The concept of ionic and covalent bonds is where NEET tests whether you actually understand why atoms bond, not just that they bond. A common confusion: treating ionic and covalent as a binary switch. They are endpoints on a continuum — most real bonds have partial ionic and partial covalent character.
Ionic bond forms when one atom transfers one or more electrons to another, producing oppositely charged ions held by electrostatic attraction. This typically occurs between elements with a large electronegativity difference (generally > 1.7, though this threshold is approximate). Metals from Groups 1 and 2 with nonmetals from Groups 16 and 17 are classic examples: NaCl, MgO, CaF₂.
Covalent bond forms when two atoms share one or more electron pairs. When the sharing is equal (same atoms or negligible electronegativity difference), the bond is nonpolar covalent: H₂, Cl₂, N₂. When sharing is unequal, the bond is polar covalent: HCl, H₂O.
Key NCERT distinction (Class 11 Chemistry Chapter 4, page 2): a chemical bond is the attractive force that holds two atoms together. The octet rule — atoms tend to achieve eight electrons in their valence shell — drives both bond types, but through different mechanisms: electron transfer (ionic) versus electron sharing (covalent).
Watch-out for NEET: Questions test whether you can identify bond type from electronegativity difference, distinguish lattice structures from molecular structures, and recognise that "ionic" does not automatically mean "solid at room temperature" — it means a lattice of ions with high melting point, electrical conductivity when molten or dissolved, but not when solid.
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
Which of the following best describes an ionic bond?
In which of the following compounds is the bond predominantly covalent?
Which property is characteristic of ionic compounds?
The electronegativity values of atoms X and Y are 0.9 and 3.5 respectively. The bond formed between X and Y is most likely:
Which of the following molecules contains a nonpolar covalent bond?
An ionic compound is dissolved in water and the solution conducts electricity. The same compound in the solid state does not conduct. This is because:
A student claims that since MgO and NaCl are both ionic, they should have nearly identical melting points. What is wrong with this reasoning?
Consider the series: NaF, NaCl, NaBr, NaI. As we go from NaF to NaI, the ionic character of the bond:
Given
A compound is formed between element A (electronegativity = 1.0) and element B (electronegativity = 3.0). The compound has a melting point of 801 °C, does not conduct electricity as a solid, but conducts when dissolved in water.
Required
Identify the bond type and justify using both electronegativity data and observed properties.
Concept
Bond type can be predicted from the electronegativity difference between bonded atoms. A large difference (generally > 1.7) indicates ionic bonding. Ionic compounds exhibit: high melting points (strong lattice), no solid-state conductivity (fixed ions), and conductivity in solution (free ions).
Formula
Electronegativity difference = |EN_B − EN_A|
Substitution
ΔEN = |3.0 − 1.0| = 2.0
Calculation
ΔEN = 2.0, which exceeds the ~1.7 threshold, indicating predominantly ionic bonding. Cross-check with properties: - High melting point (801 °C) ✓ — consistent with ionic lattice - No solid-state conductivity ✓ — ions fixed in lattice - Conductivity in aqueous solution ✓ — free ions in water All three observations confirm ionic bonding.
Final answer
The bond between A and B is **ionic**. The electronegativity difference of 2.0 and all three observed properties (high MP, no solid conductivity, solution conductivity) are consistent with ionic bonding.
Common trap
Concluding "ionic" from electronegativity difference alone without verifying against properties, or vice versa. NEET questions sometimes give a compound with a borderline ΔEN (~1.7) where properties become the deciding factor. Always use both criteria when available.
Similar NEET-style question
A compound AB₂ has ΔEN = 1.8, melts at 714 °C, and conducts electricity when molten but not when solid. A student argues the bond is "polar covalent because ΔEN is close to 1.7." Is the student correct? Justify. (Answer: No — the properties (high MP, conduction only when molten) are definitive markers of ionic bonding. The ΔEN of 1.8 supports ionic character. Borderline ΔEN values require property-based confirmation, which here clearly points to ionic.) ---
Ionic bond: electrostatic attraction between cation and anion (electron transfer). Covalent bond: sharing of electron pair between two atoms. Polar covalent: unequal sharing due to electronegativity difference.
-- NCERT Class 11 Chemistry, Ch. 4, p. 2Higher bond order: shorter, stronger bond. N₂: BO=3, O₂: BO=2, F₂: BO=1.
| Symbol | Quantity | SI Unit |
|---|---|---|
| N_b | bonding electrons | - |
| N_a | antibonding electrons | - |
| BO | bond order | - |
Product of charge magnitude and bond length. SI: C·m. Common: Debye (1 D = 3.336e-30 C·m).
| Symbol | Quantity | SI Unit |
|---|---|---|
| q | charge | C |
| d | bond length | m |
| mu | dipole moment | C*m or D |
These are the exact patterns that cause wrong answers in NEET. Each trap includes when it triggers and how to avoid it.
Category: Inorganic Exception
Student counts only bonded atoms when assigning hybridization. Lone pairs count toward steric number too. Steric number = bond pairs + lone pairs → hybridization.
Molecule with central atom having lone pairs (e.g., NH₃: 3 bonds + 1 lp = 4 = sp³; H₂O: 2+2 = 4 = sp³).
Steric number formula: SN = (bond pairs) + (lone pairs). SN=2: sp; SN=3: sp²; SN=4: sp³; SN=5: sp³d; SN=6: sp³d². Lone pairs distort but still count.
Root cause: concept gap
Steric number = bond pairs + lone pairs. NH3: SN=4 → sp³ (despite trigonal pyramidal shape).
Root cause: concept gap
Memorise the ordering switch at N2/O2 boundary. Affects bond order and magnetic property predictions.
Root cause: formula misuse
BO = (Nb - Na)/2. Antibonding electrons subtract. F2: 8 bonding, 6 antibonding → BO = 1.
14 questions from NEET 2021, 2022, 2023, 2024, 2025. Answers verified against NTA official keys.
The element expected to form largest ion to achieve the nearest noble gas configuration is
Which statement regarding polymers is not correct?
Amongst the following which one will have maximum ‘lone pair - lone pair’ electron repulsions?
In one molal solution that contains 0.5 mole of a solute, there is
Which of the following molecules is non-polar in nature?
Recurring question shapes from past papers. Each pattern shows why wrong options look tempting.
ignores lone pairs
Counts only bonding pairs
forgets anti bonding
Counts only bonding electrons
ignores lp bp distortion
Doesn't adjust for lone-pair repulsion
Test yourself on this topic with real past-paper questions:
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