In Class 11 Final Exams there will be Case studies and Passage Based Questions will be asked, So practice these types of questions. Study Rate is always there to help you. Free PDF Downloads of CBSE Class 11 Chemistry Chapter 2 Case Study and Passage-Based Questions with Answers were Prepared Based on the Latest Exam Pattern. Students can solve Class 11 Chemistry Case Study Questions Structure of Atom to know their preparation level.

In CBSE Class 11 Chemistry Paper, There will be a few questions based on case studies and passage-based as well. In that, a paragraph will be given, and then the MCQ questions based on it will be asked.

Structure of Atom Case Study Questions With Answers

Here, we have provided case-based/passage-based questions for Class 11 Chemistry Chapter 2 Structure of Atom

Case Study/Passage-Based Questions

Case Study 1: The French physicist, de Broglie, in 1924 proposed that matter, like radiation, should also exhibit dual behaviour i.e., both particle and wavelike properties. This means that just as the photon has momentum as well as wavelength, electrons should also have momentum as well as wavelength, de Broglie, from this analogy, gave the following relation between wavelength (λ) and momentum (p) of material particle

where m is the mass of the particle, v its velocity and p is its momentum.

Werner Heisenberg a German physicist in 1927, stated the uncertainty principle which is the consequence of the dual behaviour of matter and radiation. It states that it is impossible to determine simultaneously, the exact position and exact momentum (or velocity)of an electron. Mathematically, it can be given as in equation

where ∆x is the uncertainty in position and ∆p_x(or ∆v_x) is the uncertainty in momentum (or velocity) of the particle.

One of the important implications of the Heisenberg Uncertainty Principle is that it rules out the existence of definite paths or trajectories of electrons and other similar particles. The effect of the Heisenberg Uncertainty Principle is significant only for the motion of microscopic objects and is negligible for that of macroscopic objects. It, therefore, means that the precise statements of the position and momentum of electrons have to be replaced by the statements of probability, that the electron has at a given position and momentum. This is what happens in the quantum mechanical model of the atom. In the Bohr model, an electron is regarded as a charged particle moving in well-defined circular orbits about the nucleus. The wave character of the electron is not considered in the Bohr model. Further, an orbit is a clearly defined path and this path can completely be defined only if both the position and the velocity of the electron are known exactly at the same time. This is not possible according to the Heisenberg uncertainty principle. Bohr’s model of the hydrogen atom, therefore, not only ignores the dual behaviour of matter but also contradicts Heisenberg’s uncertainty principle. The structure of the atom was needed which could account for the wave-particle duality of matter and be consistent with Heisenberg’s uncertainty Principle. This came with the advent of Quantum mechanics. This is mainly because of the fact that classical mechanics ignores the concept of dual behaviour of matter especially for sub-atomic particles and the uncertain principle. The branch of science that takes into account this dual behaviour of matter is called quantum mechanics. Quantum mechanics is a theoretical science that deals with the study of the motions of microscopic objects that have both observable wave-like and particle-like properties. When the Schrödinger equation is solved for the hydrogen atom, the solution gives the possible energy levels the electron can occupy and the corresponding wave function(s) (ψ) of the electron associated with each energy level. A large number of orbitals are possible in an atom. Qualitatively these orbitals can be distinguished by their size, shape and orientation. An orbital of smaller size means there is more chance of finding the electron near the nucleus. Similarly, shape and orientation mean that there is more probability of finding the electron along certain directions than along others. Atomic orbitals are precisely distinguished by what are known as quantum numbers. Each orbital is designated by three quantum numbers labelled as n, l and m_1.

The principal quantum number ‘n’ is a positive integer with a value of n = 1,2,3…….The principal quantum number determines the size and to a large extent the energy of the orbital. Azimuthal quantum number. ‘l’ is also known as orbital angular momentum or subsidiary quantum number. It defines the three-dimensional shape of the orbital. For a given value of n, l can have n values ranging from 0 to n – 1, that is, for a given value of n, the possible value of l are l = 0, 1, 2, ……….(n–1)

Magnetic orbital quantum number. ‘gives information about the spatial orientation of the orbital with respect to a standard set of coordinate axis. For any sub-shell (defined by ‘l’ value) 2l+1 values of ml are possible and these values are given buy: ml = – l, – (l –1), – (l–2)… 0,1… (l –2), (l–1)..

In 1925, George Uhlenbeck and SamuelGoudsmit proposed the presence of the fourth quantum number known as the electron-spin quantum number (ms). electron has, besides charge and mass, intrinsic spin angular quantum number. The spin angular momentum of the electron — a vector quantity, can have two orientations relative to the chosen axis. These two orientations are distinguished by the spin quantum numbers which can take the values of +½ or –½. These are called the two spin states of the electron and are normally represented by two arrows, ↑ (spin up) and ↓ (spin down). the four quantum numbers provide the following information :

i) n defines the shell, determines the size of the orbital and also to a large extent the energy of the orbital.

ii) There are n subshells in the n shell. Identifies the subshell and determines the shape of the orbital (see section 2.6.2). There are (2l+1) orbitals of each type in a subshell, that is, one s orbital (l = 0), three orbitals (l = 1) and five d orbitals (l = 2)per subshell. To some extent, l also determines the energy of the orbital in a multi-electron atom.

iii) ml designates the orientation of the orbital. A given value of l, has (2l+1) values, the same as the number of orbitals per-subshell. It means that the number of orbitals is equal to the number of ways in which they are oriented.

iv) ms refers to the orientation of the spin of the electron.

1) Uncertainty principle was given by.

• (a) Werner Heisenberg
• (b) George Uhlenbeck
• (c) Samuel Goudsmit
• (d) De Broglie

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2) Quantum mechanics is a theoretical science that deals with the study of the motions of the ….. objects.

• (a) Macroscopic
• (b) Microscopic
• (c) Laparoscopic
• (d) All the above

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3)   The principal quantum number …

• (a) l
• (b) m
• (c) n
• (d) p

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4) …is also known as orbital angular momentum or subsidiary quantum number.

• (a) principal quantum number
• (b) electron spin quantum number
• (c) Magnetic orbital quantum number.
• (d) Azimuthal quantum number

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5) George Uhlenbeck and Samuel Goudsmit proposed the presence of the fourth quantum number known as the …

• (a) principal quantum number
• (b) electron spin quantum number
• (c) Magnetic orbital quantum number.
• (d) Azimuthal quantum number

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What is the significance of Heisenberg’s Uncertainty Principle?
A) It predicts the exact position and momentum of an electron.
B) It rules out definite paths of electrons and leads to probability statements.
C) It supports Bohr’s model of the hydrogen atom.
D) It describes the structure of the nucleus.

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Which quantum number defines the shape of an orbital?
A) Principal Quantum Number (n)
B) Azimuthal Quantum Number (l)
C) Magnetic Quantum Number (m₁)
D) Spin Quantum Number (mₛ)

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Why did the Bohr model fail to describe the structure of atoms?
A) It ignored the gravitational force.
B) It contradicted the Heisenberg Uncertainty Principle.
C) It focused only on atomic nuclei.
D) It only described non-hydrogen atoms.

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