Which of the following is a reason why a Lewis dot structure might be considered invalid, especially in the context of exceptions to the octet rule?

• A. The structure includes lone pairs on all atoms, even those that typically do not have them.
• B. The central atom has more than eight electrons, violating the octet rule.
• C. All atoms have exactly eight electrons, including hydrogen.
• D. The structure shows only single bonds for all atoms, regardless of their usual bonding patterns.

Answer: (B)

Verified step by step guidance

1. Understand that Lewis dot structures are a way to represent the valence electrons of atoms in a molecule, showing how atoms share or transfer electrons to achieve stable electron configurations.
2. Recall the octet rule, which states that atoms tend to form bonds until they are surrounded by eight valence electrons, but note that there are exceptions to this rule, especially for elements in period 3 or beyond that can have expanded octets.
3. Identify that a Lewis structure might be considered invalid if it violates fundamental bonding principles, such as having a central atom with more than eight electrons when the atom is not capable of expanding its octet (common for second-period elements like carbon, nitrogen, and oxygen).
4. Evaluate the options given: having lone pairs on all atoms is not necessarily invalid, as some atoms do have lone pairs; all atoms having exactly eight electrons including hydrogen is incorrect because hydrogen follows the duet rule (2 electrons); only single bonds regardless of bonding patterns can be incorrect but is not the main reason for invalidity related to the octet rule.
5. Conclude that the key reason a Lewis structure might be invalid in this context is when the central atom has more than eight electrons, violating the octet rule for atoms that cannot expand their octet.