Ch 04 - Chemical Bonding and Molecular Structure11th Chemistry
The Octet Rule and its Foundation
What is the core principle of the Octet Rule formulated by Kössel and Lewis, and which group of elements inspired it?
What is the core principle of the Octet Rule formulated by Kössel and Lewis, and which group of elements inspired it?
Principle: Atoms combine by transferring (losing/gaining) or sharing valence electrons to attain a stable outer shell of exactly eight electrons.
Inspiration: The chemical inertness and high stability of Noble Gases, which naturally possess a complete octet ( configuration, except Helium, which has a duplet).
Prism Memory Hook
Octet = Eight is Great (Noble Gas State).
Formal Charge Formula
Formal Charge Formula
State the formula used to calculate the formal charge of an individual atom within a polyatomic molecule or ion.
Variables & Units:
- V = Total number of valence electrons in the free atom
- N = Total number of non-bonding (lone pair) electrons
- B = Total number of bonding (shared) electrons
Conditions/Notes:
- The Lewis structure with the smallest formal charges on atoms is generally the lowest energy (most stable) structure.
- It is a theoretical bookkeeping tool assuming pure covalent bonding with equal sharing of electron pairs, not actual charge separation.
Prism Memory Hook
Valence minus Non-bonding minus Half the Bonding.
Exceptions to Octet Rule: Incomplete & Odd-Electron
What are 'incomplete octet' and 'odd-electron' molecules? Provide common examples of each.
What are 'incomplete octet' and 'odd-electron' molecules? Provide common examples of each.
Incomplete Octet: Central atoms with fewer than 4 valence electrons can form stable covalent compounds without completing an octet.
Examples: , , .
Odd-Electron Molecules: Molecules with an odd total number of electrons physically cannot satisfy the octet rule for all atoms simultaneously.
Examples: Nitric Oxide () and Nitrogen Dioxide ().
Prism Memory Hook
LiBeB (Little Bears Bite) for incomplete; NO and NO2 for odd.
Also in this chapter
40 more cards to study in Prism
- 4Exceptions to Octet Rule: Expanded Octet
- 5Favourable Conditions for Ionic Bonds
- 6Lattice Enthalpy Definition
- 7Coordination Numbers: NaCl vs. CsCl
- 8Dipole Moment ($\mu$)
- 9Pseudo Inert Gas Configuration
- 10Fajans' Rules (Covalent Character)
- 11The Metallic Bond (Electron-Sea Model)
- 12Covalent vs. Van der Waals Radius
- 13Average Bond Enthalpy
- 14Coordinate Covalent (Dative) Bond
- 15Resonance and Resonance Energy
- 16Dipole Moment Anomaly: NH3 vs NF3
- 17VSEPR Theory: Order of Repulsion
- 18VSEPR Geometries (Zero Lone Pairs)
- 19Predicting Hybrid State (Steric Number)
- 20Bond Angle Deviations: CH4, NH3, H2O
- 21PCl5: Axial vs. Equatorial Bonds
- 22Valence Bond Theory (VBT): Orbital Overlap
- 23Positive, Negative, and Zero Orbital Overlap
- 24Sigma (\sigma) vs. Pi ($\pi$) Bonds
- 25Bond Order (MOT)
- 26Hybridisation Concept
- 27sp, $sp^2$, and $sp^3$ Geometries
- 28Multiple Bonds in Ethene and Ethyne
- 29Hybridisation Involving d-Orbitals
- 30Molecular Orbital Theory (MOT) Basics
- 31Bonding vs. Antibonding Molecular Orbitals
- 32Percentage Ionic Character
- 33MO Energy Sequence: Oxygen & Fluorine
- 34Bond Order, Length, and Enthalpy
- 35Bond Order of Isoelectronic Species
- 36Magnetic Nature in MOT
- 37The Paramagnetism of Oxygen ($O_2$)
- 38Born-Lande Equation (Lattice Energy)
- 39Non-existence of $He_2$
- 40The Unique Bonding in $C_2$
- 41Delocalised Pi Bonds in 1,3-Butadiene
- 42Hydrogen Bonding
- 43Intermolecular vs. Intramolecular H-Bonding
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