6.2. Electron Configuration and the Periodic Table http://www.ck12.org
other noble gases soon followed. The group was originally called theinert gasesbecause they were believed to be
completely unreactive and unable form compounds. However, beginning in the early 1960s, several compounds of
xenon were synthesized by treating it with highly reactive fluorine gas. The name of the group was later changed to
noble gases.
The number of valence electrons in elements of thep-block is equal to the group number minus 10. As an example,
sulfur is located in Group 16, so it has 16 –10 = 6 valence electrons. Since sulfur is located in period 3, its outer
electron configuration is 3s^23 p^4. In the older system of labeling groups, the representative elements are designated
1A through 8A. Using this system, the number of valence electrons is equal to the number preceding the letter A.
Using the same example, sulfur is a member of Group 6A, so it has 6 valence electrons.
The properties of thep-block elements vary widely. The stair-step line separating metals from nonmetals runs
through thep-block. As a result, this block includes 8 metals, all 7 metalloids, and all nonmetals except for hydrogen.
Note that there is some variation among different periodic tables over how to classify the rare elements polonium and
astatine. The metals of thep-block are much more stable than thes-block metals. Aluminum and tin are frequently
used in packaging, and lead (Figure6.12) is used in car batteries, bullets, and radiation shields.
FIGURE 6.12
Lead blocks are used in radiation shield-
ing.The elements of Group 17 (fluorine, chlorine, bromine, iodine, and astatine) are called thehalogens. The halogens
all have the general electron configurationns^2 np^5 , giving them seven valence electrons. They are one electron short
of having full outersandpsublevels, which makes them very reactive. They undergo especially vigorous reactions
with the reactive alkali metals. In their pure elemental forms, chlorine and fluorine are gases at room temperature,
bromine is a dark orange liquid, and iodine is a dark purple-gray solid. Astatine is so rare that its properties are
mostly unknown.
Watch videos of experiments involving thep-block elements:
- Superconductors! at http://education.jlab.org/frost/superconductor.html
- The Flying Ring at http://education.jlab.org/frost/ring_fling.html
- Superconducting BAYCO Bits at http://education.jlab.org/scienceseries/superconducitng_bayco_bits.html
- Halogen Activity Series at http://www.dlt.ncssm.edu/core/Chapter8-Atomic_Str_Part2/bleachoverlay-lg.htm
- Reaction of Bromine with Aluminum at http://www.youtube.com/watch?v=zZAiYc3WVXM
- Halogen Displacement Reactions at http://www.youtube.com/watch?v=cbFCWFksYoM