Calculating Lone Pairs and Valence Electrons in Molecular Structures

The video tutorial explains a formula to calculate the number of lone pairs on the central atom of a molecule. The formula involves subtracting 8 times the number of atoms attached to the central atom from the total valence electrons, then dividing by 2. The tutorial provides examples with sulfur dioxide, nitrogen trifluoride, xenon tetrafluoride, and the tribromide ion, demonstrating how to apply the formula and draw Lewis structures. It emphasizes the octet rule and the possibility of expanded octets for certain atoms.

What is the formula to calculate the number of lone pairs on the central atom of a molecule?

• Total valence electrons minus 8n divided by 2

• Total valence electrons plus 8n divided by 2

• Total valence electrons minus 4n divided by 2

• Total valence electrons plus 4n divided by 2

In the sulfur dioxide example, how many valence electrons are present in total?

• 22

• 20

• 16

• 18

For sulfur dioxide, what is the value of n, the number of atoms attached to the central atom?

• 4

• 1

• 2

• 3

In the nitrogen trifluoride example, how many lone pairs are on the central nitrogen atom?

• 2

• 3

• 0

• 1

How many valence electrons are there in total for nitrogen trifluoride?

• 30

• 24

• 26

• 28

What is the molecular geometry of xenon tetrafluoride?

• Octahedral

• Trigonal bipyramidal

• Square planar

• Tetrahedral

How many lone pairs are present on the central xenon atom in xenon tetrafluoride?

• 2

• 1

• 3

• 4

In the tribromide ion example, how many lone pairs are on the central bromine atom?

• 1

• 4

• 2

• 3

What is the total number of valence electrons in the tribromide ion?

• 21

• 20

• 23

• 22

Which of the following elements can have an expanded octet?

• Oxygen

• Hydrogen

• Nitrogen

• Bromine