Question
Which of the following Lewis diagrams represents a molecule that is polar?
▶️Answer/Explanation
Ans:C
In the \(CH_2Cl_2\) molecule, the H and Cl atoms are in a tetrahedral arrangement around the central C atom. The two electronegative chlorine atoms create a partial negative charge on their side of the carbon atom, leaving a partial positive charge on the opposite (hydrogen) side of the carbon atom. This separation of charge constitutes a dipole, and the molecule is polar.
Question
Which of the following correctly compares the strength of the two carbon-to-carbon bonds in the molecule represented in the Lewis diagram shown above?
▶️Answer/Explanation
Ans:A
Double bonds between two atoms are always stronger than single bonds between those same two atoms because in a double bond there are more electrons between the two positive nuclei of the atoms, which results in a stronger bond.
Question
Based on the Lewis diagram for \(NH_3\) , shown above, the H-N-H bond angle is closest to which of the following?
A 60°
B 90°
C 109.5°
D 120°
▶️Answer/Explanation
Ans:C
With four electron domains around the central N atom, their geometry is tetrahedral (which minimizes repulsion among the four electron pairs). The tetrahedral angle is 109.5°; therefore, the H-N-H bond angle is approximately 109.5°.
Question
The structural formula of the glycinium cation is shown above. Arrows indicate the \( pK_{ a}\) values for the labile protons in the molecule.
What is the approximate H-O-C bond angle in the glycinium cation?
(A) 180°
(B) 120°
(C) 105°
(D) 90°
▶️Answer/Explanation
Ans:A
The structural formula of the glycinium cation is shown above. Arrows indicate the \( pK_{ a}\) values for the labile protons in the molecule.
Question
Which of the following is true about the geometry of the glycinium cation?
(A) The leftmost C atom and all the atoms directly bonded to it lie in the same plane.
(B) Both C atoms and both O atoms lie in the same plane.
(C) The N-C-C bond angle is 180°.
(D) The geometry around the N atom is planar.
▶️Answer/Explanation
Ans:C