Question

exam 2 fall 2025 your initials nt (ii) (5 points) which of the following has the longest bond? the number in parentheses is the bond energy. c - c (348 kj/mol) c - f (453 kj/mol) c - h (411 kj/mol) c - cl (339 kj/mol) c - o (358 kj/mol) (iii) (5 points) which of the following is the best structure for n₂o? a. :o - n≡n: b. o = n = n :o - n≡n: c. d. n = o = n e. n - o - n (iv) (5 points) which of the following is most likely a polar covalent bond? na - cl h - h c - n k - f ca - o (v) (5 points) in which of the following molecules does the central atom have an expanded octet? n₂o pcl₅ bef₂ asf₃ no₂ (vi) (5 points) what is the formal charge of each atom (from left to right) in the following resonance structure of sn₂? :s - n≡n: 0, 0, 0 -1, +1, 0 -2, +1, 0 -2, -1, +1 -1, -1, +1 (vii) (5 points) which of the following (figure 2) is a p orbital? circle all that apply.

Explanation:

Step1: Recall bond - energy and bond - length relationship

Bond energy is inversely proportional to bond length. Lower bond energy means longer bond length.

Step2: Compare bond energies

Given bond energies: C - C (348 kJ/mol), C - F (453 kJ/mol), C - H (411 kJ/mol), C - Cl (339 kJ/mol), C - O (358 kJ/mol). The lowest bond energy is 339 kJ/mol for C - Cl. So C - Cl has the longest bond.

Step1: Consider formal - charges and resonance in $N_2O$

The best Lewis structure minimizes formal charges. For $N_2O$, the structure with the most stable distribution of electrons and lowest formal - charges is O=N=N (structure b). In this structure, the formal charges are minimized compared to other possible structures.

Step1: Recall electronegativity and polar - covalent bonds

A polar covalent bond occurs when there is a significant difference in electronegativity between two atoms. Na - Cl and K - F and Ca - O are ionic bonds. H - H is a non - polar covalent bond. For C - N, there is a moderate electronegativity difference, making it a polar covalent bond.

Step1: Understand the concept of an expanded octet

An expanded octet occurs when an atom has more than 8 valence electrons. In $N_2O$, N and O follow the octet rule. In $BeF_2$, Be has an incomplete octet. In $AsF_3$, As has 8 valence electrons. In $NO_2$, N and O follow the octet rule or have a resonance structure with an octet. In $PCl_5$, P has 10 valence electrons (an expanded octet).

Answer:

C - Cl (339 kJ/mol)