The text points out that, for similar types of substances, one with weaker bonds is

In general terms, how does each of the following atomic properties influence the metallic character of the main-group elements in a period? (a) Ionization energy (b) Atomic radius (c) Number of outer electrons (d) Effective nuclear charge

Three solids are represented below. What is the predominant type of intramolecular bonding in each? A B C

What is the relationship between the tendency of a main-group element to form a monatomic ion and its position in the periodic table? In what part of the table are the main-group elements that typically form cations? Anions?

Which member of each pair is more metallic? (a) Na or Cs (b) Mg or Rb (c) As or N

Which member of each pair is less metallic? (a) I or O (b) Be or Ba (c) Se or Ge

State the type of bondingionic, covalent, or metallicyou would expect in each: (a) CsF(s); (b) N2(g); (c) Na(s).

State the type of bondingionic, covalent, or metallicyou would expect in each: (a) ICl3(g); (b) N2O(g); (c) LiCl(s).

State the type of bondingionic, covalent, or metallicyou would expect in each: (a) O3(g); (b) MgCl2(s); (c) BrO2(g).

State the type of bondingionic, covalent, or metallicyou would expect in each: (a) Cr(s); (b) H2S(g); (c) CaO(s).

Draw a Lewis electron-dot symbol for (a) Rb; (b) Si; (c) I.

Draw a Lewis electron-dot symbol for (a) Ba; (b) Kr; (c) Br.

Draw a Lewis electron-dot symbol for (a) Sr; (b) P; (c) S.

Draw a Lewis electron-dot symbol for (a) As; (b) Se; (c) Ga.

Give the group number and general electron configuration of an element with each electron-dot symbol: (a) X (b) X

Give the group number and general electron configuration of an element with each electron-dot symbol: (a) X (b) X

If energy is required to form monatomic ions from metals and nonmetals, why do ionic compounds exist?

(a) In general, how does the lattice energy of an ionic compound depend on the charges and sizes of the ions? (b) Ion arrangements of three general salts are represented below. Rank them in order of increasing lattice energy. 2+ 2 2+ 2+ 2 2+ 2 2+ 2+ 2+2 2+ 2 2+ 2 2 2+ 2 2 2+ 2 2 B C

When gaseous Na1 and Cl2 ions form gaseous NaCl ion pairs, 548 kJ/mol of energy is released. Why, then, does NaCl occur as a solid under ordinary conditions?

To form S22 ions from gaseous sulfur atoms requires 214 kJ/mol, but these ions exist in solids such as K2S. Explain.

Use condensed electron configurations and Lewis electron-dot symbols to depict the ions formed from each of the following atoms, and predict the formula of their compound: (a) Ba and Cl (b) Sr and O (c) Al and F (d) Rb and O

Use condensed electron configurations and Lewis electron-dot symbols to depict the ions formed from each of the following atoms, and predict the formula of their compound: (a) Cs and S (b) O and Ga (c) N and Mg (d) Br and Li

For each ionic compound formula, identify the main group to which X belongs: (a) XF2; (b) MgX; (c) X2SO4.

For each ionic compound formula, identify the main group to which X belongs: (a) X3PO4; (b) X2(SO4)3; (c) X(NO3)2.

For each ionic compound formula, identify the main group to which X belongs: (a) X2O3; (b) XCO3; (c) Na2X.

For each ionic compound formula, identify the main group to which X belongs: (a) CaX2; (b) Al2X3; (c) XPO4.

For each pair, choose the compound with the larger lattice energy, and explain your choice: (a) BaS or CsCl; (b) LiCl or CsCl.

For each pair, choose the compound with the larger lattice energy, and explain your choice: (a) CaO or CaS; (b) BaO or SrO.

For each pair, choose the compound with the smaller lattice energy, and explain your choice: (a) CaS or BaS; (b) NaF or MgO.

For each pair, choose the compound with the smaller lattice energy, and explain your choice: (a) NaF or NaCl; (b) K2O or K2S.

Use the following to calculate DH 8 lattice of NaCl: Na(s) Na(g) DH8 5 109 kJ Cl2(g) 2Cl(g) DH8 5 243 kJ Na(g) Na1(g) 1 e2 DH8 5 496 kJ Cl(g) 1 e2 Cl2(g) DH8 5 2349 kJ Na(s) 1 1 2Cl2(g) NaCl(s) DH8 5 2411 kJ Compared with the lattice energy of LiF (1050 kJ/mol), is the magnitude of the value for NaCl what you expected? Explain.

Use the following to calculate DH 8 lattice of MgF2: Mg(s) - Mg(g) DH 8 5 148 kJ F2(g) - 2F(g) DH 8 5 159 kJ Mg(g) - Mg1(g) 1 e2 DH 8 5 738 kJ Mg1(g) - Mg21(g) 1 e2 DH 8 5 1450 kJ F(g) 1 e2- F2(g) DH 8 5 2328 kJ Mg(s) 1 F2(g) - MgF2(s) DH 8 5 21123 kJ Compared with the lattice energy of LiF (1050 kJ/mol) or the lattice energy you calculated for NaCl in Problem 9.30, does the relative magnitude of the value for MgF2 surprise you? Explain.

Aluminum oxide (Al2O3) is a widely used industrial abrasive (emery, corundum), for which the specific application depends on the hardness of the crystal. What does this hardness imply about the magnitude of the lattice energy? Would you have predicted from the chemical formula that Al2O3 is hard? Explain.

Born-Haber cycles were used to obtain the first reliable values for electron affinity by considering the EA value as the unknown and using a theoretically calculated value for the lattice energy. Use a Born-Haber cycle for KF and the following values to calculate a value for the electron affinity of fluorine: K(s) K(g) DH 8 5 90 kJ K(g) K1(g) 1 e2 DH 8 5 419 kJ F2(g) 2F(g) DH 8 5 159 kJ K(s) 1 1 2F2(g) KF(s) DH 8 5 2569 kJ K1(g) 1 F2(g) KF(s) DH 8 5 2821 kJ

Describe the interactions that occur between individual chlorine atoms as they approach each other and form Cl2. What combination of forces gives rise to the energy holding the atoms together and to the final internuclear distance?

Define bond energy using the HCl bond as an example. When this bond breaks, is energy absorbed or released? Is the accompanying DH value positive or negative? How do the magnitude and sign of this DH value relate to the value that accompanies HCl bond formation?

For single bonds between similar types of atoms, how does the strength of the bond relate to the sizes of the atoms? Explain.

How does the energy of the bond between a given pair of atoms relate to the bond order? Why?

When liquid benzene (C6H6) boils, does the gas consist of molecules, ions, or separate atoms? Explain.

Using the periodic table only, arrange the members of each of the following sets in order of increasing bond strength: (a) BrBr, ClCl, II (b) SH, SBr, SCl (c) CN, CN, CN

Using the periodic table only, arrange the members of each of the following sets in order of increasing bond length: (a) HF, HI, HCl (b) CS, CO, CO (c) NH, NS, NO

Formic acid (HCOOH; structural formula shown below) is secreted by certain species of ants when they bite. H H C O O Rank the relative strengths of (a) the CO and CO bonds and (b) the HC and HO bonds. Explain these rankings.

Write a solution Plan (without actual numbers, but including the bond energies you would use and how you would combine them algebraically) for calculating the total enthalpy change of the following reaction: H2(g) 1 O2(g) - H2O2(g) (HiOiOiH)

The text points out that, for similar types of substances, one with weaker bonds is usually more reactive than one with stronger bonds. Why is this generally true?

Why is there a discrepancy between a heat of reaction obtained from calorimetry and one obtained from bond energies?

Which of the following gases would you expect to have the greater heat of reaction per mole for combustion? Why? H H C O H H H C H methane or formaldehyde

Which of the following gases would you expect to have the greater heat of reaction per mole for combustion? Why? H H C H H H C O H ethanol or methanol H C H O H

Use bond energies to calculate the heat of reaction: H H C C HH H H H H C C Cl Cl Cl Cl

Use bond energies to calculate the heat of reaction: O C O + 2 H H O O H N C N H H H N + H H H

An important industrial route to extremely pure acetic acid is the reaction of methanol with carbon monoxide: H H C H H C O H H O H H + C O O C Use bond energies to calculate the enthalpy of reaction.

Sports trainers treat sprains and soreness with ethyl bromide. It is manufactured by reacting ethylene with hydrogen bromide: H B C C r HH H H H H C C H Br H H + Use bond energies to find the enthalpy of reaction.

Describe the vertical and horizontal trends in electronegativity (EN) among the main-group elements. According to Paulings scale, what are the two most electronegative elements? The two least electronegative elements?

What is the general relationship between IE1 and EN for the elements? Why?

Is the HO bond in water nonpolar covalent, polar covalent, or ionic? Define each term, and explain your choice.

How does electronegativity differ from electron affinity?

How is the partial ionic character of a bond in a diatomic molecule related to DEN for the bonded atoms? Why?

Using the periodic table only, arrange the elements in each set in order of increasing EN: (a) S, O, Si; (b) Mg, P, As.

Using the periodic table only, arrange the elements in each set in order of increasing EN: (a) I, Br, N; (b) Ca, H, F.

Using the periodic table only, arrange the elements in each set in order of decreasing EN: (a) N, P, Si; (b) Ca, Ga, As.

Using the periodic table only, arrange the elements in each set in order of decreasing EN: (a) Br, Cl, P; (b) I, F, O.

Use Figure 9.21, p. 381, to indicate the polarity of each bond with a polar arrow: (a) NB; (b) NO; (c) CS; (d) SO; (e) NH; (f) ClO.

Use Figure 9.21, p. 381, to indicate the polarity of each bond with partial charges: (a) BrCl; (b) FCl; (c) HO; (d) SeH; (e) AsH; (f) SN.

Which is the more polar bond in each of the following pairs from Problem 9.60: (a) or (b); (c) or (d); (e) or (f)?

Which is the more polar bond in each of the following pairs from Problem 9.61: (a) or (b); (c) or (d); (e) or (f)?

Are the bonds in each of the following substances ionic, nonpolar covalent, or polar covalent? Arrange the substances with polar covalent bonds in order of increasing bond polarity: (a) S8 (b) RbCl (c) PF3 (d) SCl2 (e) F2 (f) SF2

Are the bonds in each of the following substances ionic, nonpolar covalent, or polar covalent? Arrange the substances with polar covalent bonds in order of increasing bond polarity: (a) KCl (b) P4 (c) BF3 (d) SO2 (e) Br2 (f) NO2

Rank the members of each set of compounds in order of increasing ionic character of their bonds. Use polar arrows to indicate the bond polarity of each: (a) HBr, HCl, HI (b) H2O, CH4, HF (c) SCl2, PCl3, SiCl4

Rank the members of each set of compounds in order of decreasing ionic character of their bonds. Use partial charges to indicate the bond polarity of each: (a) PCl3, PBr3, PF3 (b) BF3, NF3, CF4 (c) SeF4, TeF4, BrF3

The energy of the CC bond is 347 kJ/mol, and that of the ClCl bond is 243 kJ/mol. Which of the following values might you expect for the CCl bond energy? Explain. (a) 590 kJ/mol (sum of the values given) (b) 104 kJ/mol (difference of the values given) (c) 295 kJ/mol (average of the values given) (d) 339 kJ/mol (greater than the average of the values given)

(a) List four physical characteristics of a solid metal. (b) List two chemical characteristics of a metallic element.

Briefly account for the following relative values: (a) The melting points of Na and K are 898C and 638C, respectively. (b) The melting points of Li and Be are 1808C and 12878C, respectively. (c) Li boils more than 11008C higher than it melts.

Magnesium metal is easily deformed by an applied force, whereas magnesium fluoride is shattered. Why do these two solids behave so differently?

Geologists have a rule of thumb: when molten rock cools and solidifies, crystals of compounds with the smallest lattice energies appear at the bottom of the mass. Suggest a reason for this.

Acetylene gas (ethyne; HCPCH) burns in an oxyacetylene torch to produce carbon dioxide and water vapor. The heat of reaction for the combustion of acetylene is 1259 kJ/mol. (a) Calculate the CPC bond energy, and compare your value with that in Table 9.2, p. 371. (b) When 500.0 g of acetylene burns, how many kilojoules of heat are given off? (c) How many grams of CO2 form? (d) How many liters of O2 at 298 K and 18.0 atm are consumed?

Use Lewis electron-dot symbols to represent the formation of (a) BrF3 from bromine and fluorine atoms; (b) AlF3 from aluminum and fluorine atoms.

Even though so much energy is required to form a metal cation with a 21 charge, the alkaline earth metals form halides with general formula MX2, rather than MX. (a) Use the following data to calculate DH8 f of MgCl: Mg(s) Mg(g) DH8 5 148 kJ Cl2(g) 2Cl(g) DH8 5 243 kJ Mg(g) Mg1(g) 1 e2 DH8 5 738 kJ Cl(g) 1 e2 Cl2(g) DH8 5 2349 kJ DH8 lattice of MgCl 5 783.5 kJ/mol (b) Is MgCl favored energetically relative to Mg and Cl2? Explain. (c) Use Hesss law to calculate DH8 for the conversion of MgCl to MgCl2 and Mg (DH8 f of MgCl2 5 2641.6 kJ/mol). (d) Is MgCl favored energetically relative to MgCl2? Explain.

Gases react explosively if the heat released when the reaction begins is sufficient to cause more reaction, which leads to a rapid expansion of the gases. Use bond energies to calculate DH8 of each of the following reactions, and predict which occurs explosively: (a) H2(g) 1 Cl2(g) - 2HCl(g) (b) H2(g) 1 I2(g) - 2HI(g) (c) 2H2(g) 1 O2(g) - 2H2O(g)

By using photons of specific wavelengths, chemists can dissociate gaseous HI to produce H atoms with certain speeds. When HI dissociates, the H atoms move away rapidly, whereas the heavier I atoms move more slowly. (a) What is the longest wavelength (in nm) that can dissociate a molecule of HI? (b) If a photon of 254 nm is used, what is the excess energy (in J) over that needed for dissociation? (c) If this excess energy is carried away by the H atom as kinetic energy, what is its speed (in m/s)?

In developing the concept of electronegativity, Pauling used the term excess bond energy for the difference between the actual bond energy of XY and the average bond energies of XX and YY (see text discussion for the case of HF). Based on the values in Figure 9.21, p. 381, which of the following substances contains bonds with no excess bond energy? (a) PH3 (b) CS2 (c) BrCl (d) BH3 (e) Se8

Use condensed electron configurations to predict the relative hardnesses and melting points of rubidium (Z 5 37), vanadium (Z 5 23), and cadmium (Z 5 48).

Without stratospheric ozone (O3), harmful solar radiation would cause gene alterations. Ozone forms when the bond in O2 breaks and each O atom reacts with another O2 molecule. It is destroyed by reaction with Cl atoms formed when the CCl bond in synthetic chemicals breaks. Find the wavelengths of light that can break the CCl bond and the bond in O2.

Inert xenon actually forms many compounds, especially with highly electronegative fluorine. The DH8 f values for xenon difluoride, tetrafluoride, and hexafluoride are 2105, 2284, and 2402 kJ/mol, respectively. Find the average bond energy of the XeF bonds in each fluoride.

The HF bond length is 92 pm, 16% shorter than the sum of the covalent radii of H (37 pm) and F (72 pm). Suggest a reason for this difference. Similar data show that the difference becomes smaller down the group, from HF to HI. Explain.

There are two main types of covalent bond breakage. In homolytic breakage (as in Table 9.2, p. 371), each atom in the bond gets one of the shared electrons. In some cases, the electronegativity of adjacent atoms affects the bond energy. In heterolytic breakage, one atom gets both electrons and the other gets none; thus, a cation and an anion form. (a) Why is the CC bond in H3CCF3 (423 kJ/mol) stronger than that in H3CCH3 (376 kJ/mol)? (b) Use bond energy and any other data to calculate the enthalpy of reaction for the heterolytic cleavage of O2.

Find the longest wavelengths of light that can cleave the bonds in elemental nitrogen, oxygen, and fluorine.

The work function (f) of a metal is the minimum energy needed to remove an electron from its surface. (a) Is it easier to remove an electron from a gaseous silver atom or from the surface of solid silver (f 5 7.59310219 J; IE 5 731 kJ/mol)? (b) Explain the results in terms of the electron-sea model of metallic bonding.

Lattice energies can also be calculated for covalent solids using a Born-Haber cycle, and the network solid silicon dioxide has one of the highest DH8 lattice values. Silicon dioxide is found in pure crystalline form as transparent rock quartz. Much harder than glass, this material was once prized for making lenses for optical devices and expensive spectacles. Use Appendix B and the following data to calculate DH8lattice of SiO2: Si(g) Si(g) DH 8 5 454 kJ Si(g) Si41(g) 1 4e2 DH 8 5 9949 kJ O2(g) 2O(g) DH 8 5 498 kJ O(g) 1 2e2 O22(g) DH 8 5 737 kJ

The average CH bond energy in CH4 is 415 kJ/mol. Use Table 9.2 (p. 371) and the following to calculate the average CH bond energy in ethane (C2H6; CC bond), in ethene (C2H4; CC bond), and in ethyne (C2H2; CC bond): C2H6(g) 1 H2(g) 2CH4(g) DH8rxn 5 2265.07 kJ/mol C2H4(g) 1 2H2(g) 2CH4(g) DH8rxn 5 2202.21 kJ/mol C2H2(g) 1 3H2(g) 2CH4(g) DH8rxn 5 2376.74 kJ/mol

Carbon-carbon bonds form the backbone of nearly every organic and biological molecule. The average bond energy of the CC bond is 347 kJ/mol. Calculate the frequency and wavelength of the least energetic photon that can break an average CC bond. In what region of the electromagnetic spectrum is this radiation?

In a future hydrogen-fuel economy, the cheapest source of H2 will certainly be water. It takes 467 kJ to produce 1 mol of H atoms from water. What is the frequency, wavelength, and minimum energy of a photon that can free an H atom from water?

Dimethyl ether (CH3OCH3) and ethanol (CH3CH2OH) are constitutional isomers (see Table 3.4, p. 113). (a) Use Table 9.2 (p. 371) to calculate DH 8 rxn for the formation of each compound as a gas from methane and oxygen; water vapor also forms. (b) State which reaction is more exothermic. (c) Calculate DH 8 rxn for the conversion of ethanol to dimethyl ether.

Enthalpies of reaction calculated from bond energies and from enthalpies of formation are often, but not always, close to each other. (a) Industrial ethanol (CH3CH2OH) is produced by a catalytic reaction of ethylene (CH2CH2) with water at high pressures and temperatures. Calculate DH 8 rxn for this gas-phase hydration of ethylene to ethanol, using bond energies and then using enthalpies of formation. (b) Ethylene glycol is produced by the catalytic oxidation of ethylene to ethylene oxide, which then reacts with water to form ethylene glycol: O CH (l) 2 CH2 H HOCH2CH2OH(l) + 2O(l) The DH8 rxn for this hydrolysis step, based on enthalpies of formation, is 297 kJ/mol. Calculate DH8 rxn for the hydrolysis using bond energies. (c) Why are the two values relatively close for the hydration in part (a) but not close for the hydrolysis in part (b)?