Rutherford model
The Rutherford model, introduced by physicist Ernest Rutherford in 1911, represents a significant advancement in the understanding of atomic structure. This model posits that atoms are primarily composed of empty space, with a dense, positively charged nucleus at the center containing protons, while negatively charged electrons orbit around this nucleus, similar to how planets orbit the sun. The model emerged from Rutherford’s famous gold foil experiment, where he observed that some alpha particles deflected unexpectedly, indicating the presence of a compact core within the atom, contradicting the previously accepted "plum pudding" model proposed by J.J. Thomson.
The Rutherford model fundamentally changed the perception of atomic structure and laid the groundwork for future developments in atomic theory. Although it was later refined by scientists like Niels Bohr, who incorporated quantum theory, the Rutherford model remains a crucial part of the historical narrative of atomic science. This model not only highlights the complex nature of matter but also reflects the evolving landscape of scientific inquiry and understanding in physics and chemistry. The exploration of atomic structure continues to inspire diverse perspectives and research in contemporary science.
Rutherford model
The Rutherford model is a model of atomic structure first introduced by physicist Ernest Rutherford in 1911. In contrast to other theories of atomic structure available at the time, the Rutherford model advanced the notion that atoms are mostly empty space. It proposed that a highly concentrated, positively charged core sits at the center of an atom and that negatively charged particles orbit the core at a distance, much like the planets orbit the sun. The Rutherford model has since been refined, but it has remained a significant model of atomic structure over time.
Life of Rutherford
Born August 30, 1871, near Nelson, New Zealand, Ernest Rutherford developed an early interest in science, which he pursued with fervor throughout secondary school. After winning a scholarship, he continued his education at Canterbury College in Christchurch, New Zealand, in 1889. He earned numerous degrees before winning another scholarship and the opportunity to study under renowned physicist J.J. (Joseph John) Thomson at Cambridge University.
Under Thomson's tutelage, Rutherford devoted himself to research on various topics such as magnetism and X-rays. In 1898, Rutherford accepted a professorship at McGill University in Montreal, Quebec, Canada, where he taught physics. During this time, Rutherford conducted investigations into radioactivity, which ultimately led to his winning the Nobel Prize in chemistry in 1908.
Rutherford returned to England in 1907 to serve as the director of the physics laboratory at Manchester University. There, Rutherford conducted the famous gold foil experiment that ultimately led to his proposal of a new model of atomic structure in 1911.
Rutherford remained a leader in his field throughout the remainder of his career and won numerous honors and awards. Rutherford died October 19, 1937, in Cambridge, England.
Models of Atomic Structure
An atom is the smallest unit of matter that can exist by itself. However, atoms are composed of even smaller units, called subatomic particles. Subatomic particles include protons, which carry a positive charge; electrons, which carry a negative charge; and neutrons, which are neutral and have no charge.
From the middle of the nineteenth century to the early years of the twentieth century, scientists advanced a number of different models to explain the arrangement of protons and electrons within an atom. One of the most well-known arrangements, proposed by J.J. Thomson, was known as the "plum pudding" model. Thomson imagined the atom as an evenly distributed sphere of positive particles with negative particles scattered equally throughout (like raisins sprinkled in a Christmas pudding). The result, according to Thomson, was a neutral atom.
In 1909, Rutherford decided to conduct an experiment to test Thomson's premise. Earlier in his career, Rutherford had identified tiny, positively charged particles, called alpha (α) particles, which are emitted as radioactive materials break down. Rutherford believed that if Thomson's "plum pudding" model of the atom was accurate, an atom's mass had to be evenly dispersed. In theory, a beam of positively charged alpha particles fired at a thin film of neutral gold atoms should pass through the film nearly unhindered.
Rutherford and his assistant, Hans Geiger, along with undergraduate student Ernest Marsden, designed an experiment in which they fired alpha particles at an incredibly thin sheet of gold foil and tracked their trajectories. The scientists expected the alpha particles to easily pass through the foil. All were astounded when a few alpha particles bounced off the foil—as if they had hit something solid—and returned toward them. The results disproved Thomson's plum pudding model and led to a new hypothesis.
Rutherford's Model
Two years after the gold foil experiment, Rutherford introduced his new model of atomic structure. He proposed that an atom is mostly empty space, but it has a dense, positively charged core (later termed the nucleus), which contains all of the atom's protons and the majority of its mass. Negatively charged electrons, which have very little mass, orbit the nucleus at a distance. Comparison of electrons' orbits around the nucleus of an atom to the planets' orbits around the sun has led some to term Rutherford's model the "planetary model" of the atom.
Rutherford explained that the reason why a few alpha particles in the gold foil experiment bounced backward was because they had approached the relatively solid, positively charged nucleus of a gold atom. Because like charges repel each other, the positively charged gold nuclei pushed the positively charged alpha particles away. As a result, those few alpha particles returned in the opposite direction from which they had been fired instead of passing through the foil. The rest of the alpha particles passed through the mostly empty space of the gold atoms in the thin sheet of foil.
The Rutherford model revolutionized the way scientists thought about atomic structure. Some, however, remained skeptical, which led to further investigation and refinement of the model. In 1912, for example, Danish physicist Niels Bohr used quantum theory to identify atomic structure and explain the plausibility of the Rutherford model. This led to a modification known as the Bohr-Rutherford model of atomic structure. Since then, scientists have continued to fine-tune the theory, but both the Rutherford and Bohr-Rutherford models have maintained their status as important advancements in the fields of physics and chemistry.
Bibliography
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Badash, Lawrence. "Rutherford, Ernest." Building Blocks of Matter: A Supplement to the Macmillan Encyclopedia of Physics. Ed. John S. Rigden. New York, Macmillan Reference USA: 2003. 423–426. Print.
Ede, Andrew. "Rutherford, Ernest." Chemistry: Foundations and Applications. Ed. J.J. Lagowski. Vol. 4. New York, Macmillan Reference USA: 2004. 98–100. Print.
"Rutherford's Experiment and Atomic Model." Encyclopedia of Science. The Worlds of David Darling. Web. 3 Dec. 2014. http://www.daviddarling.info/encyclopedia/R/Rutherfords‗experiment‗and‗atomic‗model.html
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"A Science Odyssey: People and Discoveries: Rutherford and Bohr Describe Atomic Structure." PBS. WGBH. Web. 3 Dec. 2014. http://www.pbs.org/wgbh/aso/databank/entries/dp13at.html