Q: Which of the following is the correct formula for calculating the formal charge on an atom?

$$\text{Formal charge} = \text{number of valence electrons} - (\text{number of nonbonding electrons} + \frac{1}{2} \times \text{number of bonding electrons})$$

Question 1

Which of the following statements about hydrogen in Lewis structures is correct?

Accepted Answer

Hydrogen can only form one bond and cannot have more than two electrons.

Question 2

Which of the following elements can have an expanded octet in a Lewis structure?

Accepted Answer

Sulfur

Question 3

What is the formal charge on the central atom in the best Lewis structure for $$\ce{SO_3$}$$?

Accepted Answer

$$0$$

Question 4

Which of the following molecules or ions has resonance structures?

Accepted Answer

$$\ce{NO_3$^-}$$

Question 5

Which of the following is the correct formula for calculating the formal charge on an atom?

Accepted Answer

$$	ext{Formal charge} = 	ext{number of valence electrons} - (	ext{number of nonbonding electrons} + \frac{1}{2} 	imes 	ext{number of bonding electrons})$$

Question 6

Which of the following best explains why $$\ce{BF_3$}$$ does not obey the octet rule?

Accepted Answer

Boron has only three valence electrons and forms three bonds, resulting in only six electrons around it.

Question 7

Which of the following ions has the greatest number of resonance structures?

Accepted Answer

$$\ce{SO_4$^{2-}}$$

Question 8

Which of the following statements about resonance is correct?

Accepted Answer

The actual structure of a molecule with resonance is a hybrid of all possible resonance structures.

Question 9

Which of the following bonds is expected to have the highest bond energy?

Accepted Answer

$$\ce{C#C}$$

Question 10

Given the following reaction: $$\ce{CH_4$ + 2O_2 -\u003e CO_2$ + 2H_2O}$$, which of the following steps is NOT part of using bond energies to estimate $$\Delta H_{rxn}$$?

Accepted Answer

Multiply the bond energies of all bonds by the atomic masses of the elements involved.

Question 11

Which of the following molecules is most likely to have a polar covalent bond?

Accepted Answer

$$\ce{HCl}$$

Question 12

Which of the following is a correct statement about the relationship between bond order and bond length?

Accepted Answer

As bond order increases, bond length decreases.

Question 13

Which of the following is the best Lewis structure for the cyanide ion, $$\ce{CN^-}$$?

Accepted Answer

A structure with a triple bond between C and N, and a lone pair on each atom.

Question 14

Which of the following is a valid exception to the octet rule?

Accepted Answer

Boron in $$\ce{BF_3$}$$

Question 15

Which of the following best describes the bond character in $$\ce{NaCl}$$?

Accepted Answer

Ionic

Question 16

What is the bond order of the nitrogen-oxygen bond in the nitrate ion, $$\ce{NO_3$^-}$$?

Accepted Answer

$$1.5$$

Question 17

Which of the following is the correct order of steps for drawing a Lewis structure?

Accepted Answer

Count valence electrons, connect atoms with single bonds, complete octets, assign formal charges

Question 18

Which of the following molecules or ions is most likely to have a central atom with a negative formal charge in its best Lewis structure?

Accepted Answer

$$\ce{CO_3$^{2-}}$$

Question 19

Which of the following is true about the use of formal charges in determining the best Lewis structure?

Accepted Answer

The best Lewis structure minimizes formal charges and places negative charges on the most electronegative atoms.

Question 20

Which of the following is a real-world application of resonance structures?

Accepted Answer

Describing the delocalized electrons in the nitrate ion, $$\ce{NO_3$^-}$$, which affects its reactivity and stability

Chapter 7 Student Notes

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