NaGroup

1

ClGroup

7

Naming Compounds That Contain aMetal and a Nonmetal (Types I and II)

AIM: To learn to name binary compounds of a metal anda nonmetal.

As we saw in Section 4.11, when a metal such as sodium combines with anonmetal such as chlorine, the resulting compound contains ions. Themetal loses one or more electrons to become a cation, and the nonmetalgains one or more electrons to form an anion. The resulting substance iscalled a binary ionic compound. Binary ionic compounds contain a pos-itive ion (cation), which is always written first in the formula, and a nega-tive ion (anion). To name these compounds we simply name the ions.

In this section we will consider binary ionic compounds of two typesbased on the cations they contain. Certain metal atoms form only onecation. For example, the Na atom always forms Na�, never Na2� or Na3�.Likewise, Cs always forms Cs�, Ca always forms Ca2�, and Al always formsAl3�. We will call compounds that contain this type of metal atom Type Ibinary compounds and the cations they contain Type I cations. Examplesof Type I cations are Na�, Ca2�, Cs�, and Al3�.

124

5.2• • • • •

C H E M I S T R Y I N F O C U S

Sugar of Lead

In ancient Roman society it was common to boilwine in a lead-lined vessel, driving off much of thewater to produce a very sweet, viscous syrupcalled sapa. This syrup was commonly used as asweetener for many types of food and drink.

We now realize that a major component of thissyrup was lead acetate, Pb(C2H3O2)2. This com-pound has a very sweet taste—hence its originalname, sugar of lead.

Many historians believe that the fall of theRoman Empire was due at least in part to lead poi-soning, which causes lethargy and mental mal-functions. One major source of this lead was thesapa syrup. In addition, the Romans’ highlyadvanced plumbing system employed lead waterpipes, which allowed lead to be leached into theirdrinking water.

Sadly, this story is more relevant to today’ssociety than you might think. Lead-based solderwas widely used for many years to connect thecopper pipes in water systems in homes and com-mercial buildings. There is evidence that danger-ous amounts of lead can be leached from thesesoldered joints into drinking water. In fact, largequantities of lead have been found in the waterthat some drinking fountains and water coolersdispense. In response to these problems, the U.S.

Congress has passed a law banning lead from thesolder used in plumbing systems for drinkingwater.

An ancient painting showing Romans drinking wine.

370770_ch_05.qxd 1/14/03 8:31 AM Page 124 mac48 Mac 48: 420_kec: