Explain each of the following occurrences using principles of intermodular and i

Question

Explain each of the following occurrences using principles of intermodular and intramolecular forces. Make sure that your answers include details about all species mentioned in the question. At 1.0 atm and 25.0 degree C Cl_2 exists as a gas and I_2 exists as a solid. The melting point of SiO_2 is much higher than the melting point of NF_3. A metal crystallizes with a face-centered cubic lattice. The edge of the unit cell a 408 pm. Calculate the radius of the metal atom. Which of the following structures has the largest standard heat of vaporization DeltaH^0_vap value? Justify your answer.

Explanation / Answer

A) (I)

At 1.0 atm and 25 C, Cl2 exist as gas and I2 as solid.

The molecules of elements attract each other through intermolecular forces of attraction, which is london dispersion force in this case as both are non polar molecules. In smaller molecules, electron cloud around the atom is held tightly by the nucleus, so distortion of cloud is very less. More is distortion, more will be intermolecular force of attraction. So, due to lesser distortion in chlorine atoms as compared to iodine, intermolecular forces of attraction are less in chlorine than iodine.

Hence, Chlorine molecule exists as liquid and iodone molecule exists as solid.

A (II).

SiO2 is a covalent network solid. Whereas, in NF3, the molecules are held togather by dipole-dipole forces. Since, colavent forces of attraction > dipole dipole force of attraction, SiO2 has higher MP than NF3.

B. We are given side of unit cube in FCC lattice(a) = 408 pm.

Since in FCC, radius of metal atom = a/(2 *2),

So, Diameter = a/(2) = 408/1.414 = 288.5 pm (Ans)

(C)

Structure I is pentane and Structure II is propane. Since, in hydrocarbons, intermolecular force of attractions are directly proportional to their molecular weights, and MW of pentane > MW of propane.

Hence, Heat of vap in Structure I > Structure II. (Ans)

PS: Fact: Heat of Vap of propane =15.7 Kj/mol & Heat of Vap of pentane = 26.2 Kj/mol

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