Short Q&A for Chemical Bonding and Molecular Structure (Class 11 NCERT)

 

Over 110 Short Q&A for Chemical Bonding and Molecular Structure (Class 11 NCERT)

Part 1: Basic Concepts and Valence Bond Theory (VBT)

Q. No.	Question	Answer
1	What is a Chemical Bond?	The attractive force that holds various constituents (atoms, ions) together in different chemical species.
2	Why do atoms combine to form molecules?	To acquire a stable configuration (usually octet or duplet).
3	State the Octet Rule.	Atoms tend to achieve eight electrons in their valence shell.
4	Give one example of a molecule that violates the Octet Rule (incomplete octet).	BCl3​ or LiCl.
5	Give one example of a molecule that violates the Octet Rule (expanded octet).	SF6​ or PCl5​.
6	Who proposed the concept of electrovalent (ionic) and covalent bonds?	Kossel and Lewis.
7	What is an Ionic Bond?	The electrostatic force of attraction between two oppositely charged ions formed by complete transfer of electrons.
8	What is a Covalent Bond?	A bond formed by the mutual sharing of electrons between two atoms.
9	What are Lewis Dots Structures?	Diagrams showing valence electrons as dots around the atomic symbol.
10	Define Bond Enthalpy.	The energy required to break one mole of a particular type of bond in the gaseous state.
11	Define Bond Length.	The equilibrium distance between the nuclei of two bonded atoms in a molecule.
12	What is the relationship between bond order and bond length?	Higher the bond order, shorter the bond length.
13	What is a Coordinate Bond (or Dative Bond)?	A bond where both shared electrons are contributed by one atom only.
14	What is Lattice Enthalpy?	The energy required to completely separate one mole of a solid ionic compound into gaseous constituent ions.
15	What is the driving force for the formation of an ionic bond?	High Lattice Enthalpy and low Ionization Enthalpy/high Electron Gain Enthalpy.
16	Which type of bond is directional?	Covalent bond.
17	Which type of bond is non-directional?	Ionic bond.
18	What is the principle of Valence Bond Theory (VBT)?	Covalent bond formation occurs via the overlapping of atomic orbitals.
19	What is a σ (sigma) bond?	A bond formed by head-on (axial) overlap of orbitals.
20	What is a π (pi) bond?	A bond formed by sideways (lateral) overlap of orbitals.
21	Which is stronger, a σ bond or a π bond?	σ bond (due to greater extent of overlap).
22	What kind of bond is the first bond formed between two atoms?	Always a σ bond.
23	How many σ and π bonds are in N2​ molecule?	One σ and two π bonds (a triple bond).

Part 2: VSEPR Theory and Molecular Geometry

Q. No.	Question	Answer
24	What does VSEPR stand for?	Valence Shell Electron Pair Repulsion Theory.
25	What is the main postulate of VSEPR theory?	Electron pairs (both lone and bond pairs) repel each other and arrange themselves to minimize repulsion.
26	Rank the repulsion order: lp-lp,lp-bp,bp-bp.	lp-lp>lp-bp>bp-bp (Lone pair-Lone pair is highest).
27	What is the geometry of a molecule with two bond pairs and zero lone pairs (AB2​)?	Linear (180∘).
28	What is the geometry of BF3​?	Trigonal Planar (120∘).
29	What is the geometry of CH4​?	Tetrahedral (109.5∘).
30	What is the geometry of PCl5​?	Trigonal Bipyramidal.
31	What is the geometry of SF6​?	Octahedral.
32	What is the shape of NH3​?	Trigonal Pyramidal (due to one lone pair).
33	What is the bond angle in NH3​?	107∘ (less than 109.5∘ due to lp-bp repulsion).
34	What is the shape of H2​O?	Bent or V-shape (due to two lone pairs).
35	What is the bond angle in H2​O?	104.5∘ (less than 109.5∘ due to two lp-bp repulsions).
36	What is the geometry of XeF4​?	Square Planar (six pairs, two lone pairs on axial positions).
37	What is the hybridization and shape of IF5​?	sp3d2, Square Pyramidal.
38	What is the hybridization and shape of I3−​ ion?	sp3d, Linear (three lone pairs on equatorial positions).
39	What is the shape of SF4​?	See-saw or Distorted Tetrahedral.

Part 3: Hybridization and Polarity

Q. No.	Question	Answer
40	Define Hybridization.	The process of intermixing of atomic orbitals of slightly different energies to form a new set of equivalent orbitals.
41	How many sp hybrid orbitals are formed from one s and one p orbital?	Two sp hybrid orbitals.
42	What is the geometry and bond angle of sp2 hybridization?	Trigonal Planar, 120∘.
43	What is the geometry and bond angle of sp3 hybridization?	Tetrahedral, 109.5∘.
44	What is the percentage of s-character in an sp hybrid orbital?	50%.
45	What is the hybridization of the central atom in BeCl2​?	sp (Linear, 180∘).
46	What is the hybridization of the C atom in C2​H4​ (Ethene)?	sp2 (Trigonal Planar).
47	What is the hybridization of the central N atom in NH3​?	sp3.
48	What is the hybridization of C in CO2​?	sp (Linear).
49	What is a Polar Covalent Bond?	A covalent bond where the shared electron pair is unequally attracted by the two atoms (due to EN difference).
50	Define Dipole Moment (μ).	The product of the magnitude of the charge (q) and the distance (d) between the centres of positive and negative charges (μ=q×d).
51	What is the SI unit of Dipole Moment?	Coulomb meter (C m), usually expressed in Debye (D).
52	Is CO2​ a polar or non-polar molecule?	Non-polar (due to linear shape, dipoles cancel out).
53	Is H2​O a polar or non-polar molecule?	Polar (due to bent shape, net dipole moment).
54	Arrange HCl,HF,HBr,HI in increasing order of bond polarity.	HI<HBr<HCl<HF (based on EN difference).
55	Which molecule among NH3​ and NF3​ has a higher dipole moment?	NH3​ (Lone pair and N-H bond dipoles are in the same direction, adding up).
56	If a molecule has a net dipole moment of zero, what does it usually imply about its structure?	It has a symmetrical structure.

Part 4: Molecular Orbital Theory (MOT) and Resonance

Q. No.	Question	Answer
57	What is the fundamental concept of Molecular Orbital Theory (MOT)?	Atomic orbitals combine to form an equal number of Molecular Orbitals (MOs).
58	What is an LCAO?	Linear Combination of Atomic Orbitals.
59	What are the two types of molecular orbitals formed by LCAO?	Bonding Molecular Orbitals (BMO) and Anti-Bonding Molecular Orbitals (ABMO).
60	Which MO is lower in energy, BMO or ABMO?	BMO (stabilizing, increases electron density between nuclei).
61	Write the formula for Bond Order according to MOT.	Bond Order=1/2(Nb​−Na​) (Nb​= e− in BMO, Na​= e− in ABMO).
62	What does a zero or negative bond order indicate?	The molecule is unstable and does not exist.
63	Is He2​ stable? Justify using bond order.	No, Bond Order = 0 (σ1s2​σ1s∗2​).
64	What is the bond order of O2​?	2 (Double bond).
65	What is the bond order of O2+​?	2.5.
66	What is the bond order of O2−​ (Superoxide ion)?	1.5.
67	What magnetic property does a molecule with unpaired electrons exhibit?	Paramagnetism.
68	What magnetic property does a molecule with all paired electrons exhibit?	Diamagnetism.
69	Is O2​ (Oxygen) paramagnetic or diamagnetic?	Paramagnetic (two unpaired e− in π∗2p orbitals).
70	Is N2​ (Nitrogen) paramagnetic or diamagnetic?	Diamagnetic (all electrons are paired).
71	What are Resonance Structures (or Canonical Forms)?	Two or more Lewis structures that collectively describe the electronic structure of a single molecule.
72	What is the Resonance Hybrid?	The actual structure of the molecule which is the intermediate of all resonance structures.
73	Give one example of a molecule that exhibits resonance.	O3​ (Ozone), CO32−​ (Carbonate ion), or Benzene (C6​H6​).
74	How does resonance affect the stability of a molecule?	Resonance increases the stability of the molecule.
75	What is the bond order of CO32−​?	4/3 or 1.33 (four bonds shared among three sites).

Part 5: Fajan's Rules and Intermolecular Forces

Q. No.	Question	Answer
76	What do Fajan's Rules predict?	The degree of covalent character in an ionic bond.
77	According to Fajan's Rules, which ion favors maximum covalent character?	Small Cation and Large Anion.
78	Why does a small cation favor covalent character?	Its high polarizing power (high charge density).
79	Define Polarizability of an ion.	The ability of an anion's electron cloud to be distorted by the cation.
80	Rank the following in increasing covalent character: LiCl,NaCl,KCl.	KCl<NaCl<LiCl (Cation size K+>Na+>Li+).
81	What type of attraction exists in a purely ionic solid?	Electrostatic (Coulombic) attraction.
82	What are Intermolecular Forces (IMFs)?	Attractive forces between molecules.
83	What are the five major types of Intermolecular Forces?	Dispersion (London) forces, Dipole-Dipole, Dipole-Induced Dipole, Ion-Dipole, Hydrogen Bonding.
84	Which type of IMF is present in all molecules?	London Dispersion Forces (or Van der Waals forces).
85	What is the strongest type of IMF?	Hydrogen Bonding.
86	What is Hydrogen Bonding?	A special case of dipole-dipole interaction between an H atom bonded to a highly electronegative atom (F,O,N) and another electronegative atom.
87	Why does water have an unusually high boiling point?	Extensive Hydrogen Bonding.
88	What is the difference between Intramolecular and Intermolecular H-bonding?	Intra is within the same molecule; Inter is between two different molecules.
89	Which type of H-bonding is responsible for the associated nature of alcohols?	Intermolecular H-bonding.

Part 6: Miscellaneous Concepts and Hybridization Details

Q. No.	Question	Answer
90	What are the main limitations of the Octet Rule?	Incomplete/Expanded octets, and it fails for odd-electron molecules.
91	What is the maximum number of lone pairs on the central atom in XeF2​?	Three (linear shape, sp3d hybridization).
92	What is the hybridization of the central atom in H2​O?	sp3 (two bond pairs, two lone pairs).
93	What is the hybridization of the central atom in ICl4−​?	sp3d2.
94	What is the type of overlap in a C-C single bond in C2​H6​?	sp3−sp3 σ overlap.
95	What is the type of overlap in a C-H bond in CH4​?	sp3−s σ overlap.
96	Define Bond Order (classical definition).	The number of bonds between two atoms in a molecule.
97	What is the general electronic configuration of the ABMO for a p orbital combination?	$\pi^ 2p$* and $\sigma^ 2p$*.
98	What is the covalent character of a compound where the electronegativity difference is >1.7?	Predominantly Ionic.
99	What is the covalent character of a compound where the electronegativity difference is ≈0?	Predominantly Covalent (pure covalent).
100	Why is the s-character of a hybrid orbital important?	Higher s-character leads to shorter bond length and greater bond strength.
101	What is the shape of a molecule with sp3d hybridization and one lone pair?	See-saw.
102	What is the shape of a molecule with sp3d hybridization and three lone pairs?	Linear.
103	What is the maximum possible bond order for a diatomic molecule?	3 (as in N2​ and CO).
104	What is the common oxidation state of a Group 1 element in an ionic compound?	+1.
105	Which carbon atom is sp2 hybridized in CH3​CHO (Acetaldehyde)?	The Carbonyl Carbon (>C=O).
106	Why are ionic compounds hard and brittle?	Strong electrostatic forces lead to a rigid structure, and displacement causes repulsion between same-charged ions.
107	Why are LiCl and MgCl2​ more covalent than KCl and CaCl2​?	Smaller Li+ and Mg2+ cations have higher polarizing power (Fajan's Rule).
108	Is ice denser than liquid water? Why?	No, due to the open cage-like structure formed by H-bonding in the solid state.
109	What is the geometry of the CO32−​ ion?	Trigonal Planar.
110	Name the only non-metal that typically forms an ionic bond with metals.	Fluorine (F) (due to its highest electronegativity).
111	Name the type of hybrid orbitals involved in sp3d2 hybridization.	one s, three p, and two d orbitals.