Questions: States of Matter Predicting the relative boiling points of pure substances 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. substance chemical formula or Lewis structure boiling point A Co B H-C≡C-H C H2 D O=C=O

Solution Steps

To predict the boiling points, we need to consider the types of intermolecular forces present in each substance. The stronger the intermolecular forces, the higher the boiling point.

• A (Co): Cobalt is a metal, and its boiling point is determined by metallic bonding, which is generally strong.
• B ($\ce{H-C#C-H}$): This is acetylene, a small nonpolar molecule with weak London dispersion forces.
• C ($\ce{H2}$): Hydrogen is a nonpolar molecule with very weak London dispersion forces.
• D ($\ce{O=C=O}$): Carbon dioxide is a linear nonpolar molecule with weak London dispersion forces.

• Metallic Bonding (Co): Typically results in high boiling points due to strong metallic bonds.
• London Dispersion Forces (Acetylene, $\ce{H2}$, $\ce{CO2}$): These are weaker than metallic bonds. Among these, larger molecules or those with more electrons generally have stronger dispersion forces.

• Cobalt (Co): As a metal, it will have the highest boiling point due to strong metallic bonds.
• Acetylene ($\ce{H-C#C-H}$): Although nonpolar, it is larger than $\ce{H2}$ and $\ce{CO2}$, leading to stronger dispersion forces.
• Carbon Dioxide ($\ce{O=C=O}$): Larger than $\ce{H2}$, so it will have a higher boiling point than hydrogen.
• Hydrogen ($\ce{H2}$): The smallest and lightest molecule, with the weakest dispersion forces.

Final Answer