Concept: This question tests the understanding of Lewis dot structures, formal charges, and molecular geometry.

Why (C) is incorrect:

Lewis dot structures primarily show the connectivity of atoms and the distribution of valence electrons (bonding and non-bonding pairs) in a molecule or polyatomic ion. While they help in predicting the number of bonds and lone pairs around a central atom, they do not directly represent the three-dimensional arrangement of atoms or the actual shape of the molecule. Molecular geometry (actual shape) is determined by the VSEPR (Valence Shell Electron Pair Repulsion) theory, which considers the repulsion between electron pairs around the central atom.

Option Analysis:

• A) The lowest energy structure is the one which has the smallest formal charges on the atoms. This statement is correct. One of the rules for determining the most stable (lowest energy) Lewis structure among several resonance structures is to choose the one where formal charges are minimized, and if formal charges are unavoidable, negative formal charges should reside on the more electronegative atoms.
• B) Formal charges do not indicate the real charge separation within the molecule. This statement is correct. Formal charges are a theoretical tool used to help determine the most plausible Lewis structure. They are based on the assumption that electrons in a bond are shared equally, which is often not the case in reality due to differences in electronegativity. Real charge separation is better described by concepts like bond polarity and dipole moments.
• C) Lewis dot structures represent the actual shapes of the molecules. This statement is incorrect. Lewis structures show 2D connectivity and electron distribution, not 3D shape. Molecular geometry is determined by VSEPR theory.
• D) In case of polyatomic ions, the net charge is possessed by the ion as a whole and not by a particular atom. This statement is correct. The net charge of a polyatomic ion is distributed over the entire ion, although formal charges can be assigned to individual atoms to help understand electron distribution. The charge is delocalized across the structure, especially in cases of resonance.

Correct Answer: (C)