100 Short Q&A for Atomic Structure (Class 11 NCERT)

100 Short Q&A for Atomic Structure (Class 11 NCERT)

Part 1: Fundamental Particles and Early Models

Q. No.	Question	Answer
1	Who discovered the electron?	J. J. Thomson (using Cathode Ray Tube).
2	Who discovered the proton?	E. Goldstein (using Canal Rays).
3	Who discovered the neutron?	James Chadwick.
4	What is the charge-to-mass ratio (e/m) of an electron?	1.758820×1011 C/kg.
5	What is the charge of an electron?	−1.602×10−19 Coulombs (Millikan's Oil Drop method).
6	What is the mass of a proton (in kg)?	Approximately 1.672×10−27 kg.
7	What is an α-particle?	A doubly positively charged helium nucleus (4He2+).
8	What did Thomson's model of the atom propose?	A "Plum Pudding" or "Watermelon" model with embedded electrons.
9	What was the major observation of Rutherford's α-scattering experiment?	Most α-particles passed straight through the gold foil.
10	What is the dense, central part of an atom called?	The Nucleus.
11	What did Rutherford's model fail to explain?	The stability of the atom.
12	Define Atomic Number (Z).	The number of protons in the nucleus.
13	Define Mass Number (A).	The total number of protons and neutrons (nucleons).
14	What are Isotopes?	Atoms of the same element with the same Z but different A (different neutrons).
15	What are Isobars?	Atoms with the same A but different Z (different elements).
16	What are Isotones?	Atoms with the same number of neutrons.
17	What are isoelectronic species?	Species (atoms/ions) having the same number of electrons.
18	Write the symbol for an element X with Z=17 and A=35.	1735​Cl (Chlorine).
19	How many neutrons are in a 235U atom?	235−92=143 neutrons.
20	Who proposed that energy is quantized?	Max Planck.

Part 2: Dual Nature of Matter and Electromagnetic Radiation

 

Q. No.	Question	Answer
21	What is the velocity of electromagnetic radiation in a vacuum?	The speed of light (c), approximately 3.0×108 m/s.
22	What is the relationship between frequency (ν) and wavelength (λ)?	c=νλ.
23	Which region of the electromagnetic spectrum has the highest frequency?	Gamma Rays.
24	What is the SI unit of frequency?	Hertz (Hz) or s−1.
25	What is the energy of one photon given by (Planck's Equation)?	E=hν (where h is Planck's constant).
26	What is the value of Planck's constant (h)?	6.626×10−34 J s.
27	What is a Black Body?	An ideal body that absorbs and emits all frequencies of radiation equally.
28	What is the Photoelectric Effect?	The ejection of electrons when light of sufficient frequency strikes a metal surface.
29	What is Threshold Frequency (ν0​)?	The minimum frequency of light required to cause the photoelectric effect.
30	What are the two aspects of the Dual Nature of Electromagnetic Radiation?	Wave nature and Particle nature.
31	What is a spectrum?	The display of components of an electromagnetic radiation arranged according to frequency or wavelength.
32	What is an emission spectrum?	The spectrum of radiation emitted by a substance that has absorbed energy.
33	What is a line spectrum?	A spectrum consisting of sharp, well-defined lines (characteristic of atoms).
34	What type of spectrum is the hydrogen spectrum?	A line emission spectrum.
35	Which series in the hydrogen spectrum lies in the UV region?	The Lyman series.
36	Which series in the hydrogen spectrum lies in the visible region?	The Balmer series.
37	State the de Broglie hypothesis.	Matter, like radiation, exhibits dual behavior (wave and particle).
38	Write the de Broglie wavelength equation.	λ=h/(mv) (where p=mv is momentum).
39	Which particle shows wave properties even at ordinary speeds?	Microscopic particles like electrons.
40	What is the energy of the electron in the n=1 state of a hydrogen atom?	−2.18×10−18 J or −13.6 eV.

Part 3: Bohr's Model and Quantum Mechanical Model

 

Q. No.	Question	Answer
41	What is the main postulate of Bohr's model regarding electron orbits?	Electrons revolve only in certain fixed, non-radiating orbits (stationary states).
42	What is the condition for the angular momentum of an electron in Bohr's model?	It must be an integral multiple of h/(2π), i.e., mvr=n⋅h/(2π).
43	What happens when an electron jumps from a lower to a higher orbit?	Energy is absorbed.
44	What happens when an electron drops from a higher to a lower orbit?	Energy is emitted (as a photon).
45	Give the Rydberg formula for the wavelength of hydrogen spectral lines.	1/λ=RH​(n12​1​−n22​1​).
46	What is the value of the Rydberg constant (RH​)?	109677 cm−1.
47	What is the main limitation of Bohr's model?	It could not explain the spectra of multi-electron atoms.
48	What is the Heisenberg Uncertainty Principle?	It is impossible to determine simultaneously and exactly the position and momentum of a microscopic particle.
49	Write the mathematical expression for the Uncertainty Principle.	Δx⋅Δp≥h/(4π).
50	What is the region of space around the nucleus where the probability of finding an electron is maximum?	An Orbital.
51	What are the three Quantum Numbers derived from the Schrödinger Wave Equation?	Principal (n), Azimuthal (l), and Magnetic (ml​).
52	What does the Principal Quantum Number (n) determine?	The size and energy of the orbit/shell.
53	What are the possible values of n?	1,2,3,4,… (or K,L,M,N,…).
54	What does the Azimuthal (or Angular Momentum) Quantum Number (l) determine?	The shape of the orbital (subshell).
55	What are the possible values of l for a given n?	0 to (n−1).
56	What are the subshells corresponding to l=0,1,2,3?	s,p,d,f.
57	What does the Magnetic Quantum Number (ml​) determine?	The orientation of the orbital in space.
58	What are the possible values of ml​ for a given l?	−l to +l (including 0).
59	How many orbitals are in the d-subshell (l=2)?	Five (ml​=−2,−1,0,+1,+2).
60	What does the Spin Quantum Number (ms​) determine?	The orientation of the electron's spin.
61	What are the two possible values of ms​?	+1/2 (spin up) and −1/2 (spin down).
62	What is the shape of an s orbital?	Spherical.
63	What is the shape of a p orbital?	Dumb-bell shaped.
64	How many nodal planes does a p orbital have?	One (a plane passing through the nucleus).
65	Define a Radial Node.	A spherical surface where the probability of finding the electron is zero.
66	What is the formula for the total number of nodes?	n−1.
67	What is the formula for the number of angular nodes?	l.
68	What is the formula for the number of radial nodes?	n−l−1.
69	What is the total number of nodes for a 3p orbital?	3−1=2 (1 radial, 1 angular).
70	How many degenerate orbitals are present in the M-shell (n=3)?	32=9 (one 3s, three 3p, five 3d).

Part 4: Electronic Configuration Rules

 

Q. No.	Question	Answer
71	State the Aufbau Principle.	Electrons are added one by one to orbitals with the lowest energy first.
72	What is the (n+l) rule used for?	To determine the relative energy of orbitals.
73	Which orbital has lower energy: 4s or 3d?	4s (n+l is 4+0=4, vs 3+2=5).
74	State Pauli's Exclusion Principle.	No two electrons in an atom can have the same set of all four quantum numbers.
75	What is the maximum number of electrons in an orbital?	Two (with opposite spins).
76	State Hund's Rule of Maximum Multiplicity.	Pairing of electrons in a degenerate set of orbitals (p,d,f) does not occur until each orbital has one electron (singly occupied).
77	Write the electronic configuration of Nitrogen (Z=7).	1s22s22p3.
78	What is the total number of unpaired electrons in Oxygen (Z=8)?	Two (↑↓ in 2s, ↑↓↑↑ in 2p).
79	Why is the electronic configuration of Chromium (Z=24) exceptional?	Half-filled orbitals are more stable, so it is [Ar]3d54s1 instead of 3d44s2.
80	Why is the electronic configuration of Copper (Z=29) exceptional?	Fully-filled orbitals are more stable, so it is [Ar]3d104s1 instead of 3d94s2.
81	Write the electronic configuration of Na+ ion (Z=11).	1s22s22p6 (Neon configuration).
82	How many orbitals are singly occupied in the ground state of Chlorine (Z=17)?	One (3p orbital).
83	What is the order of filling of electrons in the 5th period according to the (n+l) rule?	5s,4d,5p (then 6s,4f,…).
84	What is the general electronic configuration for the p-block elements?	ns2np1−6.
85	What is the highest value of n for an electron in the ground state of Potassium (Z=19)?	n=4 (4s1).
86	What is the maximum number of electrons in the n=4 shell?	2n2=2(42)=32 electrons.
87	How is the energy of orbitals determined in multi-electron atoms?	By the (n+l) rule (and n if (n+l) is equal).
88	What is the minimum energy required to remove an electron from the ground state of an atom?	Ionization Enthalpy (or Ionization Energy).
89	What is the magnetic behavior of a species with unpaired electrons?	Paramagnetic.
90	What is the magnetic behavior of a species with all paired electrons?	Diamagnetic.
91	Is N2​ (Nitrogen molecule) paramagnetic or diamagnetic?	Diamagnetic (all electrons are paired).
92	What is a Wave Function (ψ)?	A mathematical function that contains all the information about an electron in an atom.
93	What does ψ2 represent?	The probability density of finding the electron at a point.
94	Which quantum number is not obtained from the Schrödinger equation?	The Spin Quantum Number (ms​).
95	What is the relationship between the radius of the n-th orbit and n in Bohr's model?	rn​∝n2 (for H-like species).
96	Define Atomic Mass Unit (amu) or u.	1/12 of the mass of a C−12 atom.
97	What is the term for the stability gained by half-filled and fully-filled subshells?	Exchange Energy (or greater symmetry).
98	In a hydrogen atom, what determines the energy of an electron?	Only the Principal Quantum Number (n).
99	What is the frequency of light when an electron jumps from n=3 to n=2 in a H-atom?	The first line of the Balmer series (Red light).
100	What are the main characteristics of a cathode ray?	They are streams of electrons; travel in straight lines; and are deflected by electric and magnetic fields.