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Periodic Table-history.

posted Jan 28, 2015, 8:41 PM by Ranmini Perera   [ updated Nov 4, 2016, 8:33 PM by Upali Salpadoru ]






Fig.1. 1834 - 1907   Dimitry Mendeleev..








It isn’t right to say anything is impossible in science, but I doubt anybody counting all the chemicals in the world.  When it comes to elements , the ancients had only 4 or 5.  
Earth, Water, Air, Fire and Aether. The present count is only 118 of which a few, at the tail end were man made.

The first element recognized by ‘Homo sapiens’, was probably gold; Hunters hurled gold nuggets at fleeing antelopes.  The metals, Ag, Fe, Pb, Cu, Hg and Sn, and the non metals sulphur and carbon, were commonly used by the ancient civilizations without labeling them as ‘elements’. Their elements were those 4 or 5 things named earlier.  

Ancient alchemists, in their pursuit of gold initiated the handling of chemicals.  In 1649 Henning Brand boiled human urine for a few days to find gold, and obtained Phosphorus instead. By the dawn of the 18th Century alchemy had given way to chemistry.   

He found similarities in groups of three elements which he named as triads.

He showed that the physical and chemical properties of the middle term is halfway of the other two. Chemists soon discovered more triads and they were even able to extend into longer groups. 

                                                   Fig. 2.  1817-1829, Johann Dobereiner

Triad 1

Property

Chlorine Cl

Bromine   Br

Iodine   I

State

Gas

Liquid

Solid

Colour

Greenish yellow Brown Very dark (purple vapour}

 Mass no.

35

80

127

 

 Triad 2.

Property

Lithium Li

Sodium Na

Potassium  K

Atomic weight

7

23 

39

Reaction with water

Reacts with water to form an alkali

Reacts violently with water forming an alkali

Reacts with water igniting the hydrogen released.

 

   In 1862  he used atomic weights to group the elements and recognize some sort of a regularity. He arranged the elements in the form of a spiral around a cylinder divided into 16 parts


 Fog. 3. A.E.Beguyer de Chancourtois

 

Fig. 4 John Newlands

 In 1863, he  introduced  the Law of Octaves. According to this law , elements arranged according to their atomic weights, every 8th element shows some sort of similarity, He compared this  to the Octaves in music toward the utter consternation of the diehard chemists .


 

 

Fig. 5 Lothar Meyer.

Just a few years later, Two students of Robert Boyle,  Lothar Meyer and Dimitry Mendeleef  discovered the periodicity of elements. Lothar Meyer plotted the volume of a gram molar of matter against their atomic weights.  He was able to group 28 elements,  into families and each family    showed a particular combining power which was termed as valency. Salt producing group (Alkali metals) and acid producing group (halogens) had the valency 1 while valency of the Calcium, Magnesium group was 2.



Fig. 6.  Lothar Meyer's  Atomic volume graph showing periodicity.

Although they independently discovered the same thing  at the same time  Lothar Meyer being a true gentleman acceded to the superiority of Mendeleef  . His reason being that only Mendeleev was able to predict in a convincing manner all about the undiscovered elements.

 

Mendeleev wrote  “The properties of elements are a periodic function of their Atomic Weights.” in 1869.

 He had so much of confidence in his theory,  he took two bold steps which a scientist wouldn’t normally  dare. First he changed the atomic weights of certain elements, stating they have not been determined correctly.  Then he reserved spaces in his arrangement forecasting the discovery of a few elements. He even gave the properties of the un-discovered elements.      

Using periodicity, he predicted characteristics of elements that had not yet been discovered. There were gaps in his periodic table, and he was certain that these gaps would be filled with elements with specific characteristics.

“He used the Sanskrit prefixes for one, two and three of the elements- eka, dvi and tri, depending on how many places the undiscovered element stood from known members of his table.” Courtsey: :Life 123

i.     Predicted  Eka-silicon  was named as  Germanium.

ii.    Predicted  Dvi- magnesium was named as Rhenium

Fig. 7. From Dobereiner to Mendeleev

Red = electro positivity     Blue = Electro negativity.

Fig.8. The  elements of the first 3 periods of  Periodic Table.

 In this section of the Periodic Table, ( Atomic numbers 1 to 18 )  it is possible to observe some of the magical features.  Mendeleev , in 1869,  without an idea of the internal structure of the atom,  (even the plum pudding model was proposed in 1904)  simply using only the properties of elements figured out the most amazing structure which has become an encyclopedia for the study of matter.


   In science, a Theory or a Law,  generally corrodes with time.   The Periodic Table has got highly polished and glitters in the light of modern technology.

In  Fig 2. The columns  are the groups  according to the number of electrons in the outer shell (shown by dots.  The horizontal rows are periods according to the number of orbits shown in black circles. The atomic number given for each element is equal to the number of positive charges, protons. In the nucleus.

All the properties of each element can be explained according to the electrical charges inside the atoms.  Those shaded in red have less than 4 e –  in their outer shells.  They  can shed  e – to  get the structure of an inert gas.

Taking examples from group 1  and 2 we get:-

    1. H  -   e  = H e +     ( Similar to Helium)
    2. Na - e     =  Na +     (Similar to Neon)
    3. Mg - 2 e      =   Mg ++   (similar to Neon)

                  

The atoms that donate e –    to form ions are  metals.  Shaded red.  Darker the colour easier to give e .. This tendency is described as electropositive.

Those that have an affinity to get e –    are in blue.   They are electronegative.

Example:-

    • Br  +  e –      = Br   ( similar to Argon)

Atoms wish to acquire  a  complete outer shell either by accepting or donating electrons.

The periodic table depicts a beautiful gradation of properties.  As you move to the right the affinity for electrons increase. This is due to the increasing number of protons.  Just as the electron number increases the volume of the atom increases due to repulsion.   Group 7 and 8  become gaseous.

As you come down the groups it become easy for them to donate electrons as extra shells are added.

Changing the size along Periods and Groups

 Fig. 9   Atomic volume.

Fig. 10  Some important trends.

Fig11 The modern version.


Glenn Seaborg 1912-1999

The current form of the Periodic Table was designed by Glenn Seaborg. To add the lanthanide and actinides below the table was his idea. He was responsible for the discovery of  elements  having  Atomic numbers 94 to 102. and over 100 isotopes, among the transuranium metals, He won the Nobel Prize for chemistry in 1951.




 The Song.
 
Refer U- tube for the tune.

Lyrics

There’s Hydrogen and Helium Then Lithium, Beryllium Boron, 

Carbon everywhere Nitrogen all through the air

With Oxygen so you can breathe And Fluorine for your pretty teeth

 Neon to light up the signs Sodium for salty times

Magnesium, Aluminium, Silicon Phosphorus, 

then Sulfur, Chlorine and Argon Potassium, and Calcium 

so you’ll grow strong 

Scandium, Titanium, Vanadium and Chromium and Manganese

CHORUS 

This is the Periodic Table 

Noble gas is stable Halogens and Alkali react agressively 

Each period will see new outer shells 

While electrons are added moving to the right

Iron is the 26th Then Cobalt, Nickel coins you get 

Copper, Zinc and Gallium Germanium and Arsenic

Selenium and Bromine film While Krypton helps light up your room 

Rubidium and Strontium then Yttrium, Zirconium

Niobium, Molybdenum, Technetium Ruthenium, Rhodium,

 Palladium Silver-ware then Cadmium and Indium 

Tin-cans, Antimony then Tellurium and Iodine and Xenon 

and then Caesium and…Barium is 56

and this is where the table splits 

Where Lanthanides have just begun 

Lanthanum, Cerium and Praseodymium

Neodymium’s next too Promethium, then 62’s Samarium, 

Europium, Gadolinium and Terbium Dysprosium, Holmium, 

Erbium, Thulium Ytterbium, Lutetium

Hafnium, Tantalum, Tungsten 

then we’re on to Rhenium, Osmium and Iridium Platinum, 

Gold to make you rich till you grow old 

Mercury to tell you when it’s really cold

Thallium and Lead then Bismuth for your tummy 

Polonium, Astatine would not be yummy 

Radon, Francium will last a little time 

Radium then Actinides at 89

REPEAT CHORUS

Actinium, Thorium, Protactinium Uranium, Neptunium, Plutonium Americium, Curium, Berkelium Californium, Einsteinium, Fermium Mendelevium, Nobelium, Lawrencium Rutherfordium, Dubnium, Seaborgium Bohrium, Hassium 

then Meitnerium Darmstadtium, Roentgenium, Copernicium

Ununtrium, Flerovium Ununpentium, Livermorium Ununseptium,

 Ununoctium And then we’re done!!


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