Chapter 18: The Representative Elements

How could you determine experimentally whether the compound ${\mathbf{Ga}}_{\mathbf{2}}{\mathbf{Cl}}_{\mathbf{4}}$contains two gallium(II)ions or one gallium(I)ion and one gallium(III)ion? (Hint: Consider the electron configurations of the three possible ions.)

It takes 15kWh(kilowatt-hours) of electrical energy to produce 1.0 kgof aluminum metal from aluminum oxide by the Hall–Heroult process. Compare this to the energy necessary to melt 1.0 kgof aluminum metal. Why is it economically feasible to recycle aluminum cans? [The enthalpy of fusion for aluminum metal is$\mathbf{10}\mathbf{.}\mathbf{7}\mathbf{kJ}\mathbf{/}\mathbf{mol}\mathbf{(}\mathbf{1}\mathbf{W}\mathbf{=}\mathbf{1}\mathbf{J}\mathbf{/}\mathbf{s}\mathbf{)}$.]

Reference Table 18.5, and give examples of the three types of alkali metal oxides that form. How do they differ?

Why are the tin (IV) halides more volatile than the tin (II) halides?

Beryllium shows some covalent characteristics in some of its compounds, unlike the other alkaline earth halides. Give a possible explanation for this phenomenon.

One reason suggested for the instability of long chains of silicon atoms is that the decomposition involves the transition state shown below:

The activation energy for such a process is $\text{210kJ/mol}$, which is less than either the $\text{Si - Si}$or thebond energy. Why would a similar mechanism not be expected to be very important in the decomposition of long carbon chains?

Many structures of phosphorus- and sulfur-containing compounds are drawn with some $\mathrm{P}=O$and $\mathrm{P}=S$bonds. These bonds are not the typicalbonds we've considered, which involve the overlap of twoorbitals. They result instead from the overlap of a $d$orbital on the phosphorus or sulfur atom with a $p$orbital on oxygen. This type of $\pi$bonding is sometimes used as an explanation for why${\text{H}}_{\text{3}}{\text{PO}}_{\text{3}}$has the first structure below rather than the second:

Draw a picture showing how a$d$orbital and a$p$orbital overlap to form abond.

The${\text{N}}_{\text{2}}\text{O}$molecule is linear and polar.

1. On the basis of this experimental evidence, which arrangement, NNO or$\text{NON}$, is correct? Explain your answer.
2. On the basis of your answer in part a, write the Lewis structure of${\text{N}}_{\text{2}}\text{O}$(including resonance forms). Give the formal charge on each atom and the hybridization of the central atom.
3. How would the multiple bonding in

$\mathit{N}\equiv \mathit{N}-\stackrel{..}{\mathit{O}}\text{:}$

be described in terms of orbitals?

Although nitrogen$\left({\text{NF}}_{\text{3}}\right)$is a thermally stable compound, nitrogen triiodide$\left({\text{NF}}_{\text{3}}\right)$is known to be a highly explosive material.${\text{NI}}_{\text{3}}$can be synthesized according to the equation

$\text{BN(s) + 3IF(g)}\to {\text{BF}}_{\text{3}}{\text{(g) + NI}}_{\text{3}}\text{(g)}$

1. What is the enthalpy of formation for ${\text{NI}}_{\text{3}}\text{(s)}$ given the enthalpy of $\left(\text{-307kJ}\right)$ and the enthalpies of formation for BN$\left(s\right)(-254kJ/mol),IF\left(g\right)$$(-96kJ/mol)$ , and ${\text{BF}}_3\left(\text{g}\right)\left(\text{-1136kJ/mol}\right)$ ?
2. It is reported that when the synthesis of ${\text{NI}}_{\text{3}}$is conducted using 4 moles of IF for every 1 mole of BN, one of the by-products isolated is ${\left[{\text{IF}}_{\text{2}}\right]}^{\text{+}}{\left[{\text{BF}}_{\text{4}}\right]}^{\text{-}}$

What are the molecular geometries of the species in this by-product? What are the hybridizations of the central atoms in each species in the by-product?

Halogens form a variety of covalent compounds with each other. For example, chlorine and fluorine form the compounds${\text{ClF,ClF}}_{\text{3}}$, and${\text{ClF}}_{\text{5}}$. Predict the molecular structure (including bond angles) for each of these three compounds. Would you expect${\text{FCl}}_{\text{3}}$to be a stable compound? Explain.