# Atomic Structure Terminal Questions with Answer NIOS

### National Institute of Open Schooling (NIOS)

Sr. Secondary, Module-1

Lession-2: Atomic Structure Terminal Questions with Answer

## Terminal QUESTIONS with Answer

### 1. a. What are the three fundamental particles that constitute an atom?

b. Complare the charge and mass of an electron and of a proton.

Answer:a. Following are the constitute particles that forms an atom-

Electron(e), Proton(p) and Neutron(n).

b.

Particles | Relative Mass | Relative Charge | Absolute Mass | Absolute Charge |
---|---|---|---|---|

Electron | 0.0005 | -1 | 9.11x10^{-31} | -1.6x10^{-19} |

Proton | 1 | +1 | 1.67x10^{27} | +1.6x10^{-19} |

Neutron | 1 | Neutral | 1.67x10^{27} | 0 |

### 2. What do you think is the most significant contribution of Rutherford to the development of atomic structure?

Answer:The most significant contribution to the development of atomic structure is giving the idea of atomic nucleus which is a dense and positively charged region located at the centre of atom.

### 3. What experimental evidence shows the dual nature of light?

Answer:From Young's double-slit interference experiment, the dual behavior of light can be established.

Optical phenomena like reflection, refraction, diffraction regarded light as wave. However, in order to explain the photoelectric effect, Einstein regarded light as tiny particles called photons.

### 4. In what way was the Bohr's model better than Rutherford's model?

Answer:The advantages of the Bohr atomic model over the Rutherford model are given below-

1. Explanation of Atomic Spectra:

The Rutherford model failed to explain the observed atomic spectra, where atoms emit or absorb light at specific wavelengths. However, the Bohr model successfully explained the discrete atomic spectra by proposing that electrons in an atom occupy specific energy levels or orbits.

According to Bohr, when an electron transitions from a higher energy level to a lower one, it emits energy in the form of light. The emitted light corresponds to a specific wavelength, thus explaining the atomic spectra.

2. Stability of Atoms:

Rutherford's model depicted electrons orbiting the nucleus in a manner similar to planets orbiting the Sun. However, according to classical electromagnetic theory, accelerating charged particles emit radiation and lose energy. Consequently, the electrons would spiral into the nucleus, causing atoms to be unstable. Bohr addressed this issue by proposing that electrons can only exist in specific energy levels or orbits. These orbits have fixed energies and do not emit radiation. This concept of quantized energy levels provided stability to the atom.

3. Explanation of Line Spectra:

The Rutherford model could not explain why elements emit light at specific wavelengths, resulting in line spectra. In the Bohr model, the electrons can only occupy certain energy levels, and when they transition between these levels, they emit or absorb energy in the form of photons with specific wavelengths. This explanation accounted for the observed line spectra of elements and provided a better understanding of their atomic structure.

4. Quantization of Angular Momentum:

Rutherford's model did not account for the quantization of angular momentum in the atom. Bohr's model introduced the concept of quantized angular momentum, stating that the angular momentum of an electron is quantized and can only take certain discrete values. This concept explained various experimental observations and was consistent with the quantized energy levels proposed by Bohr.

5. Predictive Power:

The Bohr model's ability to explain atomic spectra and the stability of atoms led to its success in predicting the behavior of atoms in various situations. It provided a framework for understanding the behavior of electrons in atoms and laid the foundation for further advancements in atomic theory.

In conclusion, the Bohr atomic model overcame several limitations of the Rutherford model by explaining atomic spectra, providing stability to atoms, explaining line spectra, introducing the concept of quantized angular momentum, and demonstrating strong predictive power. These advantages made the Bohr model a significant advancement in our understanding of atomic structure.

### 5. What are the drawbacks of Bohr's Model?

Answer:The drawbacks of Bohr's Model are given blow-

It fails to explain

The spectra of multi-electron atoms.

The movement of electrons in three-dimensional space called orbital around the nucleus and not in planar orbits.

The reason of chemical combinations and the formation of new molecules out of it.

Heisenberg's uncertainty principle which suggests that it is impossible to measure the exact position and momentum of particles like electrons simultaneously. (As according to Bohr's model assumes a definite knowledge about the exact position and momentum simultaneously.)

Relative intensity of spectral lines

Zeeman Effect: splitting of spectral lines on the application of magnetic field.

### 6. What led to the development of wave mechanical model of the atom ?

Answer:The development of Wave Mechanism Model is as under

It is a mechanical function that describes the motion of an electron inside the atom. It contains all the information about the system and can be found by solving of Schrodinger wave equation.

The quantum numbers are integers that characterize the wave functions. These are obtained in the process of solving Schrodinger wave equation and every electron in an atom has a different set of quantum numbers. The three quantum numbers obtained from Schrodinger wave equation are a. The principal quantum number(n)

b. (ii) Azimuthal quantum number(I)

c. The magnetic quantum number(m)

The principal quantum number 'n' is concerned with the energy of the electron in a shell. The quantum number 'l' is related to the geometrical shape of the orbital and the quantum number 'm' describes the orientation of the orbital in space.

### 7. What do you understand by an orbital? Draw the shapes of s and p orbitals.

Answer:Orbitals are mathematical functions that determine regions around the atom that has the highest probability to find an atom .Subsequently they also refer to the physical boundaries of space derived from such functions where the probability of an electron existing is highest.

From the figures, we can see that the s orbital is spherical and for the p orbitals a dumbbell. Because of their shapes, s orbitals have only a single orientation while p orbitals have three (x,y,z) which can hold two electrons respectively.

### 8. Explain the Hund's rule of maximum multiplicity with the help of an example.

Answer:Friedrich Hund in 1925, states that the greatest value of spin multiplicity has the lowest energy term. So, electron pairing in orbitals belonging to the same subshell (p, d, or f) does not occur until each orbital of that subshell has one electron, i.e. it is singly occupied. After singly occupied, pairation takes place with opposite spin.

hund’s rule of maximum multiplicity is used to determine the electronic configuration of elements.

Let's consider the filling of 2p orbitals. There are three degenerate(same energy) orbitals in every p subshell. The first electron enters either of three orbitals since they are degenerate. Even though the first-occupied orbital is not completely filled and it can take one more electron, the second electron will not occupy it. Instead, it will enter another orbital with the same spin as the first electron. Similarly, the third will occupy the remaining orbital. Thus, the first three electrons occupy all three orbitals (p

_{x}, p

_{y}, p

_{z}) with either spin up or spin down. After singly filling, the 4th, 5th and 6th electrons(↑ in figure) will fill the remaining empty orbitals, which results in pairing.

Similarly, we can understand the filling of d and f orbitals.