Happy new year! New Year New Topic! Let us begin this new year by delving into a very basic topic in Chemistry – The Periodic Table.Understanding the Periodic table is at the heart of the study of Chemistry.In this post we shall start to explore how exactly this table was developed.Lets go back in time, where only a few elements were known to man and begin our journey into the world of elements.
Earlier it was believed that the universe was made up of four basic elements – Air,Water,Fire and Earth. Aristotle,the Greek philosopher, explained that when a log of wood was burned, one could see the air escaping from it due to fire and that the remaining ash was earth.This theory was widely accepted for many years.Democritus proposed that all matter is made up of atoms , which are the smallest ,indivisible part of matter.His theory was not accepted until after 2000 years of his death!People continued to believe Aristotle’s theory for ages.Modern Chemistry was born due to the work of many great chemists , who started discovering elements and thus expanding the knowledge of matter.Let us now talk about these amazing scientists and their discoveries, which lead to the formation of the modern periodic table.
1)Joseph Priestley (1733-1804)–
He was an English chemist,a multi-subject teacher and a person who loved to experiment with various things.He started experimenting with acids- studying the effect of acids of different substances.He observed that pouring acids onto substances, lead to evolution of different gases.He collected these gases and started studying their properties.This eventually lead to the discovery that air was composed of many gases!
Priestley focussed sunlight on mercury calx (red powder -oxide of mercury) and was amazed to see that it disintegrated to form liquid mercury.However, he also observed that some gas was given out during this process.This gas was collected and many experiments were conducted to study its properties.Finally, the gas which is fundamental to life on earth was discovered- OXYGEN!!
In a brewery, he collected the gas (CO2) formed during beer formation and dissolved it in water and thus made sparkling water! Thus, he is the inventor of carbonated water. Through all these discoveries, it was revealed that air is made up of a number of gases,each with different chemical and physical properties.Thus, Aristotle’s theory of 4 basic elements was proved to be incorrect and search for new elements started.
2)Antoine Lavoisier (1743-1794)–
He was a French Chemist,who discovered the law of conservation of mass, which in turn lead to the discovery of many new elements.Thus, he is rightly called as the ‘Father of modern Chemistry’.
In 1772,he along with other chemists,Antoine Lavoisier, bought a diamond and placed it in a closed glass jar.They focused sun’s rays on it using a giant magnifying glass.The result of this experiment was that the diamond burned and disappeared!! Although, when they measured the closed jar, its weight remained constant! They concluded that diamond had changed its form and was converted to some invisible gas which remained intact inside the closed jar.
He discovered that when sulphur was burned , it gained weight.He thus concluded that air was absorbed by sulphur, which lead to its increased mass.He took up Priestley’s idea of oxygen and through experiments found out that this gas was breathable and more combustible than normal air.Thus, he too made his contribution in the discovery of oxygen and its properties.
So, now it was understood that elements combined with oxygen and existed in a very different form in nature.After this revelation,many new elements like titanium,vanadium,beryllium, were discovered all over the world.So how many elements were there in the universe? Chemist started their research to find out the answer to this question and thus the search for new elements began.
3)Humphry Davy (1778-1829)–
Humphry Davy was a very talented, handsome,young English Chemist.At an tender age of 19, he started studying Chemistry and just in two years when his age was around 21, he was already proposing ideas and doing experiments that would surprise the most proficient chemists.
He was a native of Penzance, a remote town in England.At the age of 16, his father passed away and the responsibility to provide for his family fell on his shoulder.He started working in an apothecary.However, his interest in learning never waned. In the same year when his father died, Antoine Lavoisier published his finding in a scientific paper.Young Davy read it and he was mesmerized! He started experimenting right away and found out that heat was not an element, as proposed by Lavoisier, but a form of energy.He was then admitted to ‘Pneumatic Institution’ in Bristol.Here, he made and tested various gases ,which were found by Priestley and Lavoisier.He was so deeply committed to the study of the effects of these gases that he himself started inhaling them and noting down their effects on his body.He even tested some dangerous gases on himself which produced numbness,illness and sometimes laughter.Yes !With his assistant , he would heat crystals of ammonium nitrate.
(NH4NO3) → heated → N2O + 2 H2O
, collect the gas released in a green oiled-silk bag, pass it through water vapour to remove impurities and then inhale it through a mouthpiece. Humphrey Davy discovered Nitrous oxide (N2O) – THE LAUGHING GAS.
In 1800, the Italian scientist Alessandro Volta introduced the first battery made from Copper,zinc and cardboard dipped in salt water.The electric current produced by this battery ,when passed through water,split water into its components – namely hydrogen and oxygen. Davy read about this used this for what is now called electrolysis .Davy started using electricity as a powerful tool to discover new elements.He was able to isolate a series of substances for the first time through electrolysis- potassium(from caustic potash) and sodium(from caustic soda) in 1807 and calcium, strontium, barium and magnesium the following year.
By the 19th century , so many elements were discovered(around 63) but chemists could not classify them yet.These elements looked like some random entities which showed no common pattern.Thus, began attempts to classify these elements.
There were other attempts made to classify the elements in the 18th century too.
4)Johann Wolfgang Döbereiner(1780-1849)-
In 1817, a german scientist named Johann Wolfgang Döbereiner,sorted elements into Döbereiner’s triads.He studied elements in groups of three(triads) and found similarities in their properties.He used the atomic mass concept proposed by John Dalton and found out that the mass of the middle element of the triad is approximately the average of the first and third element’s atomic mass.
e.g.-
Element |
Atomic mass |
|
Chlorine |
35 |
|
Bromine |
80 |
|
Iodine |
127 |
Average of masses of Cl and I = (35+127)÷2 = 81 ≈ Mass of Bromine (80).
Element |
Atomic mass |
|
Carbon |
12 |
|
Nitrogen |
14 |
|
Oxygen |
16 |
Average of masses of C and O = (12+16)÷2 = 14 = Mass of Bromine (80).
However there were drawbacks of this theory.
Though this theory could be successfully applied to some elements, it could not be generalised to all known elements at that time.e.g. -Mn,Ni,Co,Zn and Cu have similar properties, but they cannot be placed into triads. Moreover, many groups of three adjacent elements were not chemically similar and thus could not be grouped.
5)John Newland (1837-1898)-
Along came another chemist, John Alexander Reina Newlands , who made another attempt at classifying elements.The exact atomic structure was not known at this time and thus all scientists were struggling to categorise elements and finding a pattern in their properties.He noticed that is he arranged the elements(known at that time) in groups of seven and then starting a new row with the eighth element, the first and the eighth elements had similar properties.He compared this behaviour of elements with octaves in music.
|
1) H |
8) F |
|
2) Li |
9) Na |
|
3) G |
10) Mg |
|
4) Bo |
11) Al |
|
5) C |
12) Si |
|
6) N |
13) P |
|
7) O |
14) S |
According to Newland, Li & Na ; B & Al ; C & Si ; N & P etc have similar properties. Though this correlation was valid for some elements it again could not be applied to all the elements. Thus, his table was rejected by the Journal of the Chemical Society.
Many attempts to classify elements continued , but none came close to the effort made by Dmitri Mendeleev! We shall talk about this great scientist and continue our journey to arrive at the modern periodic table, in our next post.Till then,
Be a perpetual student of life and keep learning !
Good Day !
References and further Reading –
1)http://www.hometrainingtools.com/a/four-elements
2)https://en.wikipedia.org/wiki/Joseph_Priestley
3)www.famousscientists.org/antoine-lavoiser
4)The mystery of matter – out of thin air documentary.
5)http://www.bbc.co.uk/history/historic_figures/davy_humphrey.shtml
6)https://publicdomainreview.org/2014/08/06/o-excellent-air-bag-humphry-davy-and-nitrous-oxide/
Image source –
1)https://en.wikipedia.org/wiki/Joseph_Priestley#/media/File:Priestley.jpg
2)By Louis Jean Desire Delaistre, after Boilly – Courtesy of Chemical Achievers, Public Domain, https://commons.wikimedia.org/w/index.php?curid=773055
3)http://www.historytoday.com/richard-cavendish/davy’s-lamp-described
4)By Carl August Schwerdgeburth, 1785-1878 (engraver), and Fritz Ries, 1826-1857 (painter) – http://www.sil.si.edu/digitalcollections/hst/scientific-identity/explore.htm (reworked), Public Domain, https://commons.wikimedia.org/w/index.php?curid=140806
5)By The original uploader was DALIBRI at German Wikipedia – Transferred from de.wikipedia to Commons., Public Domain, https://commons.wikimedia.org/w/index.php?curid=2284792
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