Important points of Rutherford atomic model
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In 1911, he was the first to discover that atoms have a small charged nucleus surrounded by largely empty space, and are circled by tiny electrons, which became known as the Rutherford model (or planetary model) of the atom.
Rutherford overturned Thomson's model in 1911 with his well-known gold foil experiment in which he demonstrated that the atom has a tiny and heavy nucleus. Rutherford designed an experiment to use the alpha particles emitted by a radioactive element as probes to the unseen world of atomic structure.
Rutherford's experiment showed that atoms consisted of a dense mass which was surrounded by mostly empty space - the nucleus! Rutherford's experiment utilized positively charged alpha particles (He with a +2 charge) which were deflected by the dense inner mass (nucleus).
Rutherford conducted alpha scattering experiment and put forward a model of atom known as Rutherford's nuclear model. The salient features of this model are as follows: (i) The atom contains a central part called nucleus which is surrounded by electrons. (ii) The nucleus of an atom is positively charged.
Rutherford Atomic Model
Rutherford proposed that an atom is composed of empty space mostly with electrons orbiting in a set, predictable paths around fixed, positively charged nucleus.
Rutherford's Model of an Atom
Rutherford’s Atomic Model (Source Credit: Britannica)
History
The concept of atom dates back to 400 BCE when Greek philosopher Democritus first conceived the idea. However, it was not until 1803 John Dalton proposed again the idea of the atom. But at that point of time, atoms were considered indivisible. This idea of an atom as indivisible particles continued until the year 1897 when British Physicist J.J. Thomson discovered negatively charged particles which were later named electrons.
Learn more about the Structure of Atom in more detail here
He proposed a model on the basis of that where he explained electrons were embedded uniformly in a positively charged matrix. The model was named plum pudding model. However, J.J. Thomson’s plum pudding model had some limitations. It failed to explain certain experimental results related to the atomic structure of elements.
A British Physicist “Ernest Rutherford” proposed a model of the atomic structure known as Rutherford’s Model of Atoms. He conducted an experiment where he bombarded α-particles in a thin sheet of gold. In this experiment, he studied the trajectory of the α-particles after interaction with the thin sheet of gold.
Rutherford Atomic Model Experiment
In Rutherford’s experiment, he bombarded high energy streams of α-particles on a thin gold foil of 100 nm thickness. The streams of α-particles were directed from a radioactive source. He conducted the experiment to study the deflection produced in the trajectory of α-particles after interaction with the thin sheet of gold. To study the deflection, he placed a screen made up of zinc sulfide around the gold foil. The observations made by Rutherford contradicted the plum pudding model given by J.J. Thomson.
rutherford atomic model, Rutherford Gold foil experiment
Rutherford’s Gold Foil Experiment (Source Credit: Britannica)
Observations of Rutherford Model Experiment
On the basis of the observations made during the experiment, Rutherford concluded that
Major space in an atom is empty – A large fraction of α-particles passed through the gold sheet without getting deflected. Therefore, the major part of an atom must be empty.
The positive charge in an atom is not distributed uniformly and it is concentrated in a very small volume – Few α-particles when bombarded were deflected by the gold sheet. They were deflected minutely and at very small angles. Therefore he made the above conclusion.
Very few α-particles had deflected at large angles or deflected back. Moreover, very few particles had deflected at 180o. Therefore, he concluded that the positively charged particles covered a small volume of an atom in comparison to the total volume of an atom.
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