theory was furthered by John Dalton (1766-1844) in 1804 to develop the concept of atomic weight. From this concept the theory of atoms was revived. Dalton stated that all elements are made of small particles called atoms and that all atoms of a given element are identical. Noted French chemist Gay-Lussac (1774-1850) also arrived at a similar conclusion based on his theory of how substances react in discrete amounts. However all was not right with these theories. There was the snag that as measurements became more accurate the mass of elements was not consistent (this would not be solved until the idea of isotopes was theorized).

In the 18th and 19th centuries there was a great flourish of discoveries of new, exciting elements. The question of whether these elements related to one another in any way arose. At this time a Russian chemist, Dmitri Mendeleev (1834-1907), began trying to answer this question. He attempted to list out all of the known elements and classify them into groups according to their chemical properties. It was only when he began to group them by their atomic weight and similar chemical properties a pattern began to emerge. Noting several gaps in his new table, he predicted new elements which would have certain chemical properties. This became the familiar table known as the Periodic Table of Elements (1869). For the first time there was a hint that the elements may not be fundamental as had been believed. His work was vindicated when he predicted two new elements which were found in 1876 (Gallium) and in 1886 (Germanium). 

Mendeleev's Periodic Table

1 comments:

Abed said...

Very useful post. Thanks for sharing your information

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