14. 14. Which of these statements correctly describes the use of formal charge i

Question

14. 14. Which of these statements correctly describes the use of formal charge in choosing between possible Lewis structures to describe a molecule? I. Formal charge on all the atoms should be zero, or at least the smallest possible value. II. he sum of the formal charges on all the atoms should equal the charge on the molecule or ion. Ill. The formal charge on an atom is not affected by the of the atom. nitrogen will containing nitrogen and oxygen, the Lewis structures with a charge on the IV. contribute the most to the description of the bonding. a. II and III only d. III and IV only b. II and IV only e. I and II only c. I and III only

Explanation / Answer

(14) Formal charge is the charge an atom has in the Lewis structure and it's calculated by the following formula:

Formal charge = (number of valence electrons) - ( number of nonbonding electrons) - 1/2 ( number of bonding electrons)

In a Lewis structure, atoms with no formal charges are preferred over formal charges.The sum of the formal charges must be zero in a neutral a molecule. For a polyatomic ion the formal charges must add up to the charge of the ion.

For this reason, statements I and II are correct.

Formal charge depends on the number of bonding electrons and electronegativity values. An atom with high electronegativity attracts more electrons. Oxygen is more electronegative than nitrogen. Therefore, negative formal charge on nitrogen atom is not preferred.

For this reason, statements III and IV are incorrect.

(Ans) (e) I and II only

(15) Vapor pressure increases with decrease in boiling point because when a compound boils at lower temperature its vapor pressure increases. Longer chain molecules have higher boiling points. For this reason, the compound with the least number of C atoms has the lowest boiling point and the highest vapor pressure. The compound is C4H10.

(Ans) (b) C4H10

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