Question

Revise (as necessary) your checklist that can be used to determine if a Lewis structure for a molecule is correct.

Short answer

A correct Lewis structure should correctly represent a molecule's total valence electrons, adapt to the Octet rule, have zero or close to zero formal charges and have correctly placed double/triple bonds.

Step-by-step solution

Understand the concept of Lewis structures

Lewis structures, also known as electron dot diagrams, visually represent the arrangement of atoms within a molecule, along with any unbonded electrons and bonding pairs of electrons. Creating a valid Lewis structure is crucial for understanding the molecule's shape, polarity, and other properties. The structure must correctly illustrate the total number of valence electrons present in the molecule.

Ensure that atoms follow the Octet rule

The Octet rule states that atoms seek to have eight electrons in their valence shell to achieve a stable configuration. The only exception to this rule is Hydrogen, which requires only two electrons for stability. When evaluating Lewis structures, make sure that all atoms (except Hydrogen) are surrounded by eight electrons. These can be through both shared (bonds) and unshared (lone pairs) electrons.

Check for the correct total number of valence electrons

The total number of electrons in the Lewis structure must be equal to the sum of the valence electrons of each atom in the molecule. To achieve this, remember that each bond represents two shared valence electrons. Unshared electrons, also called lone pairs, reside solely on one atom and are also part of the total.

Assess formal charges

A valid Lewis structure should have formal charges close to zero and any negative formal charges should be around more electronegative atoms. Formal charges are calculated by assuming that electrons in all chemical bonds are shared equally between atoms, regardless of the atoms' relative electronegativity.

Double and Triple Bonds

Make sure that there is proper placement of double and triple bonds. Not all atoms involved in the structure will always form single bonds. In some cases, double or triple bonds are required, especially when single bonds do not fulfill the Octet rule. Double and triple bonds also significantly contribute to the molecule's total electron count.