ATOMS

Question 1

Experiments on electric discharge through gases was carried out by?
What did he reveal?

Answer 1

J J Thomson
Atoms of different elements contain negatively charged constituents also call electrons, Identical for all atoms.

Question 2

First model of atom was proposed by?
What happens according to this model?
This model was picturesquely Called as?
What did subsequent studies on atoms show?

Answer 2

J.J.Thomson
Positive charge of atom uniformly distributed throughout volume of atom and negatively charged electrons embedded like seeds in a watermelon.
Model called Plump Pudding Model of atom.
Show that distribution of Electrons and positive charges very different from the proposed model.

Question 3

Which matter is basically talking about here as condensed matter?
What sort of gas is at all temperatures emit________
The radiation occurs due to?

Answer 3

Solids and liquids
Dense gases Amit electromagnetic radiation where continuous distribution of several wavelengths is present with different intensities

Oscillations of atoms and molecules governed by interaction of each atom or molecule with its neighbours

Question 4

How does this spectrum appear as?

Answer 4

Series of bright lines.

Question 5

Rutherford’s planetary Model of atom was called?
According to this the entire positive charge and most of the mass of the atom is concentrated in ________ Called? With what revolving around the nucleus?

Answer 5

Nuclear model of the atom
A small volume called the nucleus with electrons revolving

Question 6

What was the energy of the alpha-particles directed at the gold foil in the experiment?

Answer 6

The energy of the alpha-particles was 5.5 MeV.

Question 7

Which radioactive source emitted the alpha-particles in the experiment?

Answer 7

The alpha-particles were emitted by a 214_83Bi radioactive source.

Question 8

What was the purpose of using lead bricks in the experiment?

Answer 8

The lead bricks were used to collimate the alpha-particle beam into a narrow beam before it struck the gold foil.

Question 9

What was the thickness of the gold foil used in the experiment?

Answer 9

The thickness of the gold foil was 2.1 × 10^-7 m.

Question 10

How were the scattered alpha-particles detected?

Answer 10

The scattered alpha-particles were detected using a rotatable detector consisting of a zinc sulphide screen and a microscope.

Question 11

What phenomenon occurred when the scattered alpha-particles struck the zinc sulphide screen?

Answer 11

When the scattered alpha-particles struck the zinc sulphide screen, they produced brief light flashes or scintillations.

Question 12

How was the distribution of scattered alpha-particles studied?

Answer 12

The distribution of scattered alpha-particles was studied by observing the number of scattered particles as a function of the angle of scattering using the microscope.

Question 13

What does the solid curve in the graph of alpha-particle scattering represent?

Answer 13

The solid curve represents the theoretical prediction based on the assumption that the target atom has a small, dense, positively charged nucleus.

Question 14

What percentage of alpha-particles scatter by more than 1°?

Answer 14

About 0.14% of the incident alpha-particles scatter by more than 1°.

Question 15

How many alpha-particles deflect by more than 90°?

Answer 15

About 1 in 8000 alpha-particles deflect by more than 90°.

Question 16

What did Rutherford conclude about the force required to deflect alpha-particles backwards?

Answer 16

Rutherford concluded that a large repulsive force was required to deflect alpha-particles backwards, which could only be provided if the greater part of the atom’s mass and positive charge were concentrated in a small, dense nucleus.

Question 17

Why were many alpha-particles able to pass through the foil without any deflection?

Answer 17

Many alpha-particles passed through the foil without deflection because they did not suffer any collisions, meaning they did not encounter the dense nucleus.

Question 18

What key discovery did Rutherford’s experiment lead to?

Answer 18

Rutherford’s experiment led to the discovery of the atomic nucleus, supporting the nuclear model of the atom.

Question 19

According to Rutherford’s nuclear model, where are the entire positive charge and most of the mass of an atom concentrated?

Answer 19

The entire positive charge and most of the mass of an atom are concentrated in the nucleus.

Question 20

How do electrons move in Rutherford’s nuclear model of the atom?

Answer 20

Electrons move in orbits around the nucleus, similar to how planets orbit the Sun.

Question 21

What is the estimated size of the atomic nucleus according to Rutherford’s experiment?

Answer 21

The size of the atomic nucleus is estimated to be 10^-15 m to 10^-14 m.

Question 22

What is the approximate size of an atom as known from kinetic theory?

Answer 22

The approximate size of an atom is 10^-10 m.

Question 23

How much larger is the size of an atom compared to the size of its nucleus?

Answer 23

The size of an atom is about 10,000 to 100,000 times larger than the size of its nucleus.

Question 24

Why is most of the atom considered to be empty space?

Answer 24

Since the electrons are at a distance of about 10,000 to 100,000 times the size of the nucleus, most of the atom consists of empty space.

Question 25

Why do most alpha-particles pass through a thin metal foil without deflection?

Answer 25

Most alpha-particles pass through because the atom is mostly empty space, meaning they do not encounter the nucleus.

Question 26

What happens when an alpha-particle comes near a nucleus?

Answer 26

When an alpha-particle comes near a nucleus, the intense electric field of the nucleus scatters it through a large angle.

Question 27

Why do atomic electrons not significantly affect the motion of alpha-particles?

Answer 27

Atomic electrons are very light compared to alpha-particles, so they do not appreciably affect the alpha-particles' motion.

Question 28

How can the scattering data of alpha-particles be analyzed?

Answer 28

The scattering data can be analyzed using Rutherford’s nuclear model of the atom.

Question 29

Why is it assumed that an alpha-particle suffers at most one scattering in the gold foil?

Answer 29

Since the gold foil is very thin, it is assumed that an alpha-particle will undergo not more than one scattering during its passage.

Question 30

What is the charge and mass of an alpha-particle?

Answer 30

An alpha-particle is the nucleus of a helium atom and carries a charge of +2e. It has the mass of a helium atom.

Question 31

What is the charge of a gold nucleus in terms of elementary charge (e)?

Answer 31

The charge of a gold nucleus is Ze, where Z = 79 for gold. Therefore, the charge is 79e.

Question 32

Why can the gold nucleus be considered stationary during the scattering process?

Answer 32

The gold nucleus is about 50 times heavier than an alpha-particle, making it reasonable to assume that it remains stationary during the scattering process.

Question 33

Which laws are used to compute the trajectory of a scattered alpha-particle?

Answer 33

The trajectory of an alpha-particle is computed using Newton’s second law of motion and Coulomb’s law for electrostatic force.

Question 34

What is the impact parameter in Rutherford scattering?

Answer 34

The impact parameter is the perpendicular distance of the initial velocity vector of the alpha-particle from the center of the nucleus.

Question 35

How does the impact parameter affect the trajectory of an alpha-particle?

Answer 35

A small impact parameter results in large scattering, while a large impact parameter results in small deflection.

Question 36

What happens in a head-on collision between an alpha-particle and the nucleus?

Answer 36

In a head-on collision (minimum impact parameter), the alpha-particle rebounds back with an angle close to 180°.

Question 37

What happens when an alpha-particle has a large impact parameter?

Answer 37

When an alpha-particle has a large impact parameter, it undergoes very little deflection and continues nearly undeviated.

Question 38

What does the small fraction of alpha-particles rebounding back indicate?

Answer 38

It indicates that the number of alpha-particles undergoing head-on collisions is small, meaning the mass and positive charge of the atom are concentrated in a small volume.

Question 39

How does Rutherford scattering help determine the size of the nucleus?

Answer 39

Rutherford scattering provides an upper limit to the size of the nucleus by analyzing how alpha-particles are deflected by the electrostatic field of the nucleus.

Question 40

How does Rutherford's nuclear model describe the atom?

Answer 40

Rutherford's nuclear model describes the atom as an electrically neutral sphere with a small, massive, positively charged nucleus at the center, surrounded by revolving electrons.

Question 41

What force keeps the electrons in their orbits around the nucleus in Rutherford’s model?

Answer 41

The electrostatic force of attraction between the positively charged nucleus and the negatively charged electrons provides the necessary centripetal force to keep the electrons in orbit.

Question 42

What is the equation that describes the balance of forces in a dynamically stable orbit of a hydrogen atom?

Answer 42

Fe = Fc, where Fe is the electrostatic force of attraction, and Fc is the required centripetal force for orbital motion.

Question 43

What assumption does Rutherford's atomic model make about the stability of the atom?

Answer 43

Rutherford's atomic model assumes that the atom, consisting of a central nucleus and revolving electron, is stable, similar to the sun-planet system.

Question 44

What fundamental difference exists between the planetary system and the nucleus-electron system?

Answer 44

The planetary system is held together by gravitational force, whereas the nucleus-electron system interacts through Coulomb’s Law of force due to the charge of the particles.

Question 45

What happens to an object moving in a circular path?

Answer 45

An object moving in a circular path experiences constant acceleration, which is centripetal in nature.

Question 46

What does classical electromagnetic theory state about an accelerating charged particle?

Answer 46

According to classical electromagnetic theory, an accelerating charged particle emits radiation in the form of electromagnetic waves.

Question 47

What should happen to the energy of an accelerating electron, according to classical electromagnetic theory?

Answer 47

The energy of an accelerating electron should continuously decrease as it emits electromagnetic radiation.

Question 48

What would be the consequence of the electron losing energy in Rutherford’s model?

Answer 48

The electron would spiral inward and eventually fall into the nucleus, making the atom unstable.

Question 49

According to classical electromagnetic theory, what is the relationship between the frequency of emitted electromagnetic waves and the motion of electrons?

Answer 49

The frequency of the electromagnetic waves emitted by revolving electrons is equal to their frequency of revolution.

Question 50

What happens to the frequency of emitted radiation as electrons spiral inward?

Answer 50

As electrons spiral inward, their angular velocities change continuously, leading to a continuous change in the frequency of emitted radiation.

Question 51

What contradiction arises between Rutherford’s model and observed atomic spectra?

Answer 51

Rutherford’s model predicts a continuous spectrum, whereas actual atomic spectra are observed as line spectra.

Question 52

What does the failure of Rutherford’s model suggest about classical ideas in atomic structure?

Answer 52

The failure of Rutherford’s model suggests that classical ideas alone are not sufficient to explain atomic structure.

Question 53

Who made modifications to Rutherford’s atomic model by introducing quantum concepts?

Answer 53

Niels Bohr made modifications to Rutherford’s model by incorporating ideas from the developing quantum hypothesis.

Question 54

In which year did Bohr conclude that classical mechanics and electromagnetism were insufficient to explain atomic structure?

Answer 54

In 1913, Bohr concluded that classical mechanics and electromagnetism could not fully explain atomic structure.

Question 55

Why did Bohr believe a radical departure from classical mechanics was necessary?

Answer 55

Bohr realized that classical mechanics and electromagnetism could not explain atomic structure and atomic spectra, requiring new quantum concepts.

Question 56

What was Bohr’s approach to modifying Rutherford’s model?

Answer 56

Bohr combined classical and early quantum concepts to formulate his atomic theory, which included three postulates.

Question 57

What does Bohr’s first postulate state about electron orbits?

Answer 57

Bohr’s first postulate states that an electron can revolve in certain stable orbits without emitting radiation, contradicting classical electromagnetic theory.

Question 58

What are the stable energy states of an atom called?

Answer 58

The stable energy states of an atom are called stationary states.

Question 59

What does the negative sign of an electron’s total energy indicate?

Answer 59

The negative total energy indicates that the electron is bound to the nucleus and requires energy to be removed to an infinite distance.

Question 60

What does Bohr’s second postulate define?

Answer 60

Bohr’s second postulate defines stable orbits where the electron’s angular momentum is quantized as an integral multiple of h/2π.

Question 61

What is the formula for the quantization of angular momentum in Bohr’s model?

Answer 61

The angular momentum (L) is given by L = nh/2π, where n is an integer and h is Planck’s constant.

Question 62

What fundamental quantum concepts did Bohr’s third postulate incorporate?

Answer 62

Bohr’s third postulate incorporated Planck’s and Einstein’s quantum concepts, stating that electrons transition between energy levels by emitting or absorbing photons.

Question 63

What happens when an electron transitions from a higher energy level to a lower one?

Answer 63

When an electron transitions to a lower energy level, it emits a photon with energy equal to the difference between the initial and final states.

Question 64

What equation determines the frequency of the emitted photon in Bohr’s model?

Answer 64

The frequency of the emitted photon is given by hn = Ei – Ef, where Ei and Ef are the energies of the initial and final states, respectively.

Question 65

What condition is required to determine the energy levels of a hydrogen atom?

Answer 65

The equation for energy levels requires the radius of the electron orbit, which is calculated using Bohr’s second postulate on angular momentum quantization.