Rutherford atomic model and its limitations

Rutherford Atomic Model And Its Limitations

Edited By Shivani Poonia | Updated on Jul 02, 2025 05:49 PM IST

The famous Rutherford's Alpha Scattering Experiment, which clarifies the fundamentals of atomic structure, was conducted by Ernest Rutherford. Using a radioactive source, Rutherford directed high-energy streams of α-particles towards a 100 nm-thick gold sheet. We can learn about the atomic structure from the deflection of these alpha particles. To find out how the alpha particles were deflecting the thin gold foil, he placed a fluorescent zinc sulphide screen around it.

This Story also Contains

Rutherford's Alpha Adventure: Unveiling What's Inside the Atom?
Observations of the Rutherford's Experiment:
Rutherford's Atomic Model's Conclusion:
Limitations of the Rutherford's Model:
Solved Examples Based On Rutherford's α Scattering Experiment
Conclusion

Rutherford Atomic Model And Its Limitations

In this article, we will cover the concept of Rutherford's Alpha particle Experiment, observations including the conclusion based on the experiment. This concept falls under the broader category of Atomic structure, which is a crucial chapter in Class 11 chemistry. It is not only essential for board exams but also for competitive exams like the Joint Entrance Examination (JEE Main), National Eligibility Entrance Test (NEET), and other entrance exams such as SRMJEE, BITSAT, WBJEE, BCECE and more.

Let us study in detail the famous experiment conducted by Rutherford to gain insights into this topic and solve a few related problems.

Rutherford's Alpha Adventure: Unveiling What's Inside the Atom?

A stream of high-energy α–particles from a radioactive source was directed at a thin foil (thickness ∼ 100 nm) of gold metal. The thin gold foil had a circular fluorescent zinc sulphide screen around it. Whenever α–particles struck the screen, a tiny flash of light was produced at that point

Alpha gold foil experiment

Observations of the Rutherford's Experiment:

Most of the α–particles passed through the gold foil undeflected indicating that most of the atom is space.
A small fraction of the α–particles was deflected by small angles indicating that the positive charge is concentrated in a minimal volume.
Very few α–particles (∼1 in 20,000) bounced back, that is, were deflected by nearly 180° thus confirming the size of the nucleus to be very small.

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Rutherford's Atomic Model's Conclusion:

Most of the part of the atom is empty and the atom is spherical.
Each atom consists of a small, heavy, positively charged portion located at the centre, known as the nucleus.
All positive charge of atoms (i.e. protons) are present in the nucleus and electrons move around the nucleus in circular orbits.
Electrons and the nucleus are held together by electrostatic forces of attraction.

Limitations of the Rutherford's Model:

According to Maxwell's theory, a moving charged particle under acceleration radiates energy and thus the electron must spiral into the nucleus, but that does not occur. The stability of the atom was not explained by Rutherford's model.
Rutherford's model does not provide any information about the position of the electron or its energy.

Solved Examples Based On Rutherford's α Scattering Experiment

Example 1: If the Thomson model of the atom was correct, then the result of Rutherford's gold foil experiment would have been :

1) All of the α-particles pass through the gold foil without a decrease in speed.
2) α-Particles are deflected over a wide range of angles.
3) All α-particles get bounced back by 180∘
4) (correct) α-Particles pass through the gold foil deflected by small angles and with reduced speed.

Solution

Thomson's model is similar to a Plum pudding model in which the electrons are embedded in a positively charged sphere.

If this model were correct, Rutherford's gold foil experiment would have observed the alpha particles pass through the gold foil deflected by small angles and with reduced speed.

Hence, the answer is the option (4).

Example 2: Assertion: Rutherford's atomic model failed to explain the stability of an atom.

Reason: According to Rutherford's atomic model, electrons revolve around the nucleus in circular orbits, but such an arrangement would lead to the acceleration of electrons and ultimately cause the atom to collapse.

(1) (correct) Both assertion and reason are true, and the reason is the correct explanation of the assertion.

(2) Both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(3) The assertion is true, but the reason is false.
(4) The assertion is false, but the reason is true.

Solution

According to Rutherford's atomic model, the electrons revolve around the nucleus in circular orbits, similar to planets orbiting around the sun. However, the model could not explain why the electrons did not emit energy continuously and eventually fell into the nucleus. In classical mechanics, any charged particle undergoing acceleration emits radiation, which causes the particle to lose energy, ultimately causing it to spiral into the nucleus. This limitation was resolved by the development of quantum mechanics, which explained that the electrons exist in discrete energy levels and not in fixed orbits.

Hence, the answer is the option (2).

Example 3: What are the limitations of Rutherford's atomic model?

1) It failed to explain the stability of an atom.
2) It could not explain the spectra of atoms with more than one electron.
3) It did not provide any information about the arrangement of electrons in the atom.
4) All of the above.

Solution

Correct option d) All of the above.

Rutherford's atomic model was a significant improvement over the previous atomic models, but it had some limitations. Firstly, it could not explain the stability of an atom. According to classical mechanics, any charged particle undergoing acceleration emits radiation, which causes the particle to lose energy, ultimately causing it to spiral into the nucleus. Secondly, the model could not explain the spectra of atoms with more than one electron. Lastly, the model did not provide any information about the arrangement of electrons in the atom. These limitations were later resolved by the development of quantum mechanics.

Hence, the answer is the option (4).

Conclusion

Based on his findings, Rutherford postulated the atomic structure of the elements. Rutherford's atomic model states that: A positively charged particle was concentrated in a very small volume, which also contained the majority of an atom's mass. He referred to this as an atom's nucleus. Rutherford asserted that atom nuclei are surrounded by negatively charged electrons. The electron that envelops the nucleus travels quickly in a circular pattern. He gave these circular routes names for their orbits.

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Frequently Asked Questions (FAQs)

1. Name a particle and give its location in the atom, which has no charge and has a mass nearly equal to that of a proton.

The particle which has no charge and has a mass nearly equal to that of a proton is a neutron, and it is present in the nucleus of the atom.

2. What was the date of the Rutherford experiment?

Ernest Rutherford's 1909 experiment on the scattering of alpha particles.

3. What was the purpose of the experiment on alpha particle scattering?

The purpose of this experiment was to determine the atom's structure.

4. How is the Rutherford experiment used in the present era?

Although Rutherford's experiment has potential implications in the present era, it also broadened the inventor's perspective on adjacent subjects including nuclear physics, particle physics, and material science. A device called a particle accelerator, which is based on this experiment, is employed in many different types of research.

5. How thick was the gold foil sheet that was utilized in the experiment?

A thin gold sheet for the experiment, a 100 nm thin sheet, was used.

6. How does the Rutherford model differ from the Thomson (plum pudding) model?

The Rutherford model differs significantly from the Thomson model. While the Thomson model proposed that electrons were embedded in a positively charged "pudding," the Rutherford model introduced the concept of a small, dense nucleus with electrons orbiting around it in mostly empty space. This new model explained the results of the gold foil experiment, which the Thomson model could not.

7. What is the main limitation of the Rutherford atomic model regarding electron stability?

The main limitation of the Rutherford model regarding electron stability is that it doesn't explain why electrons don't spiral into the nucleus. According to classical electromagnetic theory, orbiting electrons should continuously lose energy and eventually collapse into the nucleus, but this doesn't happen in reality. This limitation was later addressed by the Bohr model and quantum mechanics.

8. What assumption about electron behavior in the Rutherford model was later proven incorrect?

The Rutherford model assumed that electrons orbit the nucleus in circular paths, similar to planets orbiting the sun. This assumption was later proven incorrect by quantum mechanics, which showed that electrons exist in probability clouds called orbitals, rather than in definite circular orbits.

9. How did the Rutherford model contribute to our understanding of isotopes?

The Rutherford model contributed to our understanding of isotopes by introducing the concept of the nucleus. This led to the realization that atoms of the same element could have different numbers of neutrons in their nuclei while maintaining the same number of protons, explaining the existence of isotopes.

10. How did the Rutherford model contribute to our understanding of isotopes?

The Rutherford model contributed to our understanding of isotopes by introducing the concept of the nucleus. This led to the realization that atoms of the same element could have different numbers of neutrons while maintaining the same number of protons, explaining the existence of isotopes with different atomic masses but identical chemical properties.

11. How did the Rutherford model challenge the idea of atoms being indivisible?

The Rutherford model challenged the long-held belief that atoms were indivisible by proposing that atoms had internal structure. By identifying the nucleus and orbiting electrons, Rutherford showed that atoms were composed of smaller particles, paving the way for the discovery of subatomic particles and the field of particle physics.

12. What is the significance of the "Rutherford scattering" in the context of his atomic model?

Rutherford scattering refers to the deflection of alpha particles by the atomic nuclei in the gold foil experiment. This phenomenon was crucial in developing the Rutherford atomic model, as it provided evidence for the existence of a small, dense, positively charged nucleus and mostly empty space within atoms.

13. How did the Rutherford model explain the results of the gold foil experiment?

The Rutherford model explained the gold foil experiment results by proposing a small, dense, positively charged nucleus. This accounted for the rare but significant deflections of alpha particles, as only a concentrated positive charge could repel the positively charged alpha particles strongly enough to cause large-angle scattering or backscattering.

14. What is the significance of the "mostly empty space" in the Rutherford model?

The concept of atoms being mostly empty space in the Rutherford model is significant because it explains why most alpha particles in the gold foil experiment passed through the foil undeflected. It also helps explain various physical properties of matter, such as compressibility, and laid the groundwork for understanding chemical bonding and atomic interactions.

15. What role did the Rutherford model play in the development of nuclear physics?

The Rutherford model played a crucial role in the development of nuclear physics by introducing the concept of the atomic nucleus. This discovery led to further investigations into nuclear structure, radioactivity, and nuclear reactions, ultimately giving rise to the field of nuclear physics and influencing areas such as nuclear energy and medicine.

16. What did the Rutherford model reveal about the size of the nucleus compared to the atom?

The Rutherford model revealed that the nucleus is extremely small compared to the overall size of the atom. In fact, if an atom were the size of a football field, the nucleus would be about the size of a pea. This discovery of the atom being mostly empty space was a revolutionary concept at the time.

17. How did the Rutherford model contribute to our understanding of atomic size?

The Rutherford model contributed to our understanding of atomic size by revealing that atoms are mostly empty space. It showed that the actual volume occupied by the nucleus and electrons is very small compared to the total volume of the atom, explaining why matter is mostly empty space at the atomic level.

18. How does the Rutherford model account for the neutral charge of an atom?

The Rutherford model accounts for the neutral charge of an atom by proposing that the positive charge of the nucleus is balanced by the negative charge of the orbiting electrons. In a neutral atom, the number of protons in the nucleus equals the number of electrons orbiting it, resulting in a net charge of zero.

19. What is the "planetary model" analogy often used to describe the Rutherford atomic model?

The Rutherford atomic model is often described using the "planetary model" analogy. In this comparison, the nucleus is likened to the sun at the center of a solar system, while the electrons are compared to planets orbiting around it. This analogy helps visualize the basic structure proposed by Rutherford, though it has limitations in accurately representing atomic behavior.

20. What is the main difference between Rutherford's and Bohr's atomic models?

The main difference between Rutherford's and Bohr's atomic models is that Bohr introduced the concept of fixed electron energy levels or shells. While Rutherford proposed electrons orbiting randomly, Bohr suggested that electrons could only exist in specific, quantized energy states, addressing the stability issue in Rutherford's model and explaining atomic spectra.

21. How does the Rutherford model explain the concept of atomic number?

The Rutherford model introduced the concept of a positively charged nucleus, which laid the foundation for understanding atomic number. The atomic number is defined as the number of protons in the nucleus, which Rutherford's model helped identify as the key factor in determining an element's identity.

22. What is the Rutherford atomic model?

The Rutherford atomic model, proposed by Ernest Rutherford in 1911, describes an atom as having a small, dense, positively charged nucleus at the center, surrounded by negatively charged electrons orbiting in mostly empty space. This model was based on Rutherford's famous gold foil experiment and revolutionized our understanding of atomic structure.

23. How did Rutherford's gold foil experiment lead to his atomic model?

Rutherford's gold foil experiment involved firing alpha particles at a thin gold foil. Most particles passed through, but some were deflected at large angles or even bounced back. This unexpected result led Rutherford to conclude that atoms must have a small, dense, positively charged nucleus, with electrons orbiting in mostly empty space, contradicting the previous "plum pudding" model.

24. What are the key features of the Rutherford atomic model?

The key features of the Rutherford atomic model are: 1) A small, dense, positively charged nucleus at the center of the atom, 2) Negatively charged electrons orbiting the nucleus, 3) Mostly empty space between the nucleus and electrons, and 4) The total positive charge of the nucleus balancing the total negative charge of the electrons.

25. Why is the Rutherford model sometimes called the "nuclear model" of the atom?

The Rutherford model is often called the "nuclear model" because it was the first to introduce the concept of a nucleus. This small, dense, positively charged center of the atom became a fundamental aspect of our understanding of atomic structure, leading to the development of nuclear physics and chemistry.

26. How does the Rutherford model explain the mass of an atom?

The Rutherford model explains that most of an atom's mass is concentrated in the small, dense nucleus. This is because protons and neutrons, which make up the nucleus, are much more massive than electrons. The electrons, despite occupying most of the atom's volume, contribute very little to its overall mass.

27. How did the Rutherford model challenge the classical laws of electromagnetism?

The Rutherford model challenged classical electromagnetism by proposing orbiting electrons that, according to classical physics, should continuously emit energy and spiral into the nucleus. This contradiction highlighted the limitations of classical physics in explaining atomic behavior and paved the way for the development of quantum mechanics.

28. What limitation of the Rutherford model is related to atomic spectra?

A major limitation of the Rutherford model is its inability to explain atomic spectra. The model doesn't account for the discrete emission and absorption lines observed in atomic spectra, which were later explained by the Bohr model and quantum mechanics through the concept of quantized energy levels.

29. How does the Rutherford model explain the difference between elements?

The Rutherford model explains the difference between elements based on the positive charge of the nucleus. Different elements have different numbers of protons in their nuclei, which determines their atomic number and chemical properties. This concept laid the groundwork for our modern understanding of elemental identity.

30. What assumption about the distribution of positive charge in an atom did Rutherford's model overturn?

Rutherford's model overturned the assumption that positive charge was evenly distributed throughout the atom, as proposed in Thomson's "plum pudding" model. Instead, Rutherford showed that the positive charge was concentrated in a small, dense nucleus at the center of the atom.

31. How did the Rutherford model contribute to the discovery of the neutron?

The Rutherford model, by introducing the concept of a nucleus, set the stage for the discovery of the neutron. The model's prediction of a positively charged nucleus led to questions about how protons could be held together, ultimately leading to the discovery of neutrons by James Chadwick in 1932.

32. What is the relationship between the Rutherford model and the concept of atomic mass?

The Rutherford model relates to atomic mass by proposing that most of an atom's mass is concentrated in its small, dense nucleus. This concept helped explain why atoms have specific masses and led to the understanding that atomic mass is primarily determined by the number of protons and neutrons in the nucleus.

33. How does the Rutherford model explain the phenomenon of radioactivity?

While the Rutherford model doesn't directly explain radioactivity, it provides a framework for understanding it. By identifying the nucleus as the source of positive charge and most of the atom's mass, it set the stage for explaining radioactivity as a process originating from unstable nuclei, leading to the emission of particles or energy.

34. What aspect of atomic structure did the Rutherford model fail to explain that was later addressed by the Bohr model?

The Rutherford model failed to explain the stability of electron orbits and the discrete nature of atomic spectra. These aspects were later addressed by the Bohr model, which introduced the concept of quantized energy levels for electrons, explaining both the stability of atoms and the discrete lines in atomic spectra.

35. How did the Rutherford model contribute to our understanding of chemical bonding?

The Rutherford model contributed to our understanding of chemical bonding by introducing the concept of electrons orbiting a nucleus. This laid the groundwork for later theories of electron sharing and transfer in chemical bonds, although the model itself didn't directly explain bonding mechanisms.

36. What is the significance of the "nuclear charge" in the Rutherford model?

The nuclear charge in the Rutherford model refers to the total positive charge of the nucleus, which is equal to the number of protons. This concept is significant because it determines the atomic number of an element and plays a crucial role in chemical properties and electron configurations.

37. How does the Rutherford model explain the concept of ionization?

The Rutherford model helps explain ionization by proposing that electrons orbit the nucleus and can be removed from the atom. When an atom loses or gains electrons, it becomes an ion. This model provided a structural basis for understanding how atoms can become electrically charged.

38. What limitation of the Rutherford model is related to the wave nature of electrons?

The Rutherford model doesn't account for the wave nature of electrons, which was later discovered through quantum mechanics. This limitation means the model can't explain phenomena like electron diffraction or the uncertainty in electron position and momentum.

39. How did the Rutherford model influence the development of the periodic table?

The Rutherford model influenced the development of the periodic table by introducing the concept of atomic number (number of protons in the nucleus) as a fundamental property of elements. This led to a more accurate arrangement of elements in the periodic table based on atomic number rather than atomic weight.

40. What aspect of the Rutherford model contradicts the law of conservation of energy?

The Rutherford model contradicts the law of conservation of energy because it predicts that orbiting electrons should continuously emit energy as electromagnetic radiation. According to classical physics, this would cause the electrons to spiral into the nucleus, which doesn't happen in reality.

41. How does the Rutherford model explain the difference in size between an atom and its nucleus?

The Rutherford model explains the vast difference in size between an atom and its nucleus by proposing that atoms are mostly empty space. The nucleus, containing most of the atom's mass, is extremely small compared to the overall atomic volume, which is determined by the space occupied by orbiting electrons.

42. What role did the concept of "cross-section" play in Rutherford's interpretation of his gold foil experiment?

The concept of "cross-section" was crucial in Rutherford's interpretation of the gold foil experiment. It refers to the effective area presented by the nucleus for interaction with alpha particles. The small number of large-angle deflections indicated a very small nuclear cross-section, supporting the idea of a tiny, dense nucleus.

43. How did the Rutherford model challenge the concept of the indivisibility of the atom?

The Rutherford model challenged the concept of the indivisibility of the atom by proposing that atoms have internal structure. By identifying distinct components (nucleus and electrons), it showed that atoms could be further divided, paving the way for the discovery of subatomic particles.

44. What is the significance of the "Rutherford backscattering" in his atomic model?

Rutherford backscattering, where some alpha particles were deflected back towards the source, was crucial evidence for a small, dense, positively charged nucleus. This unexpected observation could only be explained by the presence of a concentrated positive charge capable of strongly repelling the alpha particles.

45. How does the Rutherford model relate to the concept of electron shells?

The Rutherford model doesn't directly address electron shells, which were introduced later by the Bohr model. However, by proposing electrons orbiting the nucleus, it laid the groundwork for more sophisticated models of electron arrangement, eventually leading to the concept of electron shells and orbitals.

46. What limitation of the Rutherford model is related to the prediction of atomic spectra?

The Rutherford model cannot predict or explain atomic spectra. It doesn't account for the discrete emission and absorption lines observed in spectroscopy, which require a quantized model of electron energy levels as later proposed by Bohr and quantum mechanics.

47. What aspect of the Rutherford model was later modified by the discovery of the neutron?

The discovery of the neutron by James Chadwick in 1932 modified the understanding of the nucleus in the Rutherford model. While Rutherford's model correctly identified a positively charged nucleus, the addition of neutrons explained the discrepancy between atomic number and atomic mass, and how protons could be held together in the nucleus despite their mutual repulsion.

48. How does the Rutherford model explain the difference in atomic radii among elements?

The Rutherford model doesn't directly explain differences in atomic radii, which is a limitation of the model. However, it laid the groundwork for understanding that atomic size is related to the number of electron shells and the nuclear charge, concepts that were developed in later atomic models.

49. What is the significance of the "Coulomb barrier" in the context of Rutherford's atomic model?

The Coulomb barrier, the electrostatic repulsion between positively charged particles, became significant in the context of Rutherford's model. It explained why alpha particles needed high energy to approach the nucleus closely, and why nuclear reactions are difficult to initiate, contributing to our understanding of nuclear physics and fusion.

50. How did the Rutherford model contribute to the development of quantum mechanics?

The Rutherford model contributed to the development of quantum mechanics by exposing the limitations of classical physics in explaining atomic structure. The model's inability to explain electron stability and atomic spectra highlighted the need for a new approach, leading to the development of quantum mechanical models of the atom.

51. What is the relationship between the Rutherford model and the concept of electron configuration?

While the Rutherford model doesn't directly address electron configuration, it