Question

Consider the following melting point data:

$$\begin{gathered} Compound NaCl MgC{l}_2 AlC{l}_3 SiC{l}_4 PC{l}_3 SC{l}_2 C{l}_2\backslash \mathrm{hfill} \\ mp\left({}^{\circ }C\right) 801 708 190 -70 -91 -78 -101\backslash \mathrm{hfill} \\ Compound NaF Mg{F}_2 Al{F}_3 Si{F}_4 P{F}_5 S{F}_6 F_2\backslash \mathrm{hfill} \\ mp\left({}^{\circ }C\right) 997 1396 1040 -90 -84 -56 -220\backslash \mathrm{hfill} \end{gathered}$$

Account for the trends in melting points in terms of interparticle

forces.

Short answer

Along the period from left to right, the atomic radius decreases, the covalent nature increases, and the ionic character decreases. Due to this decrease in the ionic character, the melting point also decreases.

Step-by-step solution

Ionic character

Along the period from left to right, the atomic radius decreases, leading to the decrease in electrons losing the capacity of atoms which is nothing but a decrease in ionic character. The covalent nature of the atoms increases.

 Step2: The given data

From the given data, it is clear that the chlorides and fluorides of the second-period elements show a gradual decrease in their melting points due to the decrease in their ionic character.