The Foundations of Chemistry

II

n this chapter we examine some types of chemical reactions. Millions of reactions are

known, so it is useful to group them into classes, or types, so that we can deal system-

atically with these massive amounts of information. We will describe how some

compounds behave in aqueous solution, including how well their solutions conduct elec-

tricity and whether or not the compounds dissolve in water. We introduce several ways

to represent chemical reactions in aqueous solution—formula unit equations, total ionic

equations, and net ionic equations—and the advantages and disadvantages of these methods.

Let us first take a brief look at the periodic table, which helps us to organize many

properties of the elements, including their chemical reactions.

THE PERIODIC TABLE: METALS, NONMETALS, AND

METALLOIDS

In 1869, the Russian chemist Dmitri Mendeleev (1834–1907) and the German chemist

Lothar Meyer (1830–1895) independently published arrangements of known elements

that are much like the periodic table in use today. Mendeleev’s classification was based

primarily on chemical properties of the elements, whereas Meyer’s classification was based

largely on physical properties. The tabulations were surprisingly similar. Both emphasized

the periodicity,or regular periodic repetition, of properties with increasing atomic weight.

Mendeleev arranged the known elements in order of increasing atomic weight in succes-

sive sequences so that elements with similar chemical properties fell in the same column.

He noted that both physical and chemical properties of the elements vary in a periodic

fashion with atomic weight. His periodic table of 1872 contained the 62 known elements

(Figure 4-1). Mendeleev placed H, Li, Na, and K in his table as “Gruppe I.” These were

4-1

Pronounced “men-del-lay-ev.”

Three of the halogens, elements

from Group VIIA (left to right):

chlorine, bromine, iodine.

Silicon (top), germanium (middle),

and tin (bottom), three elements from

Group IVA.