Question

rank the elements or compounds in the table below in decreasing order of their boiling points. that is, choose 1 next to the substance with the highest boiling point, choose 2 next to the substance with the next highest boiling point, and so on. table with substance a: cacl₂, b: lewis structure (o=n-cl with lone pairs), c: cl₂, d: lewis structure (c=c with four cl atoms, each with lone pairs), and boiling point selection dropdowns (select ↓) for each substance

Explanation:

Step1: Identify Bond Types and Forces

• Substance A (\(CaCl_2\)): Ionic compound (metal + non - metal). Ionic bonds are strong electrostatic attractions between ions.
• Substance B (Lewis structure: \(O = N - Cl\)): Covalent compound, polar (due to electronegativity differences in \(O - N\) and \(N - Cl\) bonds), so has dipole - dipole interactions and London dispersion forces.
• Substance C (\(Cl_2\)): Diatomic non - metal, non - polar covalent, only London dispersion forces.
• Substance D (Lewis structure: \(C_2Cl_4\)): Covalent compound, non - polar (symmetrical structure), only London dispersion forces. But it has a larger molar mass than \(Cl_2\).

Step2: Relate Forces to Boiling Points

• Ionic compounds (like \(CaCl_2\)) have much stronger intermolecular forces (ionic bonds) than covalent compounds (which have dipole - dipole or London dispersion forces). So \(CaCl_2\) has the highest boiling point (rank 1).
• Among covalent compounds:
• Substance B is polar (dipole - dipole + London dispersion), Substance D is non - polar (London dispersion) but has a larger molar mass than Substance C (\(Cl_2\)). Molar mass affects London dispersion forces (larger molar mass → stronger London dispersion). Also, dipole - dipole forces are stronger than London dispersion forces of similar molar mass.
• Molar mass of \(Cl_2\): \(M(Cl_2)=2\times35.45 = 70.9\space g/mol\)
• Molar mass of \(C_2Cl_4\): \(M(C_2Cl_4)=2\times12.01+4\times35.45=24.02 + 141.8 = 165.82\space g/mol\)
• Substance B: Let's calculate molar mass. \(O = 16.00\), \(N = 14.01\), \(Cl = 35.45\). \(M(ONCl)=16.00 + 14.01+35.45 = 65.46\space g/mol\)
• The strength of intermolecular forces: Ionic (\(CaCl_2\)) > Dipole - dipole (\(ONCl\)) > London dispersion (\(C_2Cl_4\) > \(Cl_2\)) because \(C_2Cl_4\) has a larger molar mass than \(Cl_2\), so its London dispersion forces are stronger.

So the order of boiling points from highest to lowest is: \(CaCl_2\) (A) > \(ONCl\) (B) > \(C_2Cl_4\) (D) > \(Cl_2\) (C)

Answer:

1. A (\(CaCl_2\))
2. B (\(ONCl\))
3. D (\(C_2Cl_4\))
4. C (\(Cl_2\))