Some chemists believe that satisfaction of the octet rule should be the top criterion for choosing the dominant Lewis structure of a molecule or ion. Other chemists believe that achieving the best formal charges should be the top criterion. Consider the dihydrogen phosphate ion, H₂PO₄^-, in which the H atoms are bonded to O atoms. (a) What is the predicted dominant Lewis structure if satisfying the octet rule is the top criterion?

Key Concepts

Octet Rule

The octet rule is a chemical guideline that states atoms tend to bond in such a way that they each have eight electrons in their valence shell, achieving a stable electron configuration similar to that of noble gases. This rule is particularly relevant for main group elements and helps predict the bonding behavior and structure of molecules, including the arrangement of electrons in Lewis structures.

Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms in a molecule and the lone pairs of electrons that may exist. They are used to visualize the arrangement of electrons and to predict the geometry and reactivity of molecules. In constructing Lewis structures, one must consider the octet rule, formal charges, and the overall charge of the molecule or ion.

Formal Charge

Formal charge is a theoretical charge assigned to an atom in a molecule, calculated based on the number of valence electrons, the number of non-bonding electrons, and the number of bonds. It helps in determining the most stable Lewis structure by minimizing the formal charges across the molecule. A structure with the lowest formal charges is often preferred, but it must also satisfy the octet rule for the atoms involved.