Ionic and Covalent Bonds — Revision Notes

⚡ 30-Second Revision

Key facts, numbers, article numbers in bullet format.

Ionic Bonds: — Electron transfer, metal + non-metal, ΔEN > 1.7. High MP/BP, conducts molten/aqueous. Examples: NaCl, MgO.
Covalent Bonds: — Electron sharing, non-metal + non-metal, ΔEN < 1.7. Low MP/BP (except network), non-conductive. Examples: H2O, CO2.
Electronegativity: — Atom's electron-attracting power. Determines bond type.
Polar Covalent: — Unequal sharing, ΔEN 0.4-1.7, partial charges, dipole moment (e.g., H2O).
Nonpolar Covalent: — Equal sharing, ΔEN < 0.4, no partial charges (e.g., Cl2, CH4).
Coordinate Bond: — Both electrons from one atom (e.g., NH4+).
Lattice Energy: — Strength of ionic bond, higher for smaller, higher-charged ions.

2-Minute Revision

For a quick two-minute revision, focus on the core distinctions and their immediate consequences. Ionic bonds form via electron transfer between metals and non-metals, driven by a large electronegativity difference (>1.

7). This leads to the formation of a crystal lattice of oppositely charged ions, resulting in high melting/boiling points, hardness, brittleness, and electrical conductivity only in molten or aqueous states.

Think NaCl. Covalent bonds, conversely, involve electron sharing between non-metals, with a smaller electronegativity difference. These form discrete molecules (or network solids like diamond). They generally have lower melting/boiling points, are poor conductors, and their solubility depends on polarity.

Polar covalent bonds (ΔEN 0.4-1.7, e.g., H2O) have unequal sharing and a dipole, while nonpolar covalent bonds (ΔEN < 0.4, e.g., Cl2) have equal sharing. Remember coordinate bonds as a special sharing case where one atom donates both electrons.

The Vyyuha approach emphasizes that these fundamental differences in electron behavior are the root cause of all observed property variations, a key insight for UPSC.

5-Minute Revision

A five-minute revision should consolidate the formation mechanisms, properties, and key examples, integrating the role of electronegativity. Start with Ionic Bonds: Formed by complete electron transfer from a metal to a non-metal, driven by a large electronegativity difference (ΔEN > 1.

7). This creates cations and anions, which are held together by strong electrostatic forces in a crystal lattice. The strength of this lattice is quantified by lattice energy, influenced by ion charge and size.

Properties include very high melting/boiling points, hardness, brittleness, and electrical conductivity only when molten or dissolved (due to mobile ions). Examples: NaCl, MgO, CaF2.

Next, Covalent Bonds: Formed by the mutual sharing of electrons between non-metals, with a smaller electronegativity difference (ΔEN < 1.7). This sharing can be equal (nonpolar covalent, ΔEN < 0.4, e.

g., Cl2, CH4) or unequal (polar covalent, ΔEN 0.4-1.7, e.g., H2O, NH3). Unequal sharing creates partial charges and a bond dipole. The overall molecular polarity depends on bond polarity and molecular geometry (e.

g., CO2 is nonpolar despite polar bonds due to linearity). Coordinate (dative) bonds are a special type where one atom donates both shared electrons (e.g., NH4+). Covalent compounds generally have lower melting/boiling points (due to weaker intermolecular forces), are poor conductors, and can be gases, liquids, or soft solids.

Exceptions are covalent network solids (diamond, SiO2) which have exceptionally high melting points and hardness due to continuous covalent bonding throughout. Application examples include ionic liquids in green chemistry and covalent drug-target interactions in pharmaceuticals.

Prelims Revision Notes

For Prelims, focus on high-recall facts and distinctions. Ionic Bonds: Formed by electron *transfer* (metal + non-metal). Large electronegativity difference (ΔEN > 1.7). Forms ions (cations, anions) and crystal lattice.

Properties: High melting/boiling points, hard, brittle. Conducts electricity *only* in molten or aqueous state (mobile ions). Insoluble in nonpolar solvents. Examples: NaCl, KBr, MgO, Al2O3. Covalent Bonds: Formed by electron *sharing* (non-metal + non-metal).

Small to moderate electronegativity difference (ΔEN < 1.7). Forms molecules. Properties: Generally low melting/boiling points, softer. *Does not* conduct electricity (localized electrons). Solubility varies ('like dissolves like').

Examples: H2O, CO2, CH4, O2, N2. Polar Covalent: Unequal sharing (ΔEN 0.4-1.7), partial charges (δ+/δ-), bond dipole. Molecular polarity depends on geometry (e.g., H2O is polar, CO2 is nonpolar). Nonpolar Covalent: Equal sharing (ΔEN < 0.

4), no partial charges. Coordinate Covalent: Both shared electrons from one atom (e.g., NH4+, H3O+). Covalent Network Solids: Giant molecules with continuous covalent bonds (e.g., Diamond, Graphite, SiO2) – exceptionally high MP/BP, hardness (except graphite).

Remember the VYYUHA BOND-MASTER mnemonic for quick recall.

Mains Revision Notes

For Mains, structure your revision around analytical frameworks. Core Concept: Chemical bonds arise from electron interactions to achieve stability. Ionic Bonds: Mechanism: Electron transfer (metal to non-metal) driven by large ΔEN, low IE of metal, high EA of non-metal.

Result: Electrostatic attraction between ions forming a crystal lattice. Properties & Reasons: High MP/BP (strong lattice energy, overcome by heat); Hard & Brittle (strong forces, but repulsion on displacement); Conductivity (mobile ions in molten/aqueous state, fixed in solid); Solubility (polar solvents, ion-dipole interactions).

Covalent Bonds: Mechanism: Electron sharing (non-metal to non-metal) due to smaller ΔEN. Result: Discrete molecules or network solids. Properties & Reasons: Low MP/BP (weak intermolecular forces, easily overcome); Non-conductive (localized electrons); Variable solubility (polarity matching).

Polarity: Bond polarity (ΔEN) vs. Molecular polarity (bond dipoles + geometry). Coordinate bonds are special covalent bonds. Applications: Connect bonding to real-world scenarios: Li-ion batteries (ionic mobility), pharmaceuticals (drug-target interactions, covalent inhibitors), environmental (ionic liquids, pollutant binding).

Use the 'Vyyuha Bond Prediction Matrix' to integrate ΔEN, atomic size, IE, and EA for comprehensive analysis. Emphasize mechanistic explanations for all property differences.

Vyyuha Quick Recall

VYYUHA BOND-MASTER

Valence Electrons: Key to all bonding interactions.
Yielding Electrons: Ionic bonds involve one atom yielding electrons.
Yoking Electrons: Covalent bonds involve atoms yoking (sharing) electrons.
Unequal Sharing: Leads to polar covalent bonds and dipoles.
High Electronegativity Difference: Predicts ionic bonds.
Applications: Remember real-world uses in batteries, drugs, environment.
Born-Haber: Conceptual cycle for lattice energy.
Octet Rule: Driving force for bond formation.
Network Solids: Covalent bonds forming giant structures (e.g., Diamond).
Dipole Moment: Molecular polarity depends on bond polarity and geometry.
Melting Points: High for ionic, low for molecular covalent.
Aqueous Conductivity: Ionic compounds conduct when dissolved.
Solubility: 'Like dissolves like' principle.
Transfer vs. Sharing: The core distinction.
Electrostatic Forces: Hold ionic compounds together.
Reactants: Metals + Non-metals for ionic; Non-metals + Non-metals for covalent.