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Atomic Numbers

posted Jan 28, 2015, 2:21 AM by Ranmini Perera   [ updated Nov 30, 2015, 12:50 AM by Upali Salpadoru ]
What has a 1915 map of Galipoli to do with the numbering of atoms in chemistry? 

Be patient!


Throughout the development of chemistry , from Dalton’s Atomic Theory  to  Mendeleev Periodic Law in 1869,  i
dentifying atoms was by the relative weights of atoms; 

Atomic weights. When atoms were in the ascending order of their weights every element obtained a place number.

The chemists  knew they were significant some way. How or why;  they did not have a clue.

Fig.1 Map of Galipoli.  WW. 1.

 You cannot blame them.  J.J. Thomson discovered the electron  28 years later. He introduced the plum pudding model of the atom in 1904. Rutherford’s  postulation of the  mass aggregation in the core of an atom  came in 1911. Soon after, Niels Bohr worked out the electron orbits.

The numbers assigned,  helped the  chemists to correlate the Group numbers in the Periodic Table with the valency electrons. Rutherford obtained Hydrogen nuclei from Nitrogen atoms. This was the discovery of the Proton.(Hydrogen nucleus is really a Proton) .  But the variation of proton numbers remained a mystery. Only when  Henry Mosely, a pupil of Rutherford,  peeped into the nuclei of atoms, using X rays the mystery began to unravel.

Fig. 2. Henry Mosely 1887 - 1915.

It was after the 50th Anniversary of the Periodic table, Henry Mosely  peeped into atomic nuclei, using X’rays. The 26 year old guy wrote, “There is in the atom a fundamental quantity which increases by regular steps as we pass from each element to the next.  This quantity can only be the charge on the central positive nucleus.”

This is the Atomic Number, which is really the number of protons in the nucleus of an atom.

At the same time Frederick Soddy announced the presence of Isotopes "Some substances having different radioactive properties and different atomic weights could have identical chemical properties.

If all these substances were to be accommodated in separate cages in the Periodic Table,  it would have  been gigantic  one. So the Chemists and Physicists  decided to keep them in the same cage in the table and called them ‘isotopes’ meaning “same place”.Usually, the dawn of a new theory announces the death knell of a few  existing laws. But Mosley’s Law refined and illuminated many of the assumptions of the era, such as the Atomic model and Periodic law.

The only crucial change was the use of Atomic  Numbers , instead of mass numbers, in the sequence of elements in the Periodic Table.

Just as Mendeleev had done, Mosely was able to predict the existence of undiscovered elements. He showed the existence of gaps in the sequence of atomic numbers 43,61,72 and 75. He was even bold enough to predict the the Lanthanide series should have 15 elements exactly. Two of the predicted numbers were synthesized while the other two were discovered between 1923 and 24.

“It was a fiasco begun in February 1915. The flotilla retreated after sustaining heavy damage from Turkish guns. In April, a landing on the Gallipoli Penninsula  was planned. The Turks from the high ground poured  artillery and machine gun fire down on Australian, New Zealand, Irish, French and British troops below The British forces withdrew at the end of the year.
Casualties - approximately 252,000 for the British/French.” 

The French Revolutionary committee guillotined  Antoine Lavosier saying, “The Republic does not need Scientists”. 

Winston Churchill  sent the young genius, Henry Mosely as a foot soldier to receive a rifle bullet, for all what he had accomplished. 


Isaac Asimov had written,  "In view of what he [Moseley] might still have accomplished ... his death might well have been the most costly single death of the War to mankind generally."

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