The Right Chemistry: Ernest Rutherford, a physicist honoured for chemistry

48

[ad_1]

Rutherford identified radioactivity as the spontaneous disintegration of unstable atoms with the emission of energy and smaller particles.

Article content

“All science is either physics or stamp collecting.” That quote, repeated in many articles and books, is attributed to Ernest Rutherford, widely recognized as the father of nuclear physics. However, there is little evidence he ever said it. The first reference can be traced back to a book by physicist John Bernal, written in 1939, two years after Rutherford’s death, in which the author makes a casual comment that “Rutherford used to divide science into physics and stamp collecting.”

Advertisement 2

Article content

There is also the question of what Rutherford meant if he did indeed utter such an opinion. The quote is often interpreted as denigrating other sciences and suggesting that physics is the only legitimate pursuit. Given that his own Nobel Prize, awarded in 1908, was in chemistry, and that his main collaborator at McGill University in the radioactivity experiments for which he received the prize was Frederick Soddy, a chemist, it is unlikely that Rutherford would have demeaned other sciences.

However, Rutherford is known to have been highly critical of theoreticians, such as Werner Heisenberg, disdaining theories he believed did not come from experiments, so it is possible that such words would have been a dig at theoreticians. Rutherford was above all an experimental physicist and he could have used the term “physics” to mean experimentation.

Advertisement 3

Article content

The New Zealand-born Rutherford was perhaps the greatest experimentalist since Michael Faraday. He identified radioactivity as the spontaneous disintegration of unstable atoms with the emission of energy and smaller particles. Those smaller particles were identified as electrons and helium nuclei which he named “beta” and “alpha” radiation respectively. Disintegration could also be accompanied by energetic electromagnetic waves he called “gamma rays.” Rutherford’s determination of “half-lives,” the time taken for half the atoms in a sample of a radioactive element to decay, laid the basis for radiocarbon dating. All this was the work carried out at McGill, for which he received the Nobel Prize, but Rutherford’s most famous discovery came after he left McGill to take up a post at the University of Manchester.

Advertisement 4

Article content

It was here that, in collaboration with Hans Geiger and Ernest Marsden, Rutherford carried out the “gold foil experiment” that would establish the structure of the atom as we know it. As early as the 5th century BC, Greek philosophers Leucippus and Democritus had introduced the idea that all matter is composed of uniform, solid, hard, incompressible and indestructible “atomos,” from the Greek for “indivisible.” Unfortunately, Aristotle, the most influential Greek philosopher, did not believe in atoms and so the concept lay dormant until the atomic theory was resuscitated by John Dalton in the early years of the 19th century. One hundred years later, J.J. Thomson, under whom Rutherford had studied, discovered the electron and formulated the “plum pudding model,” which described atoms as uniform spheres of positively charged matter in which electrons were embedded like plums in a pudding.

Advertisement 5

Article content

Then along came Rutherford’s classic experiment, which is described in every introductory chemistry and physics text. A thin piece of gold foil was exposed to a barrage of alpha particles emitted by the radioactive decay of radon, a gas that Rutherford had previously identified as a new element. A phosphorescent screen behind the gold foil flashed wherever it was struck by an alpha particle. Most of the alpha particles passed right through the gold foil, but some bounced back! An astounded Rutherford compared this to having a bullet fired at a piece of tissue paper rebounding. This could only happen, he deduced, if the Thomson model was wrong and gold atoms were mostly empty space, except for a tiny, dense, positively charged mass that repelled the positively charged alpha particles. That mass came to be called the “nucleus,” and was surrounded by empty space through which electrons circulated. Rutherford’s theory of atomic structure was essentially correct, although further refinements have shown that electrons do not circulate randomly about the nucleus, but rather are restricted to certain energy levels.

Advertisement 6

Article content

In 1971, New Zealand issued two stamps to commemorate the 100th anniversary of Rutherford’s birth. One of these accurately depicts the gold foil experiment, but the other shows a reaction in which nitrogen combines with an alpha particle to form an atom of oxygen and one of hydrogen. This is an illustration of the first-ever transmutation of an element with nitrogen being converted into oxygen that earned Rutherford a reputation as the “first successful alchemist.” Unfortunately, that reaction should not have appeared on the stamp for the simple reason that Rutherford never carried it out!

Rutherford did target nitrogen atoms with energetic alpha particles and showed that a proton, which is a simple hydrogen nucleus, was emitted, he did not identify the other products of the reaction. Actually, he believed the bombardment had caused the nitrogen atoms to break apart into other atoms he was unable to identify. It was Patrick Blackett, working in Rutherford’s lab at Cambridge, who studied this reaction extensively and in 1925 interpreted it correctly. The alpha particles had not caused the nitrogen nucleus to break apart, but rather had combined with it to form an atom of oxygen. Key to this work was Blackett’s development of the Wilson cloud chamber, a device that tracks the path of charged particles, for which he was awarded the 1948 Nobel Prize in physics. It was investigative journalist Steven B. Krivit who first brought this issue to light in 2017 and has made great efforts to correct the recorded history.

Advertisement 7

Article content

Rutherford has received many richly deserved accolades for his elucidation of radioactivity and formulation of the nuclear theory of the atom. But calling him “the world’s first successful alchemist,” as many publications have done is not correct, and Rutherford would surely have opposed the design of the stamp that shows him transforming nitrogen into oxygen. While he did not carry out this transformation, he did comment on another one. In his acceptance speech for the Nobel Prize in Chemistry, Rutherford quipped that “I have observed many transformations while working with radioactive materials, but none as rapid as my own from physicist to chemist.”

[email protected] 

Joe Schwarcz is director of McGill University’s Office for Science & Society (mcgill.ca/oss). He hosts The Dr. Joe Show on CJAD Radio 800 AM every Sunday from 3 to 4 p.m. 

Note: This column has been updated to acknowledge the work of Steven B. Krivit.

Advertisement 1

Comments

Postmedia is committed to maintaining a lively but civil forum for discussion and encourage all readers to share their views on our articles. Comments may take up to an hour for moderation before appearing on the site. We ask you to keep your comments relevant and respectful. We have enabled email notifications—you will now receive an email if you receive a reply to your comment, there is an update to a comment thread you follow or if a user you follow comments. Visit our Community Guidelines for more information and details on how to adjust your email settings.

[ad_2]

Source link

Leave a comment