← Back to chapter
Vidaara.orgClass 11 · Chemistry
CodeVID-C11-02-CH-01
Structure of Atom — Full Chapter Assignment
Chapter: Structure of Atom
Topic: All Topics
Maximum Marks: 40
Time: 90 minutes
Name: ____________________ Roll No.: __________ Date: ____________

General Instructions

  • All questions are compulsory.
  • Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
  • Use $h=6.626\times10^{-34}\,\text{J s}$, $R_H=1.097\times10^{7}\,\text{m}^{-1}$, $m_e=9.11\times10^{-31}\,\text{kg}$ where required.
  • Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions 6 × 1 = 6 marks
1.
The mass of a proton is about how many times that of an electron?
  • A.18
  • B.183
  • C.1837
  • D.9.11
2.
Neutrons in $^{31}_{15}\text{P}$:
  • A.15
  • B.16
  • C.31
  • D.46
3.
Energy of the $n=2$ level of hydrogen:
  • A.$-13.6\,\text{eV}$
  • B.$-3.40\,\text{eV}$
  • C.$-1.51\,\text{eV}$
  • D.$0$
4.
The Paschen series lies in the:
  • A.UV region
  • B.visible region
  • C.infrared region
  • D.X-ray region
5.
The number of orbitals in a $p$ sub-shell:
  • A.1
  • B.3
  • C.5
  • D.7
6.
The configuration $[\text{Ar}]\,3d^{10}\,4s^1$ is that of:
  • A.Cr
  • B.Mn
  • C.Cu
  • D.Zn
Section B — Short Answer (2 marks) 4 × 2 = 8 marks
7.
Define atomic number and mass number, and give the relation for the number of neutrons.
8.
State two limitations of Bohr's model of the atom.
9.
Write the electronic configuration of $\text{O}^{2-}$ ($Z$ of O $=8$).
10.
How many unpaired electrons are present in a ground-state nitrogen atom? Justify using Hund's rule.
Section C — Short Answer (3 marks) 2 × 3 = 6 marks
11.
Calculate the wavelength of the $\text{H}_\alpha$ line of the Balmer series ($n_2=3\to n_1=2$), $R_H=1.097\times10^{7}\,\text{m}^{-1}$.
12.
Calculate the de Broglie wavelength of an electron accelerated so that it moves at $5.0\times10^{6}\,\text{m s}^{-1}$.
Section D — Long Answer (5 marks) 2 × 5 = 10 marks
13.
Explain the four quantum numbers with their permissible values and use them to write the complete set for the valence electron of potassium ($Z=19$).
14.
State the Aufbau principle, Pauli principle and Hund's rule, and use them with the half-filled-stability idea to explain the configuration of chromium ($Z=24$). How many unpaired electrons does it have?

Answer Key

Section A — Multiple Choice Questions
  1. (C) 1837
  2. (B) 16
  3. (B) $-3.40\,\text{eV}$
  4. (C) infrared region
  5. (B) 3
  6. (C) Cu
Section B — Short Answer (2 marks)
  1. $Z$ = number of protons; $A$ = protons + neutrons; neutrons $=A-Z$.
  2. Works only for one-electron species; cannot explain fine structure / Zeeman-Stark splitting; ignores wave nature and uncertainty principle (any two).
  3. O is $1s^2\,2s^2\,2p^4$; add 2 electrons: $\text{O}^{2-}=1s^2\,2s^2\,2p^6$ (= [Ne]).
  4. Three: $2p^3$ fills $p_x,p_y,p_z$ singly with parallel spins (Hund's rule), so all three are unpaired.
Section C — Short Answer (3 marks)
  1. $1/\lambda=R_H(1/4-1/9)=R_H\times5/36=1.524\times10^{6}\,\text{m}^{-1}$; $\lambda\approx656\,\text{nm}$.
  2. $\lambda=h/mv=6.626\times10^{-34}/(9.11\times10^{-31}\times5.0\times10^{6})=1.46\times10^{-10}\,\text{m}$.
Section D — Long Answer (5 marks)
  1. $n$ (shell), $l$ (0 to $n-1$, shape), $m_l$ ($-l$ to $+l$), $m_s$ ($\pm\tfrac{1}{2}$). K = $[\text{Ar}]\,4s^1$; valence electron: $n=4,l=0,m_l=0,m_s=+\tfrac{1}{2}$.
  2. Rules as stated. Expected $3d^4\,4s^2$ but actual $[\text{Ar}]\,3d^5\,4s^1$ because a half-filled $3d^5$ is extra stable (high exchange energy). Unpaired electrons = 6 ($3d^5$ + $4s^1$).
Generated by Vidaara.org · Assignment VID-C11-02-CH-01 · vidaara.org