Rutherford's Nuclear Model

Rutherford Atomic Theory

Ernest Rutherford was a New Zealand born physicist who in 1911 described the structure of an atom, which was an improvement on the plum in pudding model of atom Rutherford model is also known as the rutherford atomic model, planetary model of the atom, or the nuclear model of the atom. The Rutherford atomic theory has defined the atom as a tiny, dense, positively charged core called a nucleus, which is surrounded by negative charges called electrons. It describes the atomic model as to where all the atom’s mass is concentrated in the centre called the nucleus, around which the negative charges called the electrons revolve. 

Rutherford’s Atomic Model

According to Rutherford’s atomic model, the positively charged particles and most of the atom’s mass was concentrated in a minimal volume. He called this region of the atoms a nucleus. Rutherford’s nuclear model also proposed that the negatively charged electrons encircle the nucleus of an atom. Rutherford also proposed that the electrons move at the speed of light around the nucleus. He named these circular paths orbits. 

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Rutherford Nuclear Model

By improving on Thomson’s model of the atom Rutherford in 1911 depicted that the atom has a dense nucleus with the help of the gold-foil experiment, and thereby improved the understanding of the atomic model. Five years earlier, Rutherford observed that alpha particles transmitted through a hole onto a graphic plate would make a sharp-edged picture. In contrast, alpha particles transmitted through a sheet of mica only 20 micrometres thick would create an effect with blurry edges. For some particles, the blurring resembled a two-degree deflection. Remembering those results, Rutherford had his postdoctoral fellow, Hans Geiger, and an undergraduate student, Ernest Marsden, refined the experiment by beaming alpha particles through gold foil and recognised them as beams of light or scintillations on a screen. 

The gold foil was only 0.00004 cm thick. Most alpha particles went directly through the foil, but some were diverted by the foil and hit the spot on a screen placed off to one side. However, the Rutherford atomic model was not readily accepted by all physicists, as it did not conform to the then chemical understanding of the atom. The model suggested that the charge on the nucleus was the essential characteristic of the atom, determining its structure. On the other hand, Mendeleyev’s periodic table of the elements was organised according to the atomic masses, implying that the mass was responsible for atoms’ structure and chemical behaviour.

Rutherford Atomic Structure

The present-day understanding of the atom is based on the nuclear model of the atom proposed and explained by Rutherford, which says that the atom has a large, dense central mass called the nucleus, which is encircled by the negatively charged electrons. The protons that make up the nucleus are positively charged, and it is represented by Z, the atomic number of an element. For an atom to be electrically neutral, it must cover the same number of extranuclear electrons as there are protons in the nucleus. Hence, the amount of electrons in a neutral atom of atomic number Z is also Z. For example, the hydrogen atom has one proton and one electron, whereas the carbon atom comprises six electrons.

FAQs (Frequently Asked Questions)

Q1. Describe Rutherford Model of an Atom. 

Answer: An atom consists of a positively charged, dense and very small nucleus, including protons and neutrons. The nucleus constitutes almost the entire mass of the atom. Negatively charged electrons surround the nucleus. The electrons are orbiting around the nucleus in orbicular paths at very high speed. These circular paths of the electrons are termed orbits. When the number of protons and electrons are equal, the atom is electrically neutral. The atom is much larger in size compared to the nucleus. Rutherford’s model experiment was conducted by bombarding high-energy α-particles on the gold foil of very little thickness. The α-particles were generated from a radioactive source. He conducted the experiment to analyze the deflection generated in the trajectory of α-particles after interaction with the thin sheet of gold. Rutherford’s model contradicted and improved on JJ Thompson plum in a pudding model.

Q2. Explain Rutherford Model of an Atom Observation. 

Answer: The Observations of the Rutherford Model of an atom made during the experiment explained that significant space in an atom is empty. A substantial fraction of α-particles crossed through the gold sheet without getting deflected. Therefore, the inside of an atom must be mostly empty. The positive charge in an atom is not dispersed uniformly, and it is concentrated in a minimal volume – Few α-particles, when bombarded, were deflected by the gold sheet. They were deflected minutely and at minimal angles. Therefore, he made the above observation. Significantly few α-particles had deflected at large angles. Moreover, very few particles had deflected at 180°. Consequently, he concluded that the positively charged particles comprised a small volume of an atom compared to the total volume of an atom.