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S1.1 - Introduction to the particulate nature of matter S1.2 - The nuclear atom S1.3 - Electron configurations S1.4 - Counting particles by mass - The mole S1.5 - Ideal gases S2.1 - The ionic model S2.2 - The covalent model S2.3 - The metallic model S2.4 - From models to materials S3.1 - The periodic table - Classification of elements S3.2 - Functional groups - Classification of organic compounds R1.1 - Measuring enthalpy changes R1.2 - Energy cycles in reactions R1.3 - Energy from fuels R1.4 - Entropy and spontaneity AHL R2.1 - How much? The amount of chemical change R2.2 - How fast? The rate of chemical change R2.3 - How far? The extent of chemical change R3.1 - Proton transfer reactions R3.2 - Electron transfer reactions R3.3 - Electron sharing reactions R3.4 - Electron-pair sharing reactions

S2.2 - The covalent model

2.2.1 Covalent Bonds and Lewis Formulas 2.2.2 Bond Types 2.2.3 Co-coordination (Dative) Bonds 2.2.4 VSEPR Shapes of Molecules 2.2.5 Electronegativity and Bond Polarity 2.2.6 Polarity and Dipole Moments 2.2.7 Covalent Network Structures and Allotropes 2.2.8 Intermolecular Forces 2.2.9 Physical Properties of Covalent Substances 2.2.10 Chromatography and Intermolecular Forces 2.2.11 Resonance Structures (AHL) 2.2.12 Benzene and Resonance (AHL) 2.2.13 Expanded Octet and VSEPR (AHL) 2.2.14 Formal Charge (AHL) 2.2.15 Sigma and Pi Bonds (AHL) 2.2.16 Hybridization (AHL)

Formal Charge and Lewis Structures HL Only

Specification Reference S2.2.14

Quick Notes:

  • Formal charge is a tool for evaluating the most likely Lewis structure of a species.
  • It assumes electrons in bonds are shared equally.
  • Formula: Formal charge
    = (valence electrons) − (non-bonding electrons) − ½(bonding electrons)
  • The most stable Lewis structure:
    • Has the lowest total formal charge
    • Has formal charges closest to zero
    • Places negative charges on the more electronegative atoms

Full Notes:

What Is Formal Charge?

Formal charge (FC) is a theoretical charge on an atom, assuming electrons are shared equally in bonds in a compound.

It helps identify the most accurate Lewis structure and understand electron distribution in a molecule or ion.

Formal Charge Formula

To calculate formal charge for any atom:

IB Chemistry formal charge equation showing valence electrons minus non-bonding electrons minus half bonding electrons.

Example:The Nitrate Ion (NO3−)

IB Chemistry nitrate ion resonance structure showing nitrogen double bonded to one oxygen and single bonded to two other oxygens with charges.

In the nitrate ion:

This means overall the charge of the nitrate ion is −1 (+1 + (−1) + (−1) = −1).

Guidelines for Using Formal Charge

A preferred Lewis structure will:

Summary