This set of Physical Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Angular Momentum of Many-Electron Atoms”.
1. What does the Pauli Exclusion Principle state?
a) Electrons in a single atom must have unique quantum numbers
b) Electrons in a single atom cannot have unique quantum numbers
c) Electrons in a single atom may have non-unique quantum numbers
d) Electrons in a single atom do not have quantum numbers
View Answer
Explanation: The Pauli Exclusion Principle states that electrons in a single atom or molecule must have unique quantum numbers. This arises because of fermions. Possible values for quantum numbers:
Principal quantum number, n=1, 2, 3…
Angular quantum number, l= 0, 1, 2…n-1
Magnetic quantum number, ml = -l, …, -1, 0, 1, …, l
Spin quantum number, ms = +1/2, -1/2
2. What is the electronic configuration of helium atom at its ground state?
a) 2s2
b) 1s2
c) 2s2 2p6
d) 2p6
View Answer
Explanation: Helium has only two electrons and therefore its electronic configuration at the ground state will be 1s2. Because first orbital is full with 2 electrons, and any additional electrons would go in a new energy level.
3. Why Neon is known as noble gas?
a) Its p subshell is incomplete
b) Its electronic configuration is 2s22p5
c) Its s subshell is incomplete
d) Its electronic configuration is 2s22p6
View Answer
Explanation: Neon has an electronic configuration of 2s22p6, which states that it possesses inert gas electron configuration that means the subshell p of Neon is completely filled, and therefore, Neon is also known as noble or inert gas.
4. Which formula is correct for total angular momentum?
a) \(\vec{J} = \vec{L} + \vec{S}\)
b) \(\vec{J}\)= 0
c) \(\vec{L} = \vec{J} + \vec{S}\)
d) \(\vec{S} = \vec{L} + \vec{J}\)
View Answer
Explanation: Total angular momentum is the sum of the orbital angular momentum and spin angular momentum. It is given by the formula,
\(\vec{J} = \vec{L} + \vec{S}\) is the orbital angular momentum and \(\vec{S}\) is spin angular momentum.
5. Which of the following is an alkali?
a) Neon
b) Chlorine
c) Sodium
d) Helium
View Answer
Explanation: Neon (2s22p6) and Helium (2s2) both have inert gas electron configuration, thus, both are inert gases. Chlorine (3s23p5) has one electron short of a closed shell, thus, chlorine is a halogen. Sodium (3s1) a single electron outside the closed shell, therefore, sodium is an alkali.
6. Which of the following is a halogen?
a) 2s22p6
b) 3s1
c) 3s23p5
d) 2s2
View Answer
Explanation: 2s2 and 2s22p6 have completely filled s and p subshells respectively, so both are inert gases. 3s1 has single atom outside the closed p shell, thus it is an alkali. 3s23p5 has one electron short of a closed shell, and therefore it is a halogen.
7. What is the electronic configuration of Boron at its ground state?
a) 1s2
b) 1s22s22p1
c) 2s2
d) 2s22p6
View Answer
Explanation: Boron is the fifth element with a total of five electrons, so in ground state, the first two electrons will go in the 1s orbital, next two electrons will go in 2s orbital and remaining one electron will go in p subshell. Thus, the electronic configuration of Boron at its ground state will be 1s22s22p1.
8. What is meant by excited state?
a) Same as ground state
b) Movement of electron to lowest energy orbital
c) Movement of electron from lowest to highest energy orbital
d) No movement of electron
View Answer
Explanation: An excited state means that state when the valence electron moves from its ground state orbital or lowest available energy orbital to other higher state orbital or higher available energy orbital. When valence electron is in higher energy orbital, it is said to be in an excited state.
9. Does electronic configuration affect the properties and trends of any element or compound?
a) True
b) False
View Answer
Explanation: Electronic configuration decides the number of bonds that an atom can form to other atoms, which may result in the changing of physical, chemical, spectroscopic and magnetic properties of any element or compound.
10. Which of the following statements are true?
Statement 1: Electronic configuration of sodium is 1s22s22p63s1.
Statement 2: Electronic configuration of sodium ion is 1s22s22p6.
a) Statement 1 is true but statement 2 is false
b) Statement 2 is true but statement 1 is false
c) Statement 1 and statement 2, both are true
d) Statement 1 and statement 2, both are false
View Answer
Explanation: The electronic configuration of neutral sodium atom is 1s22s22p63s1, where one electron is more than the closed p subshell so, sodium gives up the valence electron and therefore the electron configuration of sodium ion is 1s22s22p6, giving Na a positive charge and it becomes Na+.
Sanfoundry Global Education & Learning Series – Physical Chemistry.
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