Discoverer In Detail: Ernest Rutherford
The development of atomic theory throughout the decades has played a significant role in the chemistry
that we know today. Firstly because the building blocks of matter are atoms, determining the structure has led to the understanding bonding through different elements as well as helped create new elements through experiments.
Rutherford’s knowledge regarding atomic theory was primarily based on the works of JJ Thompson. From Thompson’s discovery that there
were two parts of atom held together by electrostatic attraction[i]. A heavier part, responsible for the majority of mass of the atom and a negatively charged electron. And also ‘‘plum pudding’’ model of an atom. Rutherford had substantial knowledge on areas such a
radioactivity.[ii]
Prior to his revolutionary atomic model discovery, Rutherford was working on radioactivity. Rutherford at the time had successfully marked out
a wholly new branch of physics. He discovered a detector for electromagnetic waves. He and Professor Thomson were working together, studying the behavior of ions in gases, the mobility of ions with respect to the force of the electric field, and on related topics like the photoelectric effect.[iii] While experimenting on radioactivity during 1899, he discovered two distinctive types of radiation emitted by thorium and uranium which he named alpha and beta. These rays were distinguished on the basis of penetrating power. This was the fore front to the beginning of his Alpha particle scattering experiment.[iv] At Manchester, Ernest along with the support of H. Geiger
developed a method for detecting a single alpha particle and counting the number emitted from radium. This sparked the Experiment.
The basic setup of the experiment were alpha particles being shot from a radioactive source focused into a narrow beam passing through
a slit in a lead screen. This was directed to a gold foil. The foil was then surrounded by a wall of zinc sulphide which would make it fluorescent.
This meant that when alpha particles struck the wall it would exhibit scintillations (tiny flashes). Patterns formed by the scintillations would
provide information as to how the charges were distributed inside the atom.[v]
.
With the J.J Thomas’s ‘plum pudding’ model in mind, Rutherford expected very minimal alpha particle deflections as they were bombarded on the foil. Rutherford reasoned that if the positively charged material in each gold atom is spread out over the entire volume of the atom, as J.J Thomas had proposed, its electric field would not be intense enough to repel the tiny, very fast moving, positively charged α particle to any significant degree.[vi] Instead they would pass straight through the larger gold atoms. The scintillations were only supposed to be observed right behind the foil, exactly opposite to the source of alpha particles. However the majority of the flashes were observed behind the foil, a few were also seen near the source. According to Rutherford, it was like ‘‘firing a cannonball on a tissue paper and seeing it bounce against the paper right back at him on certain occasions’’'[vii]. Since alpha particles were positively charged, the only logical explanation therefore was that the positive charged atoms was not as dispersed as in the Pudding Model. Instead, Rutherford guessed that they should be concentrated in a very small volume in the center. This specific portion of Rutherford’s model still holds even up to this day.[viii]
As a result in was time to modify J.J Thomas model of the atom. If Thomson's model is correct then there would be little to nothing to deflect the alpha particle back because all the mass is spread out. Rutherford Concluded that only a positively charged and relatively heavy target particle, such as the proposed nucleus, could account for such strong repulsion. The negative electrons that balanced electrically to the positive nuclear charge were regarded as traveling in circular orbits about the nucleus. The electrostatic force of attraction between electrons and nucleus was related to the gravitational force of attraction between the revolving planets and the Sun. Most of this planetary atom was open space and offered no resistance to the passage of the alpha particles. [ix]
Apart from Rutherford’s work with the atomic structure h has enabled further progress in chemistry and in science. Scientist Neils Bohr developed on what Rutherford atom structure. Bohr saw that the flaw in Rutherford's model is that it contains charges that are accelerating. The charges are on the electrons and the acceleration is due to the electrons always changing direction as they move around their orbits. He realised that electrons inside atoms can't radiate energy continuously.[x] Therefore, Bohr established his own atomic model which was more accurate, derived from Rutherford’s model.
Rutherford has also been acknowledging as the man who paved the way for spitting an atom. Also known as nuclear fission. He bombarded radioactive uranium with neutrons to split the uranium nucleus in half and release huge amounts of energy.[xi] As the nucleus is halved, it emitted extra neutrons which spin off and split more uranium nuclei, creating still more energy and setting off a chain reaction.[xii] James Chadwick who was working under Rutherford at the time did further research into Rutherford’s discovery which led to nuclear plants
producing nuclear energy, and the atomic bomb. He adapted a device he had developed back in New Zealand, using it to detect electro-magnetic waves, and in 1896 succeeded in detecting waves over several hundred meters. This was used to detect Submarines in World War 2.[xiii]
Rutherford also became interested in radioactivity after radioactive atoms were discovered in 1896. He discovered that radioactive atoms gave off two different types of rays alpha and beta. From this he discovered radon, a radioactive gas. From this Rutherford developed a method for working out the age of material such as rocks by measuring the amount of radioactive decay that has taken place, that is, the amount of radioactive material being tested. [xiv]
Rutherford's work has led to some important practical applications in the 21st century including big advances in the field of medicine. Understanding the nucleus and radioactivity has led to many diagnostic techniques for medicine like positron emission tomography, or the radiotherapy cancer treatments that people receive.[xv]
[i] Encyclopedia Britannica. 2013. Thomson atomic model. [online] Available at:
http://www.britannica.com/EBchecked/topic/593128/Thomson-atomic-model
[Accessed: 10 Mar 2014].
[ii] CARL VILLANUEVA, J. 2009. Plum Pudding Model. [online] Available at:
http://www.universetoday.com/38326/plum-pudding-model/ [Accessed: 10 Mar
2014].
[iii] Chalmers, A. 2014. The Rutherford
Journal - The New Zealand Journal for the History and Philosophy of Science and
Technology. [online] Available at:
http://www.rutherfordjournal.org/article010101.html [Accessed: 11 Mar
2014].
[iv]
Aip.org.
2014. Rutherford's Nuclear World: The Story of the Discovery of the Nucleus | Sections | American institute of Physics. [online] Available at:
http://www.aip.org/history/exhibits/rutherford/sections/alpha-particles-atom.html
[Accessed: 10 Mar 2014].
[v]
Sharwood,
J. and Corrigan, D. 2007. Nelson chemistry. South Melbourne: Thomson
Learning.
[vi] Media, N. 2014. Ernest Rutherford - Biographical. [online] Available at: http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-bio.html [Accessed: 10 Mar 2014].
[vii]
NZEDGE.COM. 2014. Ernest Rutherford. [online] Available at:
http://www.nzedge.com/ernest-rutherford/ [Accessed: 10 Mar
2014].
[viii]
P.Kilman14. [online] Available at:
http://undsci.berkeley.edu/lessons/pdfs/rutherford.pdf [Accessed: 10 Mar
2014].
[ix]
Sharwood, J. and Corrigan, D. 2007. Nelson chemistry. South Melbourne: Thomson
Learning.
[x]
Siegfried, T. 2013. When the atom went quantum: Bohr's revolutionary atomic theory turns
100. Science News, 184
(1), pp. 20--24.
[xi]
Chalmers, A. 2014. The Rutherford
Journal - The New Zealand Journal for the History and Philosophy of Science and
Technology. [online] Available at:
http://www.rutherfordjournal.org/article010101.html [Accessed: 11 Mar
2014].
[xii]
Vigyanprasar.gov.in. 2014. Ernest Rutherford. [online] Available at:
http://www.vigyanprasar.gov.in/scientists/ERutherford.htm [Accessed: 10 Mar
2014].
[xiii]
Media,
N. 2014. Ernest Rutherford - Biographical. [online] Available at:
http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-bio.html
[Accessed: 10 Mar 2014].
[xiv]
Christchurchcitylibraries.com. 2014. Ernest Rutherford - Kids - Christchurch City Libraries. [online] Available at:
http://christchurchcitylibraries.com/kids/famousnewzealanders/ernest.asp
[Accessed: 12 Mar 2014].
[xv]
Chemheritage.org. 2014. Ernest Rutherford | Chemical Heritage Foundation. [online]
Available at:
http://www.chemheritage.org/discover/online-resources/chemistry-in-history/themes/atomic-and-nuclear-structure/rutherford.aspx
[Accessed: 10 Mar 2014].
that we know today. Firstly because the building blocks of matter are atoms, determining the structure has led to the understanding bonding through different elements as well as helped create new elements through experiments.
Rutherford’s knowledge regarding atomic theory was primarily based on the works of JJ Thompson. From Thompson’s discovery that there
were two parts of atom held together by electrostatic attraction[i]. A heavier part, responsible for the majority of mass of the atom and a negatively charged electron. And also ‘‘plum pudding’’ model of an atom. Rutherford had substantial knowledge on areas such a
radioactivity.[ii]
Prior to his revolutionary atomic model discovery, Rutherford was working on radioactivity. Rutherford at the time had successfully marked out
a wholly new branch of physics. He discovered a detector for electromagnetic waves. He and Professor Thomson were working together, studying the behavior of ions in gases, the mobility of ions with respect to the force of the electric field, and on related topics like the photoelectric effect.[iii] While experimenting on radioactivity during 1899, he discovered two distinctive types of radiation emitted by thorium and uranium which he named alpha and beta. These rays were distinguished on the basis of penetrating power. This was the fore front to the beginning of his Alpha particle scattering experiment.[iv] At Manchester, Ernest along with the support of H. Geiger
developed a method for detecting a single alpha particle and counting the number emitted from radium. This sparked the Experiment.
The basic setup of the experiment were alpha particles being shot from a radioactive source focused into a narrow beam passing through
a slit in a lead screen. This was directed to a gold foil. The foil was then surrounded by a wall of zinc sulphide which would make it fluorescent.
This meant that when alpha particles struck the wall it would exhibit scintillations (tiny flashes). Patterns formed by the scintillations would
provide information as to how the charges were distributed inside the atom.[v]
.
With the J.J Thomas’s ‘plum pudding’ model in mind, Rutherford expected very minimal alpha particle deflections as they were bombarded on the foil. Rutherford reasoned that if the positively charged material in each gold atom is spread out over the entire volume of the atom, as J.J Thomas had proposed, its electric field would not be intense enough to repel the tiny, very fast moving, positively charged α particle to any significant degree.[vi] Instead they would pass straight through the larger gold atoms. The scintillations were only supposed to be observed right behind the foil, exactly opposite to the source of alpha particles. However the majority of the flashes were observed behind the foil, a few were also seen near the source. According to Rutherford, it was like ‘‘firing a cannonball on a tissue paper and seeing it bounce against the paper right back at him on certain occasions’’'[vii]. Since alpha particles were positively charged, the only logical explanation therefore was that the positive charged atoms was not as dispersed as in the Pudding Model. Instead, Rutherford guessed that they should be concentrated in a very small volume in the center. This specific portion of Rutherford’s model still holds even up to this day.[viii]
As a result in was time to modify J.J Thomas model of the atom. If Thomson's model is correct then there would be little to nothing to deflect the alpha particle back because all the mass is spread out. Rutherford Concluded that only a positively charged and relatively heavy target particle, such as the proposed nucleus, could account for such strong repulsion. The negative electrons that balanced electrically to the positive nuclear charge were regarded as traveling in circular orbits about the nucleus. The electrostatic force of attraction between electrons and nucleus was related to the gravitational force of attraction between the revolving planets and the Sun. Most of this planetary atom was open space and offered no resistance to the passage of the alpha particles. [ix]
Apart from Rutherford’s work with the atomic structure h has enabled further progress in chemistry and in science. Scientist Neils Bohr developed on what Rutherford atom structure. Bohr saw that the flaw in Rutherford's model is that it contains charges that are accelerating. The charges are on the electrons and the acceleration is due to the electrons always changing direction as they move around their orbits. He realised that electrons inside atoms can't radiate energy continuously.[x] Therefore, Bohr established his own atomic model which was more accurate, derived from Rutherford’s model.
Rutherford has also been acknowledging as the man who paved the way for spitting an atom. Also known as nuclear fission. He bombarded radioactive uranium with neutrons to split the uranium nucleus in half and release huge amounts of energy.[xi] As the nucleus is halved, it emitted extra neutrons which spin off and split more uranium nuclei, creating still more energy and setting off a chain reaction.[xii] James Chadwick who was working under Rutherford at the time did further research into Rutherford’s discovery which led to nuclear plants
producing nuclear energy, and the atomic bomb. He adapted a device he had developed back in New Zealand, using it to detect electro-magnetic waves, and in 1896 succeeded in detecting waves over several hundred meters. This was used to detect Submarines in World War 2.[xiii]
Rutherford also became interested in radioactivity after radioactive atoms were discovered in 1896. He discovered that radioactive atoms gave off two different types of rays alpha and beta. From this he discovered radon, a radioactive gas. From this Rutherford developed a method for working out the age of material such as rocks by measuring the amount of radioactive decay that has taken place, that is, the amount of radioactive material being tested. [xiv]
Rutherford's work has led to some important practical applications in the 21st century including big advances in the field of medicine. Understanding the nucleus and radioactivity has led to many diagnostic techniques for medicine like positron emission tomography, or the radiotherapy cancer treatments that people receive.[xv]
[i] Encyclopedia Britannica. 2013. Thomson atomic model. [online] Available at:
http://www.britannica.com/EBchecked/topic/593128/Thomson-atomic-model
[Accessed: 10 Mar 2014].
[ii] CARL VILLANUEVA, J. 2009. Plum Pudding Model. [online] Available at:
http://www.universetoday.com/38326/plum-pudding-model/ [Accessed: 10 Mar
2014].
[iii] Chalmers, A. 2014. The Rutherford
Journal - The New Zealand Journal for the History and Philosophy of Science and
Technology. [online] Available at:
http://www.rutherfordjournal.org/article010101.html [Accessed: 11 Mar
2014].
[iv]
Aip.org.
2014. Rutherford's Nuclear World: The Story of the Discovery of the Nucleus | Sections | American institute of Physics. [online] Available at:
http://www.aip.org/history/exhibits/rutherford/sections/alpha-particles-atom.html
[Accessed: 10 Mar 2014].
[v]
Sharwood,
J. and Corrigan, D. 2007. Nelson chemistry. South Melbourne: Thomson
Learning.
[vi] Media, N. 2014. Ernest Rutherford - Biographical. [online] Available at: http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-bio.html [Accessed: 10 Mar 2014].
[vii]
NZEDGE.COM. 2014. Ernest Rutherford. [online] Available at:
http://www.nzedge.com/ernest-rutherford/ [Accessed: 10 Mar
2014].
[viii]
P.Kilman14. [online] Available at:
http://undsci.berkeley.edu/lessons/pdfs/rutherford.pdf [Accessed: 10 Mar
2014].
[ix]
Sharwood, J. and Corrigan, D. 2007. Nelson chemistry. South Melbourne: Thomson
Learning.
[x]
Siegfried, T. 2013. When the atom went quantum: Bohr's revolutionary atomic theory turns
100. Science News, 184
(1), pp. 20--24.
[xi]
Chalmers, A. 2014. The Rutherford
Journal - The New Zealand Journal for the History and Philosophy of Science and
Technology. [online] Available at:
http://www.rutherfordjournal.org/article010101.html [Accessed: 11 Mar
2014].
[xii]
Vigyanprasar.gov.in. 2014. Ernest Rutherford. [online] Available at:
http://www.vigyanprasar.gov.in/scientists/ERutherford.htm [Accessed: 10 Mar
2014].
[xiii]
Media,
N. 2014. Ernest Rutherford - Biographical. [online] Available at:
http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-bio.html
[Accessed: 10 Mar 2014].
[xiv]
Christchurchcitylibraries.com. 2014. Ernest Rutherford - Kids - Christchurch City Libraries. [online] Available at:
http://christchurchcitylibraries.com/kids/famousnewzealanders/ernest.asp
[Accessed: 12 Mar 2014].
[xv]
Chemheritage.org. 2014. Ernest Rutherford | Chemical Heritage Foundation. [online]
Available at:
http://www.chemheritage.org/discover/online-resources/chemistry-in-history/themes/atomic-and-nuclear-structure/rutherford.aspx
[Accessed: 10 Mar 2014].