Question 1

Which of the following statements best explains why the geometry of methane ($$CH_4) is $$tetrahedral rather than planar?

Accepted Answer

The repulsion between the bonding pairs of electrons is minimized when the bond angles are $$109.5^\circ$$, resulting in a tetrahedral geometry.

Question 2

When drawing the Lewis structure for $$PCl_3$$, how many valence electrons are used in total, and how many are left after forming single bonds between phosphorus and each chlorine?

Accepted Answer

$$26$$ valence electrons in total; $$20$$ left after forming three single bonds.

Question 3

Which of the following is the correct formal charge on each atom in the best Lewis structure for the cyanate ion ($$NCO^-$$)?

Accepted Answer

N: $$-1$$, C: $$0$$, O: $$0$$

Question 4

Ozone ($$O_3) is $$best described by which of the following statements regarding its bonding and structure?

Accepted Answer

Ozone has two bonds of equal length due to resonance, with each oxygen atom having a charge of $$-1/2.$$

Question 5

Which of the following best describes the concept of resonance in molecules such as benzene ($$C_6H_6$$)?

Accepted Answer

Resonance means that the actual structure is a hybrid of multiple possible Lewis structures, with delocalized electrons.

Question 6

According to VSEPR theory, what is the electron-domain geometry and the molecular geometry of $$NH_3 ($$ammonia)?

Accepted Answer

Electron-domain geometry: tetrahedral; Molecular geometry: trigonal pyramidal

Question 7

Which hybridization is associated with a linear geometry, and how many hybrid orbitals are formed?

Accepted Answer

$$sp$$ hybridization; 2 hybrid orbitals

Question 8

In the context of valence-bond theory, which statement correctly distinguishes between sigma ($$\sigma) $$and pi ($$\pi) $$bonds?

Accepted Answer

$$\sigma$$ bonds have electron density along the internuclear axis, while $$\pi$$ bonds have electron density above and below the axis.

Question 9

Which of the following molecules contains both $$\sigma$$ and $$\pi$$ bonds?

Accepted Answer

$$C_2H_4 ($$ethene)

Question 10

A molecule has three electron domains around its central atom. What is its predicted electron-domain geometry and ideal bond angle?

Accepted Answer

Trigonal planar; $$120^\circ$$

Question 11

Which of the following best explains why the retinal molecule changes shape upon absorption of visible light, as related to human vision?

Accepted Answer

Absorption of visible-light photons provides energy to break a $$C-C$$ bond, leading to a change in molecular geometry.

Question 12

Which of the following is the correct sequence of steps for drawing a Lewis structure for a neutral covalent molecule?

Accepted Answer

Sum valence electrons, choose central atom, connect outer atoms with single bonds, complete octets on outer atoms, complete octet on central atom.

Question 13

Which of the following molecules or ions is best described as having delocalized $$\pi$$ electrons?

Accepted Answer

$$C_6H_6 ($$benzene)

Question 14

Which of the following statements about formal charge is correct?

Accepted Answer

The best Lewis structure is the one with the fewest formal charges and places negative formal charges on the most electronegative atoms.

Question 15

Which hybridization and geometry are expected for the central atom in $$BF_3$$?

Accepted Answer

$$sp^2$$ hybridization; trigonal planar geometry

Question 16

A double bond between two carbon atoms consists of which combination of bonds?

Accepted Answer

One $$\sigma$$ bond and one $$\pi$$ bond

Question 17

Which of the following real-world examples best illustrates the importance of molecular geometry in biological function?

Accepted Answer

The change in geometry of retinal upon absorption of light triggers the visual process in the human eye.

Question 18

Which of the following statements about $$sp^3$$ hybridization is correct?

Accepted Answer

$$sp^3$$ hybridization involves mixing one s and three p orbitals to form four equivalent hybrid orbitals.

Question 19

Which of the following best describes the bonding in $$H_2 ($$hydrogen gas) according to valence-bond theory?

Accepted Answer

A $$\sigma$$ bond is formed by the overlap of two $$1s$$ atomic orbitals.

Molecular Geometry and Bonding Theories: Lewis Structures, Formal Charges, and Resonance

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