TODAY IN SCIENCE HISTORY ®  •  TODAYINSCI ®
Celebrating 24 Years on the Web
Find science on or your birthday

107

Stories About Chemistry

INDEX

25. Fourteen Twins

They are called lanthanides. Such is their name because all of them - fourteen in all - are �lanthanum-like,� that is, resemble lanthanum and one another almost like so many drops of water. Because of this astonishing chemical similarity they are all situated in a single box, the box of lanthanum whose number in the table is 57.

Isn�t this some terrible misunderstanding?

Mendeleyev himself and many other scientists reasoned that each element had a single quite definite place in the Periodic Table.

But here fourteen inhabitants of the system have crowded into the same box, all of them elements of the third group and of the sixth period.

Why not try sorting them out among the other groups?

Many chemists have tried, among them Mendeleyev. They placed cerium in the fourth group, praseodymium in the fifth, neodymium in the sixth, and so on. But this distribution defied all logic. The main and secondary subgroups of the Mendeleyev Table contain similar elements. But cerium had very little in common with zirconium, praseodymium and neodymium were strangers to niobium and molybdenum. Nor could the other rare-earth elements (such is the general name for lanthanum and the lanthanides) find relatives in the corresponding groups. On the other hand, they resembled each other like twin brothers.

When chemists were asked what boxes of the table to place the lanthanides in, they shrugged their shoulders in bewilderment. Indeed, what could they say when they did not know the reason for the astonishing similarity of the lanthanides?

When chemists were asked what boxes of the table to place the lanthanides in, they shrugged their shoulders in bewilderment. Indeed, what could they say when they did not know the reason for the astonishing similarity of the lanthanides?

But the explanation proved quite simple.

The Periodic System has curious groups of elements whose atoms have quite a peculiar constitution. The last electron added to form these atoms does not settle in their outermost, or even in their second-last shells, but penetrates, in conformance with strict physical laws, right through to the third-last shell.

They feel quite cosy there and have no inclination to abandon their places under any circumstances. They participate in chemical reactions only in very rare cases.

Now since all the lanthanides have three electrons in their outer shells, they are trivalent, as a rule.

Nor is it accidental that the number of lanthanides is fourteen, neither more nor less. This is because there are exactly fourteen vacancies in the third-last shell of their atoms, the one that is being filled.

That is why chemists found it possible to place all the lanthanides in one single box together with lanthanum.


< back     next >

Thank you for sharing.
- 100 -
Sophie Germain
Gertrude Elion
Ernest Rutherford
James Chadwick
Marcel Proust
William Harvey
Johann Goethe
John Keynes
Carl Gauss
Paul Feyerabend
- 90 -
Antoine Lavoisier
Lise Meitner
Charles Babbage
Ibn Khaldun
Euclid
Ralph Emerson
Robert Bunsen
Frederick Banting
Andre Ampere
Winston Churchill
- 80 -
John Locke
Bronislaw Malinowski
Bible
Thomas Huxley
Alessandro Volta
Erwin Schrodinger
Wilhelm Roentgen
Louis Pasteur
Bertrand Russell
Jean Lamarck
- 70 -
Samuel Morse
John Wheeler
Nicolaus Copernicus
Robert Fulton
Pierre Laplace
Humphry Davy
Thomas Edison
Lord Kelvin
Theodore Roosevelt
Carolus Linnaeus
- 60 -
Francis Galton
Linus Pauling
Immanuel Kant
Martin Fischer
Robert Boyle
Karl Popper
Paul Dirac
Avicenna
James Watson
William Shakespeare
- 50 -
Stephen Hawking
Niels Bohr
Nikola Tesla
Rachel Carson
Max Planck
Henry Adams
Richard Dawkins
Werner Heisenberg
Alfred Wegener
John Dalton
- 40 -
Pierre Fermat
Edward Wilson
Johannes Kepler
Gustave Eiffel
Giordano Bruno
JJ Thomson
Thomas Kuhn
Leonardo DaVinci
Archimedes
David Hume
- 30 -
Andreas Vesalius
Rudolf Virchow
Richard Feynman
James Hutton
Alexander Fleming
Emile Durkheim
Benjamin Franklin
Robert Oppenheimer
Robert Hooke
Charles Kettering
- 20 -
Carl Sagan
James Maxwell
Marie Curie
Rene Descartes
Francis Crick
Hippocrates
Michael Faraday
Srinivasa Ramanujan
Francis Bacon
Galileo Galilei
- 10 -
Aristotle
John Watson
Rosalind Franklin
Michio Kaku
Isaac Asimov
Charles Darwin
Sigmund Freud
Albert Einstein
Florence Nightingale
Isaac Newton


by Ian Ellis
who invites your feedback
Thank you for sharing.
Today in Science History
Sign up for Newsletter
with quiz, quotes and more.