The Foundations of Chemistry

Exercises 303

*62.Write acceptable Lewis formulas for the following com-

mon air pollutants: (a) SO 2 ; (b) NO 2 ; (c) CO; (d) O 3

(ozone); (e) SO 3 ; (f) (NH 4 ) 2 SO 4. Which one is a solid?

Which ones exhibit resonance? Which ones violate the

octet rule?

Formal Charges

*63.Assign a formal charge to each atom in the following:

(a) (d)

(b) O S O

O

O C O

2 

Cl

Cl O

*70.How does one predict that a covalent bond between two

atoms is polar?

*71.Ionic compounds generally have a higher melting point

than covalent compounds. What is the major difference in

the structures of ionic and covalent compounds that

explains the difference in melting points?

*72.Explain why the electrons in the carbon–fluorine cova-

lent bond tend to move more toward the halogen atom

than do the electrons in the carbon–bromine covalent

bond.

*73.Why do we show only partial charges, and not full charges,

on the atoms of a polar molecule?

*74.In each pair of bonds, indicate the more polar bond, and

use and to show the direction of polarity in each

bond.

(a) CXO and CXN

(b) BXO and PXS

(c) PXH and PXN

(d) BXH and BXI

*75.The molecule below is urea, a compound used in plastics

and fertilizers.

(a) Which bonds in this molecule are polar and which are

nonpolar?

(b) Which is the most polar bond in the molecule? Which

atom is the partial negative end of this bond?

*76.(a) Which two of the following pairs of elements are most

likely to form ionic bonds? Te and H; C and F; Ba and F;

N and F; K and O. (b) Of the remaining three pairs, which

one forms the least polar, and which the most polar, cova-

lent bond?

*77.(a) List three reasonably nonpolar covalent bonds between

dissimilar atoms. (b) List three pairs of elements whose

compounds should exhibit extreme ionic character.

*78.Classify the bonding between the following pairs of

atoms as ionic, polar covalent, or nonpolar covalent. (a) Li

and O; (b) Br and I; (c) Na and H; (d) O and O; (e) H

and O.

*79.For each of the following, tell whether the bonding is pri-

marily ionic or covalent.

(a) potassium and iodine in potassium iodide;

(b) beryllium and the nitrate ion in beryllium nitrate;

(c) the carbon–carbon bond in CH 3 CH 3 ;

(d) carbon and oxygen in carbon monoxide;

(e) phosphorus and oxygen in the phosphate ion.

*80.Identify the bond in each of the following bonded pairs

that is likely to have the greater proportion of “ionic char-

acter.”

(a) NaXCl or MgXCl; (b) CaXS or FeXS;

(c) AlXBr or OXBr; (d) RaXH or CXH.

N

H H

H H

C

O

N

(c) (e)

*64.Assign a formal charge to each atom in the following:

(a) (b) (c) O C O

F F

F

P

F F

F As F

F

O Cl O

O O

O O

Cl O O Cl O

O

O



(d) (e)

*65.With the aid of formal charges, explain which Lewis for-

mula is more likely to be correct for each given molecule.

(a) For Cl 2 O,

(b) For HN 3 ,

(c) For N 2 O,

*66.Write Lewis formulas for three different atomic arrange-

ments with the molecular formula HCNO. Indicate all

formal charges. Predict which arrangement is likely to be

the least stable and justify your selection.

Ionic Versus Covalent Character and Bond Polarities

*67.Distinguish between polar and nonpolar covalent bonds.

*68.Why is an HCl molecule polar but a Cl 2 molecule is non-

polar?

*69.How does one predict that the chemical bonding between

two elements is likely to be ionic?

NON or NNO

H NNN or H NNN

Cl O Cl or Cl Cl O

Cl Al Cl

Cl

Cl



O N O