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Chapter 12: Problem 103

Selected chlorides have the following melting points: NaCl \(\left(801^{\circ} \mathrm{C}\right), \mathrm{MgCl}_{2}\left(714^{\circ} \mathrm{C}\right), \mathrm{PCl}_{3}\left(-94^{\circ} \mathrm{C}\right), \mathrm{SCl}_{2}\left(-121^{\circ} \mathrm{C}\right)\) $$ \begin{array}{l}{\text { (a) For each compound, indicate what type its solid }} \\ {\text { form is (molecular, metallic, ionic, or covalent-network). }} \\\ {\text { (b) Predict which of the following compounds has a }} \\ {\text { higher melting point: } \mathrm{CaCl}_{2} \text { or } \mathrm{SiCl}_{4} \text { . }}\end{array} $$

Short Answer

Expert verified
The types of solids for the given compounds are as follows: \(NaCl\) and \(MgCl_2\) are ionic solids, while \(PCl_3\) and \(SCl_2\) are molecular solids. Comparing the melting points of \(CaCl_2\) and \(SiCl_4\), since \(CaCl_2\) forms a stronger ionic bond, it is predicted to have a higher melting point than \(SiCl_4\), which has a covalent bond.

Step by step solution

01

NaCl - Sodium Chloride

Na is a metal (alkali metal in group 1) and Cl is a non-metal (halogen in group 17), so the bond between them is ionic. Thus, NaCl is an ionic solid.
02

MgCl2 - Magnesium Chloride

Mg is a metal (alkaline earth metal in group 2) and Cl is a non-metal (halogen in group 17), so the bond between them is ionic. Hence, MgCl2 is an ionic solid.
03

PCl3 - Phosphorus Trichloride

P and Cl both are non-metals (P in group 15 and Cl in group 17) which form a covalent bond. As PCl3 consists of discrete molecules instead of a continuous network, it is a molecular solid.
04

SCl2 - Sulfur Dichloride

S and Cl are both non-metals (S in group 16 and Cl in group 17) which form a covalent bond. Like PCl3, SCl2 also consists of discrete molecules, so it is a molecular solid. Step 2: Predicting which compound has a higher melting point between CaCl2 and SiCl4
05

Electronegativity of elements in CaCl2 and SiCl4

Ca is a metal, situated in group 2 (alkaline earth metals). Cl is a non-metal, in group 17 (halogens). Their electronegativity difference is significant, and they form an ionic bond. Si is a metalloid situated in group 14, and Cl is a non-metal in group 17 (halogens). They form a covalent bond due to their closer electronegativities.
06

Comparing melting points of CaCl2 and SiCl4

CaCl2 forms an ionic bond which is stronger than the covalent bond in SiCl4. Ionic solids typically have higher melting points because they require more energy to break the bonds. Therefore, we predict that CaCl2 would have a higher melting point than SiCl4.

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Most popular questions from this chapter

Energy bands are considered continuous due to the large number of closely spaced energy levels. The range of energy levels in a crystal of copper is approximately \(1 \times 10^{-19} \mathrm{J}\) . Assuming equal spacing between levels, the spacing between energy levels may be approximated by dividing the range of energies by the number of atoms in the crystal. (a) How many copper atoms are in a piece of copper metal in the shape of a cube with edge length 0.5 \(\mathrm{mm} ?\) The density of copper is 8.96 \(\mathrm{g} / \mathrm{cm}^{3} .\) (b) Determine the average spacing in J between energy levels in the copper metal in part (a).(c) Is this spacing larger, substantially smaller, or about the same as the 1 \(\times 10^{-18}\) J separation between energy levels in a hydrogen atom?

Aluminum metal crystallizes in a face-centered cubic unit cell. (a) How many aluminum atoms are in a unit cell? (b) What is the coordination number of each aluminum atom? (c) Estimate the length of the unit cell edge, \(a\) , from the atomic radius of aluminum \((1.43 \hat{\mathrm{A}}) .\) (d) Calculate the density of aluminum metal.

What kinds of attractive forces exist between particles (atoms, molecules, or ions) in (a) molecular crystals, (b) covalent-network crystals, (c) ionic crystals, (d) and metallic crystals?

Explain why X rays can be used to measure atomic distances in crystals but visible light cannot be used for this purpose.

At room temperature and pressure RbI crystallizes with the NaCl-type structure. (a) Use ionic radii to predict the length of the cubic unit cell edge. (b) Use this value to estimate the density. (c) At high pressure the structure transforms to one with a CsCl-type structure. (c) Use ionic radii to predict the length of the cubic unit cell edge for the high-pressure form of RbI. (d) Use this value to estimate the density. How does this density compare with the density you calculated in part (b)?
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