Question

step 1: draw the following lewis structures
nf₃
f₂
step 2: list the intermolecular forces (imfs) present for each
nf₃:
f₂:
step 3: evaluating physical properties
which molecule will have a higher boiling point? explain why. (use imfs and energy to justify your answer)
which molecule will have a higher melting point? explain why. (use imfs and energy to justify your answer)

Explanation:

Step 1: Draw Lewis Structures

• For \( \text{NF}_3 \): Nitrogen (N) is the central atom. N has 5 valence electrons, and each F has 7. N forms single bonds with 3 F atoms, using 3 electrons (1 per bond), leaving 1 lone pair on N. Each F has 3 lone pairs. The Lewis structure is as shown (with N in the center, single bonds to three F, each F with 3 lone pairs, N with 1 lone pair).
• For \( \text{F}_2 \): Two F atoms form a single bond. Each F has 3 lone pairs. The Lewis structure is \( \text{:F - F:} \) with 3 lone pairs on each F.

Step 2: List Intermolecular Forces (IMFs)

• \( \text{NF}_3 \): It is a polar molecule (due to the trigonal pyramidal shape and electronegativity difference between N and F). So, it has London dispersion forces (LDF) and dipole - dipole interactions.
• \( \text{F}_2 \): It is a non - polar molecule (diatomic, same atoms). So, it only has London dispersion forces (LDF).

Step 3: Evaluate Boiling Point

• Boiling point depends on the strength of IMFs. Stronger IMFs require more energy to break. \( \text{NF}_3 \) has dipole - dipole interactions in addition to LDF, while \( \text{F}_2 \) only has LDF. Dipole - dipole interactions are stronger than LDF alone. So, \( \text{NF}_3 \) will have a higher boiling point because it has stronger intermolecular forces (dipole - dipole + LDF vs. only LDF in \( \text{F}_2 \)), requiring more energy to change from liquid to gas.

Step 4: Evaluate Melting Point

• Melting point also depends on IMFs. Similar to boiling point, \( \text{NF}_3 \) has stronger IMFs (dipole - dipole + LDF) compared to \( \text{F}_2 \) (only LDF). So, \( \text{NF}_3 \) will have a higher melting point as more energy is needed to break the intermolecular forces for melting.

Answer:

• Lewis Structures: \( \text{NF}_3 \): N (center) - single bonds to 3 F, N has 1 lone pair, each F has 3 lone pairs; \( \text{F}_2 \): \( \text{:F - F:} \) with 3 lone pairs on each F.
• IMFs: \( \text{NF}_3 \): London dispersion forces, dipole - dipole; \( \text{F}_2 \): London dispersion forces.
• Boiling Point: \( \text{NF}_3 \) (because it has stronger IMFs: dipole - dipole + LDF, requiring more energy to boil).
• Melting Point: \( \text{NF}_3 \) (because it has stronger IMFs: dipole - dipole + LDF, requiring more energy to melt).