All questions of Atoms for A Level Exam

Correct Option C ===>ΔΔΔ ΔAlfa particles are massive particles and they have speed when they bombarded.... ΔAccording plum pudding model if atom given by Thomson protons and electrons are equally distributed.... Δthat's why massive alpha particles will pass through the foil with little deflection (due to protons)...... ΔBcoz here protons are like spreaded cloud and not in nucleus ( massive part or atom) .... Δand alpha particle is more massive than single proton....so they will not deflect due to protons and will pass through foil....

**Explanation:**

The correct answer is **a) The alpha particles used in Rutherford's experiment are positively charged particles**.

Rutherford's experiment, also known as the gold foil experiment, was conducted in 1909 by Ernest Rutherford and his colleagues Hans Geiger and Ernest Marsden. The experiment aimed to understand the structure of the atom and investigate the distribution of positive charge within it.

In this experiment, Rutherford and his team bombarded a thin gold foil with a beam of alpha particles. Alpha particles are positively charged particles that consist of two protons and two neutrons, which are the same as helium nuclei. They are emitted from a radioactive source, such as radium or polonium.

Rutherford observed that while most of the alpha particles passed straight through the gold foil, some of them were deflected at different angles, and a very small fraction bounced back in the direction opposite to the source. This unexpected result led to the discovery of the atomic nucleus and the concept of a mostly empty space within the atom.

Based on the observations from the experiment, Rutherford proposed a new atomic model known as the nuclear model. According to this model, atoms have a dense, positively charged nucleus at the center, which contains most of the atom's mass. The electrons, which are negatively charged particles, orbit around the nucleus in specific energy levels.

Therefore, the correct answer is a) The alpha particles used in Rutherford's experiment are positively charged particles.

C)h/π
d)h

The correct answer is d) h.

The angular momentum of an electron in the hydrogen atom is given by the formula L = nħ, where n is the principal quantum number and ħ is the reduced Planck constant.

In the lowest energy state, the electron is in the ground state with n = 1. Therefore, the angular momentum is L = 1ħ = h.

Explanation:

The Geiger-Marsden experiment was conducted to study the structure of an atom. In this experiment, a beam of alpha particles was directed towards a thin gold foil. The alpha particles were expected to pass through the gold foil with little or no deflection, as it was believed that the positive charge and the negative electrons in an atom are distributed uniformly, reducing the electric field inside the atom. However, the results of the experiment were surprising, as some of the alpha particles were deflected at large angles, and some even bounced back.

Reasons for very small deflection of the beam:

- Electrical forces: According to Coulomb's law, any two charged particles exert a force on each other. In an atom, the positively charged nucleus and the negatively charged electrons are attracted to each other by electrical forces. However, the electrons are in constant motion, creating a cloud of negative charge around the nucleus. This cloud of negative charge reduces the electric field inside the atom, making it difficult for the alpha particles to be deflected.
- Distribution of charge: The positive charge in an atom is concentrated in the nucleus, while the negative charge is distributed throughout the atom. This distribution of charge makes the electric field inside the atom more uniform, reducing the chances of the alpha particles being deflected.
- Collimation of particles: The alpha particles were collimated by lead screens before they were directed towards the gold foil. This was done to ensure that the particles were traveling in a straight line and were not scattered by other particles or objects in the environment.
- Most particles pass through: Despite the above factors, it was still expected that some of the alpha particles would be deflected at small angles due to the random nature of the collisions between the particles and the atoms in the gold foil. However, it was not expected that some of the particles would be deflected at large angles or bounce back, as this implied that the positive charge in an atom was not uniformly distributed.

Conclusion:

In conclusion, the very small deflection of the beam was expected in the Geiger-Marsden experiment due to the distribution of charge in an atom and the reduction of electric field inside the atom. However, the unexpected results of the experiment led to the discovery of the nucleus and the development of the modern atomic model.

Answer is D

Answer is A
E2-E1=hv

A/C to Bohr model ... mvr=nh/2π ... n=1,2,3...

It's Rutherford alpha Ray scattering experiment.....in this experiment gold foil was used...

The kinetic energy is zero and the electrical potential equals the initial kinetic energy supplied

If that is so grant us some suggestion! Or Balmer sequence (2nd sequence from electrons laying off to n = 2 from bigger than 2) longest wavelength [velocityconstant = frequency x wavelength] is smallest frequency [power = hconstant x frequency] is least enegy is from transition n = 3 to n = 2 or Google it 656.3 nm

Rutherford confirmed that the repulsive force of α- particles due to the nucleus varies with distance according to inverse square law and that the positive charges are concentrated at the centre and not distributed throughout the atom.

Bohr postulated that electrons in stationary orbits around the nucleus do not radiate. This is the one of Bohr’s postulates, According to this the moving electrons radiate only when they go from one orbit to the next lower orbit.

Assertion and Reason Overview
The question involves analyzing the assertions made by Bohr about electron behavior and the classical physics perspective on electron radiation.
Assertion (A):
Bohr proposed that electrons in stationary orbits around the nucleus do not radiate energy. This is a fundamental tenet of Bohr's model of the atom, which introduced quantized energy levels.
Reason (R):
According to classical physics, any charged particle in motion, such as an electron, should radiate energy in the form of electromagnetic radiation. This would lead to a loss of energy and result in the electron spiraling into the nucleus, which contradicts the stability of atoms.
Analysis of the Statements
- True Nature of A:
- Bohr's assertion is indeed true. His model successfully explains the stability of atoms by introducing the concept of stationary orbits where electrons do not radiate energy.
- True Nature of R:
- The reason is also true in the context of classical physics. According to classical theories, electrons in motion should emit radiation due to acceleration.
Explanation of the Correct Choice
- Option B - Both A and R are true but R is NOT the correct explanation of A:
- While both assertions are true, the reason does not serve as a correct explanation for Bohr's postulate. Bohr's model was a breakthrough that specifically addressed the limitations of classical physics, providing a new framework for understanding atomic structure.
Conclusion
Thus, the correct choice is option B, as both statements are valid, but the classical reasoning does not adequately explain the Bohr model's assertion regarding stationary orbits.

Bohr Model Hypothesis and Stable Electron Orbit

Bohr model hypothesis is a model of the atom proposed by Niels Bohr in 1913. It was one of the earliest attempts to explain the structure of atoms and their behavior. The model was based on the assumption that electrons orbit the nucleus in circular paths.

The correct statement about Bohr model hypothesis is:

- Electron in a stable orbit does not radiate electromagnetic waves.

Explanation:

- Electrons in atoms can exist only in certain discrete energy levels. According to Bohr's model, electrons in atoms move around the nucleus in stable orbits, each with a specific energy level.
- Electrons in stable orbits do not emit electromagnetic waves because they are in a stable state and have a fixed amount of energy.
- However, when an electron transitions from a higher energy level to a lower energy level, it emits a photon of light.
- This is because the energy lost by the electron is emitted as a photon of light. The energy of the photon is equal to the difference in energy between the two energy levels.
- Therefore, the Bohr model hypothesis proposed that the electron does not continuously lose energy as it moves in a circular orbit around the nucleus, but instead only loses energy when it transitions between energy levels.

Conclusion:

Bohr model hypothesis is an important model that helps explain the behavior of atoms. The model is based on the assumption that electrons move around the nucleus in stable orbits and only emit electromagnetic waves when they transition between energy levels. The correct statement about the model is that electrons in a stable orbit do not radiate electromagnetic waves.

Explanation:

Bohr model is not applicable for multi-electron models because it was developed for hydrogen atom, which has only one electron. As we move to elements with more than one electron, the Bohr model fails to accurately predict the behavior of these atoms.
However, the reason for this limitation is that Bohr model cannot account for sublevel (s, p, d, f) orbitals and electron spin. These concepts are crucial in understanding the behavior of multi-electron atoms.
Therefore, both the Assertion and Reason are true, and the Reason provides a correct explanation for why the Bohr model is not applicable for multi-electron models.

Rutherford Alpha Particle Scattering Experiment.Rutherford directed beams of alpha particles (which are the nuclei of helium atoms and hence positively charged) at thin gold foil to test this model and noted how the alpha particles scattered from the foil.

When he sent alpha particles during his gold foil experiment he observed that most of the rays moved away from the nucleus.As we know that like charges always repel ,he concluded that the charge the nuclei is same as the charge of alpha particles

Assertion (A): According to Rutherford, the atomic model, the path of electrons is parabolic.

Reason (R): Rutherford could not explain the stability of atoms.

The correct answer is option D, which states that Assertion (A) is false and Reason (R) is true.

Explanation:
- The atomic model proposed by Ernest Rutherford is known as the Rutherford model or the planetary model of the atom. According to this model, the atom consists of a small, dense, positively charged nucleus at the center and electrons moving in circular orbits around the nucleus.

Assertion (A) - According to Rutherford, the atomic model, the path of electrons is parabolic:
- The assertion is false. According to the Rutherford model, the path of electrons is not parabolic but circular. The electrons move in circular orbits around the nucleus, similar to the planets orbiting the sun in our solar system.

Reason (R) - Rutherford could not explain the stability of atoms:
- The reason is true. Although the Rutherford model provided a significant advancement in understanding the structure of atoms, it could not explain the stability of atoms. According to classical electromagnetism, an accelerated charged particle should emit electromagnetic radiation and lose energy, resulting in the collapse of the electron orbits. If this were true, atoms would not be stable, and matter as we know it would not exist.
- However, in reality, atoms are stable, and matter is observed to be persistent. This stability of atoms could not be explained by the classical electromagnetic theory, leading to the development of quantum mechanics, which provides a more accurate description of the behavior of electrons in atoms.

In conclusion, the assertion that the path of electrons in the Rutherford model is parabolic is false. Additionally, Rutherford's model could not explain the stability of atoms, which led to the development of quantum mechanics.

When the atom gets appropriate energy from outside, then this electron rises to some higher energy level. Now it can return either directly to the lower energy level or come to the lowest energy level after passing through other lower energy levels hence all possible transitions take place in the source and many lines are seen in the spectrum.

In Thomson's model, the atom is composed of electrons surrounded by a soup of positive charge to balance the electrons' negative charges, like negatively charged “plums” surrounded by positively charged “pudding”. The 1904 Thomson model was disproved by Hans Geiger's and Ernest Marsden's 1909 gold foil experiment.

Assertion: In Lyman series, the ratio of minimum and maximum wavelength is 3/4
Reason: Lyman series constitute spectral lines corresponding to transition from higher energy to ground state of the hydrogen atom.

Explanation:
The Lyman series is a series of spectral lines in the ultraviolet region of the electromagnetic spectrum that are emitted when electrons in hydrogen atoms transition from higher energy levels to the ground state.

Assertion: In Lyman series, the ratio of minimum and maximum wavelength is 3/4

This statement is correct. The Lyman series consists of a series of spectral lines that correspond to transitions from higher energy levels to the ground state of the hydrogen atom. The wavelengths of these spectral lines can be calculated using the Rydberg formula:

1/λ = R_H * (1/n_1^2 - 1/n_2^2)

where λ is the wavelength, R_H is the Rydberg constant for hydrogen, and n_1 and n_2 are the principal quantum numbers of the initial and final energy levels, respectively.

For the Lyman series, the initial energy level (n_1) is always equal to 1 (the ground state), and the final energy level (n_2) can be any value greater than 1. The minimum wavelength in the Lyman series corresponds to the transition from the first excited state (n_2 = 2) to the ground state (n_1 = 1). The maximum wavelength corresponds to the transition from the highest energy level (n_2 = infinity) to the ground state (n_1 = 1).

The ratio of the minimum and maximum wavelength can be calculated as:

(1/λ_min)/(1/λ_max) = (n_2^2 - n_1^2)/(n_2^2 - 1) = (2^2 - 1^2)/(2^2 - 1) = 3/4

Therefore, the ratio of the minimum and maximum wavelength in the Lyman series is indeed 3/4.

Reason: Lyman series constitute spectral lines corresponding to transition from higher energy to ground state of the hydrogen atom.

This statement is also correct. The Lyman series specifically corresponds to transitions from higher energy levels to the ground state of the hydrogen atom. Each spectral line in the Lyman series represents a specific transition between two energy levels, with the ground state (n=1) being the final energy level for all transitions in this series.

Therefore, both the Assertion and Reason are correct. However, the Reason is not a correct explanation of the Assertion. The Reason simply restates the definition of the Lyman series and does not provide an explanation for why the ratio of minimum and maximum wavelength is 3/4 in this series. The calculation based on the Rydberg formula provides the explanation for this ratio. Hence, the correct answer is option B.

The impact parameter is defined as the perpendicular distance between the path of a projectile and the center of a potential field created by an object that the projectile is approaching. It is often referred to in nuclear physics (see Rutherford scattering) and in classical mechanics.