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Syllabus
🩺 NEET UG
Subject:Chemistry Syllabus

Chemical Bonding

Syllabus Unit: Physical Chemistry

Why it matters

Chapter overview

This topic covers how atoms combine into compounds — electron transfer or sharing that forms ionic and covalent bonds, VSEPR theory's prediction of 3D molecular geometry from electron-pair repulsion, the hybrid-orbital model that explains observed shapes and bond parameters, and the dipole moment and resonance concepts that refine the simple Lewis-structure picture.

Chemistry Syllabus Physical Chemistry ~25% weightage
Live Animation1 / 4
90
NaCl (Ionic, mp 801°C)
20
H2O (Polar Covalent, mp 0°C)
5
CH4 (Nonpolar Covalent, mp -182°C)

1Ionic & Covalent Bonding

Ionic bonds form by complete electron transfer between atoms of very different electronegativity; covalent bonds form by sharing electron pairs between similar atoms.

Learning Objectives

  • Explain ionic bond formation via electron transfer and lattice energy stabilisation.
  • Explain covalent bond formation via electron-pair sharing and draw simple Lewis structures.
  • State the octet rule and identify common exceptions (BF3, PCl5, NO).
  • Distinguish the physical properties (melting point, conductivity, solubility) of ionic vs covalent compounds.

Key Terms

Ionic BondElectrostatic attraction between oppositely charged ions formed by complete electron transfer, typically metal + non-metal.
Covalent BondBond formed by mutual sharing of one or more electron pairs between two atoms, typically non-metal + non-metal.
Lattice EnergyEnergy released when gaseous ions combine to form one mole of an ionic solid crystal; higher lattice energy means greater ionic stability.
Octet RuleAtoms tend to gain, lose or share electrons to attain 8 electrons in their valence shell, resembling the nearest noble gas.

Electronegativity difference is the deciding factor between the two bonding extremes: a large gap favours complete electron transfer (ionic); a small gap favours electron sharing (covalent).

Ionic bonding

  • Forms between an atom of low ionisation enthalpy (a metal, e.g. Na) and one of high electron affinity (a non-metal, e.g. Cl).
  • The resulting electrostatic attraction is non-directional, so ions pack into a crystal lattice rather than forming discrete molecules.
  • Favoured by high lattice energy — the energy released on assembling the ionic crystal from gaseous ions.
Na (…3s¹) → Na⁺ + e⁻ Cl (…3p⁵) + e⁻ → Cl⁻ Na⁺ + Cl⁻ → NaCl (lattice)

Covalent bonding

  • Formed by one or more shared electron pairs between atoms of similar electronegativity, producing directional bonds and discrete molecules.
  • Single, double and triple bonds correspond to 1, 2 or 3 shared electron pairs.
  • A coordinate (dative) bond is a special covalent bond where both shared electrons come from just one atom, e.g. the fourth N–H bond in NH4⁺.
Common MistakeOctet rule exceptions are common NEET traps: BF3 (only 6 electrons around B, incomplete octet), PCl5 and SF6 (expanded octet using d-orbitals), and NO (an odd-electron molecule that can never satisfy the octet rule).

Comparing properties

Ionic compounds have high melting/boiling points and conduct electricity when molten or dissolved (free-moving ions), while covalent (molecular) compounds have lower melting points and are poor conductors since they carry no free ions.