$$\text{Formal charge} = \text{Valence electrons} - \text{Number of bonds} - \text{Nonbonding electrons}$$

$$\text{Bond order} = \frac{1}{2}(10 - 6) = 2$$

$$\text{Bond order} = \frac{1}{2}(2 - 2) = 0$$

Question 1

Which of the following statements best describes a covalent bond?

Accepted Answer

A bond in which two atoms share a pair of valence electrons to achieve an octet.

Question 2

How many valence electrons are present in a nitrogen atom, and how are they represented in a Lewis dot structure?

Accepted Answer

Nitrogen has 5 valence electrons, represented as five dots around the symbol N.

Question 3

Which of the following molecules is an example of a compound held together by ionic bonds?

Accepted Answer

NaCl

Question 4

Given the Lewis dot structure for CO$$_2$$, how many bonds are present between the carbon and each oxygen atom?

Accepted Answer

Two double bonds

Question 5

Which of the following is a correct formula for calculating formal charge?

Accepted Answer

$$	ext{Formal charge} = 	ext{Valence electrons} - 	ext{Number of bonds} - 	ext{Nonbonding electrons}$$

Question 6

Which molecule below is an example of an exception to the octet rule due to an incomplete octet?

Accepted Answer

BeF$$_2$$

Question 7

What is the bond order of the diatomic molecule O$$_2$$ according to molecular orbital theory?

Accepted Answer

$$	ext{Bond order} = \frac{1}{2}(10 - 6) = 2$$

Question 8

Which statement best explains why double and triple bonds cannot rotate?

Accepted Answer

Because the pi bonds formed by p-orbital overlap restrict rotation.

Question 9

Which of the following molecules exhibits resonance?

Accepted Answer

O$$_3$$

Question 10

Which element is most likely to exhibit valence shell expansion in its compounds?

Accepted Answer

Sulfur (S)

Question 11

What is the main difference between a line-bond structure and a skeletal formula?

Accepted Answer

A line-bond structure shows all atoms and bonds, while a skeletal formula omits carbon and hydrogen atoms bonded to carbon.

Question 12

Which of the following best describes a molecular orbital formed by constructive interference?

Accepted Answer

A bonding molecular orbital with increased electron density between nuclei.

Question 13

Which molecule below is aromatic?

Accepted Answer

C$$_6H$_6 ($$benzene)

Question 14

Which of the following statements about electronegativity is correct?

Accepted Answer

Electronegativity is the ability of an atom to attract bonding electrons.

Question 15

Which of the following bonds is expected to be the shortest?

Accepted Answer

C=O

Question 16

A molecule has the following Lewis structure: $$\mathrm{H}-\mathrm{N}-\mathrm{H}$$ with a lone pair on N. What is the molecular geometry?

Accepted Answer

Trigonal pyramidal

Question 17

Which of the following is true about delocalized electrons in aromatic compounds?

Accepted Answer

Delocalized electrons are shared among multiple atoms, forming a continuous region of electron density.

Question 18

Which molecule below is most likely to have a polar bond?

Accepted Answer

HF

Question 19

What is the bond order for He$$_2$$ according to molecular orbital theory?

Accepted Answer

$$	ext{Bond order} = \frac{1}{2}(2 - 2) = 0$$

Question 20

Which of the following best explains why benzene is unusually stable?

Accepted Answer

Because its electrons are delocalized over the entire ring, lowering the overall energy.

Lewis Dot Structures and Molecular Orbitals: Foundations of Chemical Bonding

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