Depicting Molecules and Ions with Lewis Structures

1 DEPICTING MOLECULES AND IONS WITH LEWIS STRUCTURES 

The first step toward visualizing what a molecule looks like is to convert its molecular formula to its Lewis structure (or Lewis formula). This two-dimensional structural formula consists of electron-dot symbols that depict each atom and its neighbors, the bonding pairs that hold them together, and the lone pairs that fill each atom s outer level (valence shell). In many cases, the octet rule (Section 9.1) guides us in allotting electrons to the atoms in a Lewis structure in many other cases, however, we set the rule aside. 

Concepts Skills to Review Before You Study This Chapter 

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Depicting Molecules and Ions with Lewis Structures... 

Depicting Molecules and Ions with Lewis Structures Using the Octet Rule Resonance Formal Charge Exceptions to the Octet Rule... 

Because all three bonds are identical, a better model of the nitrate ion is a blend of all three Lewis structures with each bond intermediate in properties between a single and a double bond. This blending of structures, which is called resonance, is depicted in (9) by double-headed arrows. The blended structure is a resonance hybrid of the contributing Lewis structures. A molecule does not flicker between different structures a resonance hybrid is a blend of structures, just as a mule is a blend of a horse and a donkey, not a creature that flickers between the two. 

From these experiments, Lorand and Edwards concluded that the conjugate base of phenylboronic acid has a tetrahedral, rather than trigonal structure. The dissociation of a hydrogen ion from phenylboronic acid occurs from the interaction of the boron atom with a molecule of water. As the phenylboronic acid and water react, a hydrated proton is liberated, thereby defining the acidity constant K, see Hartley, Phillips and James. This is depicted in heme 5 by considering an explicit water molecule associated with the Lewis acidic boron. The reported pK s of phenylboronic acid fluctuate between 8.7 and 8.9, with a recent in-depth potentiometric titration study refining this value to 8.70 in water at 25°C. ... 

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