Understanding Lewis Structures and the Octet Rule

The video tutorial covers exceptions to the octet rule in Lewis structures. It explains how some molecules, like BH3, have incomplete octets, while others, such as PCl5 and ICl5, have expanded octets. The tutorial also discusses molecules with odd numbers of electrons, like NO and NO2, and how these violate the octet rule. Key concepts include the limitations of second-row elements and the ability of third-row elements to have expanded octets.

What is the main reason BH3 does not follow the octet rule?

• Boron has only six valence electrons available.

• Boron prefers to have a full d-orbital.

• Boron can only form two bonds.

• Hydrogen can only form one bond.

Which of the following elements can have an expanded octet?

• Nitrogen

• Phosphorus

• Carbon

• Fluorine

Why can't second-row elements have expanded octets?

• They have a full s-orbital.

• They have too many electrons.

• They lack d-orbitals.

• They are too electronegative.

In the Lewis structure of PCl5, how many electrons surround the phosphorus atom?

• 10

• 12

• 8

• 14

What is the molecular geometry of iodine pentachloride (ICl5)?

• Tetrahedral

• Square pyramidal

• Linear

• Trigonal planar

Why do molecules with an odd number of electrons violate the octet rule?

• They have too many bonds.

• They cannot distribute electrons evenly.

• They have an excess of lone pairs.

• They are too reactive.

In the most stable Lewis structure of NO, which atom has a complete octet?

• Nitrogen

• Oxygen

• Both

• Neither

For NO2, why can't nitrogen have a complete octet?

• It forms too many bonds.

• It has an odd number of electrons.

• It is too electronegative.

• It lacks d-orbitals.

How many lone pairs are present on the nitrogen atom in the Lewis structure of NO2?

• 0

• 1

• 3

• 2

What is the total number of valence electrons in the NO2 molecule?

• 15

• 18

• 16

• 17