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282 CHEMISTRY FOR THE UTTERLY CONFUSED
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Don’t Forget!
Our goal in this chapter is to familiarize you with some properties of the elements,
as well as the periodic trends that you can observe in these properties.
You might want to review briefly the periodic trends we discussed in Chapter 8.
We will also discuss coordination compounds and complex ions. Again—
Practice, Practice, Practice.
There are exceptions to every “rule.” Hydrogen is nearly always an exception.
19-1 Hydrogen
Hydrogen is the only nonmetal in Group IA (1) on the periodic table. Some
periodic tables move hydrogen to other places, or list it in more than one place.
Hydrogen is capable of forming compounds with all elements except the noble
gases. In compounds with nonmetals, hydrogen usually behaves like a metal
instead of a nonmetal. Therefore, when hydrogen combines with a nonmetal, it
usually has a 1 oxidation number. When hydrogen combines with a metal, it
usually has a 1 oxidation number. Hydrogen compounds with the transition
metals are usually nonstoichiometric. Nonstoichiometric compounds have no
definite formula.
All Brønsted-Lowry and Arrhenius acids contain hydrogen. The formation or
transfer of hydrogen ions is the key to the behavior of all acids. You may wish
to review the behavior of acids in Chapters 4 and 15.
The standard cell potential for the reduction of hydrogen ions to hydrogen
gas is, by definition, 0.00 V. This potential is for the standard hydrogen electrode,
SHE, which is the reference to which we compare all other cell potentials.
All metals above hydrogen on the Activity Series will displace hydrogen
gas from acids. (See Chapter 4) Metals below hydrogen will not displace
hydrogen gas.