Consider the lattice energies of the following Group 2A compounds: BeH₂, 3205 kJ/mol; MgH₂, 2791 kJ/mol; CaH₂, 2410 kJ/mol; SrH₂, 2250 kJ/mol; BaH₂, 2121 kJ/mol. (a) What is the oxidation number of H in these compounds?

The ionic compound CaO crystallizes with the same structure as sodium chloride (Figure 8.3). (a) In this structure, how many O2- are in contact with each Ca2+ ion (Hint: Remember the pattern of ions shown in Figure 8.3 repeats over and over again in all three directions.)

Construct a Born–Haber cycle for the formation of the hypothetical compound NaCl₂, where the sodium ion has a 2⁺ charge (the second ionization energy for sodium is given in Table 7.2). (a) How large would the lattice energy need to be for the formation of NaCl₂ to be exothermic?

Consider the collection of nonmetallic elements O, P, Te, I, and B. (a) Which two would form the most polar single bond?

Consider the collection of nonmetallic elements O, P, Te, I, and B. (b) Which two would form the longest single bond?

The substance chlorine monoxide, ClO(g), is important in atmospheric processes that lead to depletion of the ozone layer. The ClO molecule has an experimental dipole moment of 1.24 D, and the Cl — O bond length is 160 pm. (b) Based on the electronegativities of the elements, which atom would you expect to have a partial negative charge in the ClO molecule?

(b) Using these partial charges and the atomic radii given in Figure 7.8, estimate the dipole moment of the molecule.

(c) The measured dipole moment of BrCl is 0.57 D. If you assume the bond length in BrCl is the sum of the atomic radii, what are the partial charges on the atoms in BrCl using the experimental dipole moment?

A major challenge in implementing the 'hydrogen economy' is finding a safe, lightweight, and compact way of storing hydrogen for use as a fuel. The hydrides of light metals are attractive for hydrogen storage because they can store a high weight percentage of hydrogen in a small volume. For example, NaAlH4 can release 5.6% of its mass as H2 upon decomposing to NaH(s), Al(s), and H2(g). NaAlH4 possesses both covalent bonds, which hold polyatomic anions together, and ionic bonds. (b) Which element in NaAlH4 is the most electronegative? Which one is the least electronegative? Which element in NaAlH4 is the least electronegative?

A major challenge in implementing the 'hydrogen economy' is finding a safe, lightweight, and compact way of storing hydrogen for use as a fuel. The hydrides of light metals are attractive for hydrogen storage because they can store a high weight percentage of hydrogen in a small volume. For example, NaAlH₄ can release 5.6% of its mass as H2 upon decomposing to NaH(s), Al(s), and H₂(g). NaAlH₄ possesses both covalent bonds, which hold polyatomic anions together, and ionic bonds. (c) Based on electronegativity differences, predict the identity of the polyatomic anion. Draw a Lewis structure for this ion.

A major challenge in implementing the 'hydrogen economy' is finding a safe, lightweight, and compact way of storing hydrogen for use as a fuel. The hydrides of light metals are attractive for hydrogen storage because they can store a high weight percentage of hydrogen in a small volume. For example, NaAlH₄ can release 5.6% of its mass as H2 upon decomposing to NaH(s), Al(s), and H₂(g). NaAlH₄ possesses both covalent bonds, which hold polyatomic anions together, and ionic bonds. (d) What is the formal charge on hydrogen in the polyatomic ion?

Structures A, B, and C show the connectivity of the atoms in three different molecules that are isomers of C3H4O. By completing the Lewis structures of these molecules, complete the information in the following table:

Isomer A Isomer B Isomer C

Number of single bonds

Number of double bonds

Number of triple bonds

Number of nonbonding pairs

The triiodide ion, I3-, exists, whereas the corresponding ion with fluorine, F3-, does not. The I3- ion has a linear structure in which two outer I atoms are each bonded to a central I atom. Although I3- is a known ion, F3- is not.

c. Which of the following statements about the existence of I3- versus the nonexistence of F3- is or are true?

i. The Lewis structure of I3- shows 12 electrons around the central I atom.

ii. Elements from the second row of the periodic table generally do not form hypervalent molecules and ions.

iii. An I atom can form a hypervalent molecule or ion more readily than an F atom because of the larger size of the I atom.

The hypochlorite ion, ClO^-, is the active ingredient in bleach. The perchlorate ion, ClO₄^-, is a main component of rocket propellants. Draw Lewis structures for both ions. (b) What is the formal charge of Cl in the perchlorate ion, assuming the Cl—O bonds are all single bonds?

The following three Lewis structures can be drawn for N2O:

(a) Using formal charges, which of these three resonance forms is likely to be the most important?

The following three Lewis structures can be drawn for N2O:

(b) The N—N bond length in N2O is 1.12 Å, slightly longer than a typical N ≡N bond; and the N— O bond length is 1.19 Å, slightly shorter than a typical N ═O bond (see Table 8.4). Based on these data, which resonance structure best represents N2O?

Mothballs are composed of naphthalene, C₁₀H₈, a molecule that consists of two six-membered rings of carbon fused along an edge, as shown in this incomplete Lewis structure:(a) Draw all of the resonance structures of naphthalene. How many are there?

Mothballs are composed of naphthalene, C₁₀H₈, a molecule that consists of two six-membered rings of carbon fused along an edge, as shown in this incomplete Lewis structure:

(b) Do you expect the C—C bond lengths in the molecule to be similar to those of C—C single bonds, C ═ C double bonds, or intermediate between C—C single and C ═ C double bonds?

Mothballs are composed of naphthalene, C₁₀H₈, a molecule that consists of two six-membered rings of carbon fused along an edge, as shown in this incomplete Lewis structure:

(c) Not all of the C—C bond lengths in naphthalene are equivalent. Based on your resonance structures, how many C—C bonds in the molecule do you expect to be shorter than the others?

a. Triazine, C3H3N3, is like benzene except that in triazine every other C—H group is replaced by a nitrogen atom. Draw the Lewis structure(s) for the triazine molecule.

Ortho-Dichlorobenzene, C₆H₄Cl₂, is obtained when two of the adjacent hydrogen atoms in benzene are replaced with Cl atoms. A skeleton of the molecule is shown here. (a) Complete a Lewis structure for the molecule using bonds and electron pairs as needed.

Ortho-Dichlorobenzene, C₆H₄Cl₂, is obtained when two of the adjacent hydrogen atoms in benzene are replaced with Cl atoms. A skeleton of the molecule is shown here. (b) Are there any resonance structures for the molecule? If so, sketch them.

Two compounds are isomers if they have the same chemical formula but different arrangements of atoms. Use Table 8.3 to estimate H for each of the following gas-phase isomerization reactions and indicate which isomer has the lower enthalpy. (d) Methyl isocyanide → Acetonitrile

The electron affinity of oxygen is -141 kJ/mol, corresponding to the reaction O(g) + e^- → O^-(g). The lattice energy of K₂O(s) is 2238 kJ/mol. Use these data along with data in Appendix C and Figure 7.11 to calculate the 'second electron affinity' of oxygen, corresponding to the reaction O^-(g) + e^- → O^2-(g)