Chemical Bonding and Molecular Structure — Syllabus
Punjab Board · Class 11 · Chemistry
What Chemical Bonding and Molecular Structure covers in Punjab Board Class 11 Chemistry: 4 topics, for the 2026-27 session.
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Topics in Chemical Bonding and Molecular Structure
1. Kössel-Lewis Approach to Chemical Bonding
- Atoms combine to achieve the electronic configuration of the nearest noble gas (octet rule).
- Lewis pictured atoms as a positively charged 'Kernel' (nucleus + inner electrons) surrounded by an outer shell of up to 8 electrons.
- Lewis symbols represent valence electrons as dots around the chemical symbol of an element.
2. Ionic (Electrovalent) Bond and Lattice Enthalpy
- Ionic bond forms by transfer of electrons from a metal (low ionization enthalpy) to a non-metal (high electron gain enthalpy).
- Example: Na loses one electron to form Na⁺; Cl gains one electron to form Cl⁻. They attract each other electrostatically.
- Ionic compounds form a 3D crystal lattice structure (e.g., NaCl rock salt structure).
3. Bond Parameters: Length, Angle, Enthalpy, Order, and Polarity
- Bond Length: Equilibrium distance between nuclei of two bonded atoms. Measured in picometres (pm). Single bond > Double bond > Triple bond in length.
- Bond Angle: Angle between two adjacent bonds at the central atom. Determines molecular geometry.
- Bond Enthalpy: Energy required to break 1 mole of a bond in the gaseous state. Higher bond order = higher bond enthalpy.
4. Limitations of the Octet Rule
- The octet rule is useful but NOT universal. It mainly works for second-period elements.
- Exception 1 – Incomplete Octet: Central atom has fewer than 8 electrons. Examples: LiCl (2e on Li), BeH2 (4e on Be), BCl3 and BF3 (6e on B), AlCl3.
- Exception 2 – Odd-electron Molecules: Molecules with an odd number of electrons cannot satisfy the octet rule for all atoms. Examples: NO (11 electrons), NO2 (17 electrons).
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