Resonance Structures and Formal Charges

The video tutorial explains how to handle situations where multiple correct Lewis structures can be drawn for a molecule, focusing on resonance structures and formal charge. It uses the thiocyanate ion (SCN-) as an example, detailing the process of counting valence electrons, drawing possible resonance structures, and calculating formal charges. The tutorial concludes by determining the best resonance structure based on formal charges and electronegativity.

What is the term used when more than one valid Lewis structure can be drawn for a molecule?

• Molecular configurations

• Resonance structures

• Hybrid structures

• Isomers

How many total valence electrons are present in the thiocyanate ion (SCN-)?

• 14

• 15

• 16

• 17

Which of the following is NOT a possible resonance structure for the thiocyanate ion?

• Sulfur single bonded to carbon, nitrogen triple bonded to carbon

• Sulfur double bonded to carbon, nitrogen double bonded to carbon

• Sulfur single bonded to nitrogen, carbon triple bonded to nitrogen

• Sulfur triple bonded to carbon, single bonded to nitrogen

What is the definition of resonance in chemistry?

• The sharing of electrons between two atoms

• The presence of multiple valid Lewis structures for a molecule

• The formation of a double bond in a molecule

• The ability of a molecule to rotate around a single bond

How is the formal charge of an atom in a molecule calculated?

• By subtracting the number of unshared electrons and bonds from the number of valence electrons

• By subtracting the number of bonds from the number of valence electrons

• By adding the number of unshared electrons and bonds

• By adding the number of valence electrons and bonds

What is the formal charge of sulfur in the thiocyanate ion when it has 6 valence electrons, 4 unshared electrons, and 2 bonds?

• -1

• -2

• 0

• +1

In the thiocyanate ion, which atom carries the negative charge in the structure with the lowest formal charges?

• Oxygen

• Nitrogen

• Carbon

• Sulfur

Which rule helps determine the best resonance structure when formal charges are equal?

• The structure with the least number of atoms

• The structure with the most bonds

• The structure with negative charges on the more electronegative atoms

• The structure with the most lone pairs

What is the formal charge of nitrogen in the thiocyanate ion when it has 5 valence electrons, 2 unshared electrons, and 3 bonds?

• -1

• 0

• -2

• +1

Why is the resonance structure with the negative charge on nitrogen considered the best for the thiocyanate ion?

• Because it has the least number of lone pairs

• Because it has the most bonds

• Because nitrogen is less electronegative than sulfur

• Because nitrogen is more electronegative than sulfur