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

$$\text{Formal charge} = \text{Number of valence electrons} - (\text{All unshared electrons} + \frac{1}{2} \text{All shared electrons})$$

Question 1

Which of the following statements best explains why the bond angle in water ($$\ce{H2O}) is $$less than the ideal tetrahedral angle?

Accepted Answer

The two lone pairs on oxygen repel the bonding pairs more strongly, compressing the bond angle to about $$104.5^\circ.$$

Question 2

Which of the following molecules is nonpolar despite having polar bonds?

Accepted Answer

$$\ce{CO2}$$

Question 3

What is the formal charge on the central carbon atom in the acetate ion ($$\ce{CH3COO^-}$$)?

Accepted Answer

$$0$$

Question 4

Which of the following best describes the hybridization and geometry of the nitrogen atom in ammonia ($$\ce{NH3}$$)?

Accepted Answer

$$sp^3$$ hybridized, trigonal pyramidal

Question 5

Which of the following bonds is the most polar according to the Pauling electronegativity scale?

Accepted Answer

$$\ce{H-F}$$

Question 6

Which of the following is a correct Lewis structure for carbon dioxide ($$\ce{CO2}$$)?

Accepted Answer

O=C=O, with each O atom having two lone pairs

Question 7

Which of the following functional groups is present in both acetone and formaldehyde?

Accepted Answer

Carbonyl group ($$C=O)$$

Question 8

Which of the following molecules has a bond angle closest to $$120^\circ$$?

Accepted Answer

$$\ce{C2H4} ($$ethylene)

Question 9

Which of the following statements about resonance structures is FALSE?

Accepted Answer

The actual molecule is best represented by the most stable resonance structure only.

Question 10

Which of the following best explains why fluorine is the most electronegative element?

Accepted Answer

It has the highest effective nuclear charge and the smallest atomic radius in its period.

Question 11

Which of the following molecules is expected to have a net dipole moment ($$\mu \u003e 0$$)?

Accepted Answer

$$\ce{CH2Cl2}$$

Question 12

What is the correct ground-state electron configuration for silicon ($$Z=14$$)?

Accepted Answer

$$1s^2$$ $$2s^2$$ $$2p^6$$ $$3s^2$$ $$3p^2$$

Question 13

Which of the following best describes the bonding in methane ($$\ce{CH4}$$)?

Accepted Answer

Four $$sp^3$$ hybrid orbitals on carbon overlap with four $$1s$$ orbitals on hydrogen to form four sigma bonds.

Question 14

Which of the following is the correct condensed structural formula for a secondary amine with the formula $$\ce{C4H11N}$$?

Accepted Answer

$$\ce{CH3CH2NHCH3}$$

Question 15

Which of the following best describes the difference between a ketone and an aldehyde?

Accepted Answer

A ketone has a carbonyl group bonded to two carbons, while an aldehyde has a carbonyl group bonded to at least one hydrogen.

Question 16

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

Accepted Answer

$$	ext{Formal charge} = 	ext{Number of valence electrons} - (	ext{All unshared electrons} + \frac{1}{2} 	ext{All shared electrons})$$

Question 17

Which of the following molecules contains a dative (coordinate covalent) bond?

Accepted Answer

$$\ce{H3N \rightarrow BF3}$$

Question 18

Which of the following best explains why $$\ce{CH4}$$, $$\ce{NH3}$$, and $$\ce{H2O}$$ have different bond angles, even though all have central atoms with $$sp^3$$ hybridization?

Accepted Answer

The number of lone pairs on the central atom increases from $$\ce{CH4} to$$ $$\ce{H2O}$$, increasing electron pair repulsion and decreasing bond angles.

Question 19

Which of the following is a valid resonance structure for the nitrite ion ($$\ce{NO2^-}$$)?

Accepted Answer

Both oxygen atoms can have a negative charge in different resonance forms.

Covalent Bonding and Shapes of Molecules: Foundations of Organic Chemistry

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