This is the 100th post in my Chemistry365 project, an idea that started just over three months ago. I did not know what response I would get and never expected the number of visits to go over 10 000, so to be hitting 20 000 visits in the near future is just incredible. Thank you so much. This significant post will focus on the big ideas in chemistry that have lasted right through until today and I think will continue to have an influence into the future.
Atoms
The first idea comes from philosopher, Democritus in Ancient Greece who was the first to propose that all matter was made of small indivisible particles called atoms. The atoms are indestructible and have always been and always will be in motion. He also postulated that there was an infinite number and type of atoms differing in shape and size. This was in the year 465BC.
Together with Leucippus and Epicurus, Democritus, went on to develop ideas on the shapes of atoms and how they connected with one another based on the characteristics of substances. Iron for example had solid atoms with strong hooklike features locking them into place. Water atoms were surmised to be smooth and slippery. The atoms of salt were thought to be sharp and pointed because of their taste. The trio thought that the atoms of air were light and able to whirl and spread through all materials. There was no way for these theories to be proven although quantum mechanics tell us that atoms interact via electric and magnetic force fields. Bertrand Russell suggests in A History of Western Philosophy that it was a lucky hypothesis that has only been recently proven.
Molecules
The atomic theory proposed by Democritus, Leucippus and Epicurus was ignored for almost two millennia in favour of a theory involving four elements, air, water, fire and earth which led to the development of alchemy. It was not until the 17th century where the atomic theory was revived through the works of René Descartes, Pierre Gassendi and Isaac Newton.
Descartes and Gassendi reasoned that the size and shape of atoms moving resulted in the properties of matter. Heat was a product of small round atoms. Cold was due to atoms shaped like pyramids to explain the pricking sensation of severe cold. Solid matter were the result of atoms held together by interlacing hooks. Newton acknowledged these theories but he believed that the particles were attracted by some force which “in immediate contact is extremely strong, at small distances performs the chemical operations, and reaches not far from particles with any sensible effect.” in
Opticks in 1704.
It was Robert Boyle in 1661 in The Sceptical Chymist who first proposed the idea of aggregates of bonded atoms, that is, molecules. He also went further and said that only a chemical change causes the rearrangement of these aggregates.
The Periodic Table
Mendeleev's 1869 Periodic Table
Dmitri Mendeleev discovered the periodicity of the elements and compiled the first Periodic Table. He arranged the then known 63 elements into a Periodic Table based on atomic mass and published in Principles of Chemistry in 1869. Mendeleev also left space for elements that had not yet been discovered like eke-silicon and eke-boron but did not include any noble gases as they had not been discovered. The original time has been modified and corrected several times mostly by Henry Moseley before coming to today’s layout.
The Laws of Thermodynamics
An American physicist, chemist and mathematician, Josiah Willard Gibbs provided much of the theoretical foundation for classical thermodynamics and physical chemistry. Between 1876 and 1878, Gibbs wrote a series of papers on the graphical analysis of multi-phase systems, (systems consisting of gas, liquid and/or solids over a plot of temperatures and pressures). Theses series of papers were published as a 300 page volume titled, On the Equilibrium of Heterogeneous Substances.
This together with Hermann von Helmholtz’s paper, Thermodynamik chemischer Vorgänge began chemical thermodynamics and a large part of physical chemistry.
Equilibirium
A chemical system is in equilibrium when the quantities of chemical reactants and products do not and cannot change over time without an external influence at that particular temperature, pressure and composition. A chemical system in equilibrium can be considered to be a stable state. Any changes to the temperature, pressure and composition is a change in the external influence which would lead to a change in the chemical system.
The equation of chemical equilibrium can be expressed symbolically as:
reactant(s) 
product(s)
This is summarised in Le Chatelier’s principle, after the chemist, Henry Louis Le Chatelier who studied equilibrium reactions:
- If a chemical system at equilibrium experiences a change in concentration, temperature, volume, or partial pressure, then the equilibrium shifts to counteract the imposed change and a new equilibrium is established.
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These ideas are ones that I find myself returning to time after time when talking about science in different fields. Perhaps not explicitly but the principles that come from these ideas are applied in some way. I just find myself returning back to these fundamental concepts time and time again no matter what I do.
