5.3 Representative Groups
Reading Focus
Key Concepts
Why do the elements in a group have similar properties?- What are some properties of the A groups in the periodic table?
Vocabulary
valence electron
alkali metals
alkaline earth metals
halogens
noble gases
Reading Strategy
Monitoring Your Understanding Copy the table below. As you read, record an important fact about each element listed.
Element |
Important Fact |
|---|---|
Magnesium |
a. |
Aluminum |
b. |
Chlorine |
c. |
WWhy is hydrogen located on the left side of the periodic table with the active metals? It is a nonmetal gas that seems to have more in common with the nonmetals in Group 17. Hydrogen's location is related to its electron configuration, not its properties.
Valence Electrons
Did you wonder why there are two numbering schemes on the periodic table in Figure 7? When the A groups are numbered from 1 through 8, they provide a useful reminder about the electron configurations of the elements in those groups. The number of an A group matches the number of valence electrons in an electron configuration for an element in that group. A valence electron is an electron that is in the highest occupied energy level of an atom. These electrons play a key role in chemical reactions. Properties vary across a period because the number of valence electrons increases from left to right.
Elements in a group have similar properties because they have the same number of valence electrons. These properties will not be identical because the valence electrons are in different energy levels. Valence electrons explain the location of hydrogen. Because hydrogen has a single valence electron, it is grouped with other elements, such as lithium, that have only one valence electron.
Figure 14 Because hydrogen is flammable, it can be used as a fuel in automobiles like this one. An engine that burns hydrogen has a key advantage over an engine that burns gasoline. Only water is produced when hydrogen burns.
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