Rutherford Atomic Theory

Dhristi JEE 2022-24

About Rutherford

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.  

 

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 number 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. 

 

We know that an atom's structure is made up of electrons, protons, and neutrons. This was accurately presented after several scientists developed various models. Ernest Rutherford developed the Rutherford atomic model, also known as the Rutherford model of the atom. However, it is no longer considered an accurate representation of an atom. Please tell us more about this model. 


The Rutherford Atomic Model   

Rutherford proposed that an atom is mostly made up of space, with electrons orbiting in predetermined paths around a fixed, positively charged nucleus. 


History 

Democritus, a Greek philosopher, first proposed the concept of the atom in 400 BCE. However, it wasn't until 1803 that John Dalton proposed the idea of the atom again. Atoms were thought to be indivisible at the time. This concept of an atom as indivisible particles persisted until 1897, when British physicist J.J. Thomson discovered negatively charged particles known as electrons.


Based on that, he proposed a model in which electrons were embedded uniformly in a positively charged matrix. The plum pudding model was given that name. J.J. Thomson's plum pudding model, on the other hand, had some limitations. It was unable to explain certain experimental results relating to element atomic structure. 


"Ernest Rutherford," a British physicist, proposed a model of atomic structure known as Rutherford's Model of Atoms. He conducted an experiment in which he bombarded -particles in a thin gold sheet. He investigated the trajectory of the -particles after interaction with the thin sheet of gold in this experiment. 


Experiment with the Rutherford Atomic Model 

In Rutherford's experiment, he bombarded a thin gold foil with high-energy streams -particles. A radioactive source was used to direct the streams of -particles. He conducted experiments to investigate the defect created in the trajectory of -particles after interaction with a thin sheet of gold. To investigate the deflection, he surrounded the gold foil with a zinc sulphide screen. J.J. Thomson's plum pudding model was contradicted by Rutherford's observations. 


Rutherford Model Experiment Results 

Rutherford concluded that major space in an atom is empty based on his observations during the experiment – a large fraction of -particles passed through the gold sheet without being deflected. As a result, the majority of an atom must be empty. 


The positive charge in an atom is not distributed uniformly and is concentrated in a very small volume – When bombarded, the gold sheet deflected a few -particles. They were deflected at minute and small angles. As a result, he came to the above conclusion. 


Very few -particles had been deflected at large angles or returned. Furthermore, only a few particles had deflected at 180o. As a result, he concluded that positively charged particles covered a small proportion of an atom's total volume.


Rutherford atomic model postulates based on observations and conclusions


Positively charged particles make up an atom. The majority of an atom's mass is concentrated in a very small region. The nucleus of an atom was named after this region of the atom. Later, it was discovered that the very small and dense nucleus of an atom is made up of neutrons and protons. 


The nucleus of an atom is surrounded by negatively charged particles known as electrons. At a very high speed, electrons revolve around the nucleus in a fixed circular path. Orbits were named after these fixed circular paths. 


Because electrons are negatively charged and the densely concentrated nucleus is positively charged, an atom has no net charge or is electrically neutral. The nucleus and electrons are held together by a strong electrostatic force of attraction. 


The size of an atom's nucleus is very small in comparison to the total size of an atom.   

  

Rutherford Atomic Model Limitations 

Certain things could not be explained by Rutherford's experiment. They are as follows: 


Rutherford's model was unable to explain atomic stability. According to Rutherford's postulate, electrons revolve at a very high speed in a fixed orbit around an atom's nucleus. Maxwell, on the other hand, explained that accelerated charged particles emit electromagnetic radiations. As a result, electrons revolving around the nucleus emit electromagnetic radiation. 


The electromagnetic radiation will contain energy from the electronic motion, causing the orbits to gradually shrink. Finally, the orbits in an atom's nucleus will contract and collapse. If Maxwell's explanation is followed, Rutherford's model will collapse in 10-8 seconds, according to the calculations. As a result, Rutherford's atomic model did not conform to Maxwell's theory and was unable to explain the stability of an atom. 


Rutherford's theory was lacking in detail because it did not address the arrangement of electrons in the orbit. One of the major flaws of the Rutherford atomic model was this. 


Conclusion 

Despite the fact that early atomic models were inaccurate and could not adequately explain the structure of atoms and experimental results. However, it served as the foundation for quantum mechanics and aided in its future development. 

FAQs on Rutherford Atomic Theory

1. Describe the Rutherford Atomic Model in detail.

An atom is made up of a positively charged, dense, and extremely small nucleus, which contains protons and neutrons, among other elements. In an atom, the nucleus accounts for nearly all of the total mass of the atom. The nucleus is surrounded by electrons that are negatively charged. The electrons are orbiting around the nucleus in orbicular paths at extremely high speeds, following orbicular paths around the nucleus. Orbits are the circular paths taken by electrons as they travel through space. When the number of protons and electrons in an atom equals the number of electrons, the atom is considered electrically neutral. When compared to the nucleus, the atom is significantly larger in size. By bombarding high-energy gamma-ray particles onto a thin gold foil, Rutherford's model experiment was successfully completed. It was a radioactive source that was used to generate the -particles. He carried out the experiment in order to determine the amount of deflection generated in the trajectory of the -particles as a result of their interaction with the thin sheet of gold. Rutherford's model contradicted and improved on JJ Thompson's plum in a pudding model, which had been previously published.

2. Describe the Rutherford model of atom observation in detail.

The Rutherford Observations are the correct answer. During the experiment, a model of an atom was created to demonstrate that a significant amount of space in an atom is empty. A significant proportion of the -particles passed through the gold sheet without being deflected by the gold sheet. As a result, the interior of an atom must be mostly devoid of matter. The positive charge in an atom is not dispersed evenly throughout the atom, and it is concentrated in a small volume – the nucleus. When bombarded with -particles, the gold sheet was able to deflect a small number of them. Minimal angles and small deflections were used to deflect them. As a result, he made the observation described above. There were a disproportionately small number of -particles that were deflected at large angles. Furthermore, only a small number of particles had deflected at an angle of 180°. Therefore, he concluded that the positively charged particles accounted for only a small proportion of the total volume of an atom when compared to the total volume of an atom.

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