Carbon diselenide (CSe_ \(_{2} )\) is a liquid at room temperature. The normal boiling point is \(125^{\circ} \mathrm{C},\) and the melting point is \(-45.5^{\circ} \mathrm{C}\) . Carbon disulfide \(\left(\mathrm{CS}_{2}\right)\) is also a liquid at room temperature with normal boiling and melting points of \(46.5^{\circ} \mathrm{C}\) and \(-111.6^{\circ} \mathrm{C},\) respectively. How do the strengths of the intermolecular forces vary from \(\mathrm{CO}_{2}\) to \(\mathrm{CS}_{2}\) to \(\mathrm{CSe}_{2} ?\) Explain.

We first need to identify the types of intermolecular forces in each compound. 1. Carbon dioxide (CO2): Carbon dioxide is a non-polar, linear molecule. This is due to the symmetrical arrangement of the two oxygen atoms around the carbon atom, with oxygen atoms exerting equal and opposite electronegativity forces on the carbon atom. Thus, the only type of intermolecular force present in carbon dioxide is London dispersion forces (LDFs). 2. Carbon disulfide (CS2): Similar to carbon dioxide, carbon disulfide is a linear, non-polar molecule due to the symmetrical arrangement of the sulfur atoms around the carbon atom. Thus, it also experiences London dispersion forces only. 3. Carbon diselenide (CSe2): Just like carbon dioxide and carbon disulfide, carbon diselenide is a linear, non-polar molecule with a symmetrical arrangement. Carbon is surrounded by selenium atoms, which leads to the presence of London dispersion forces.

Now that we have identified the intermolecular forces present in each compound, let's analyze their boiling and melting points to infer which has stronger intermolecular forces. 1. CO2: Carbon dioxide has a boiling point of -56.6°C and a melting point of -78.5°C. 2. CS2: Carbon disulfide has a boiling point of 46.5°C and a melting point of -111.6°C. 3. CSe2: Carbon diselenide has a boiling point of 125°C and a melting point of -45.5°C.

Knowing the boiling and melting points of each compound allows us to infer the strength of intermolecular forces present. A higher boiling or melting point indicates stronger intermolecular forces, while lower boiling and melting points indicate weaker intermolecular forces. The boiling and melting points increase in the following order: CO2 < CS2 < CSe2 This implies that the intermolecular forces increase in the same order: CO2 < CS2 < CSe2

In all three compounds, London dispersion forces are the main intermolecular forces present. London dispersion forces arise due to the presence of instantaneous dipoles and typically become stronger with increasing molecular size or molar mass. As we move from CO2 to CS2 to CSe2, the size and molar mass of the molecules increases because sulfur and selenium atoms are progressively larger and heavier than oxygen atoms. This increase in size and molar mass leads to stronger London dispersion forces in CS2 and CSe2 compared to CO2. Consequently, the intermolecular forces increase in the order mentioned above: CO2 < CS2 < CSe2 Therefore, we can conclude that the strength of intermolecular forces present in these compounds varies as follows: CO2 has the weakest intermolecular forces, CS2 has stronger intermolecular forces, and CSe2 possesses the strongest intermolecular forces. The differences in the strengths of the intermolecular forces are the reason behind the observed differences in boiling and melting points of these compounds.