Isotopes
Year of Discovery: 1913
What Is It? Isotopes are different forms of the same chemical element that
have identical physical and chemical properties but different atomic
weights.
Who Discovered It? Frederick Soddy
Why Is This One of the 100 Greatest?
Isotopes of an element are slightly different forms of that element. Isotopes have the
same chemical, physical, and electrical properties as the original element, but have a different number of neutrons in their nucleus. The discovery of isotopes created a new dimension
and concept for physics and chemistry.
This discovery answered baffling problems that had stymied physics researchers
studying radioactive elements. The study of isotopes became a key foundation for the development of atomic power and weapons. Isotopes are also critical to geology since carbon
dating and other rock-dating techniques all depend on the ratios of specific isotopes.
This one discovery removed roadblocks to scientific progress, opened new fields of
physics and chemistry research, and provided essential research tools to earth science research.
How Was It Discovered?
Frederick Soddy was born in 1877 in Sussex, England. In 1910 Soddy accepted a position at the University of Glasgow as a lecturer in radioactivity and chemistry.
The study of radioactive elements was still exciting and new. Radioactive elements
were identified by differences in their mass, atomic charge, and radioactive properties, including the kinds and energies of different particles they emitted.
However, using this system, scientists had already identified 40 to 50 radioactive elements. But there existed only 10 to 12 places for all of these radioactive elements on the periodic chart of elements. Either Mendeleyev’s periodic chart was wrong or—for some
unknown reason—radioactive elements fell outside the logic and order of the periodic chart.
Neither answer made any sense, and radioactive research ground to a halt.
Soddy decided to study the three known subatomic particles emitted by the various radioactive elements (alpha, beta, and gamma particles). Soddy found that alpha particle held
a positive charge of two (as would two protons) and a mass equal to four protons. Gamma
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