http://www.ck12.org Chapter 6. The Periodic Table
FIGURE 6.11
The alkaline earth metals include beryl-
lium, magnesium, calcium, strontium, and
barium. Strontium and barium react with
air and must be stored in oil.- Reaction of Sodium with Oxygen at http://www.youtube.com/watch?v=hxrQrOlWGH0
- Reaction of Potassium with Water at http://www.youtube.com/watch?v=oqMN3y8k9So
- Reaction of Potassium with Oxygen at http://www.youtube.com/watch?v=pT0w6BRfDGs
- Reaction of Magnesium with Oxygen at http://www.youtube.com/watch?v=NnFzHt6l4z8
- Reaction of Calcium with Water at http://www.youtube.com/watch?v=i-rFsFwdkTU
Hydrogen and Helium
Looking at the block diagram (Figure6.9), you may be wondering why hydrogen and helium were not included
in our discussion of the alkali metal and alkaline earth metal groups. Though hydrogen, with its 1s^1 configuration,
appears as though it should be similar to the rest of Group 1, it does not share the properties of that group. Hydrogen
is a unique element that cannot be reasonably included in any single group of the periodic table. Some periodic
tables even separate hydrogen’s square from the rest of Group 1 to indicate its solitary status.
Helium has a configuration of 1s^2 , which would seem to place it with the alkaline earth metals. However, it is instead
placed in Group 18 at the far right of the periodic table. The elements in this group, called the noble gases, are very
unreactive because their outermostsandpsublevels are completely filled. Since it is part of the first period, helium
does not have apsublevel. Its filled 1ssublevel makes it very similar to the other members of Group 18.
The
Thep-block consists of the elements in groups 13-18. Thepsublevel always fills after thessublevel of a given
principal energy level. Therefore, the general electron configuration for an element in thep-block isns^2 np^1 −^6. For
example, the electron configuration of elements in Group 13 isns^2 np^1 , the configuration of elements in Group 15 is
ns^2 np^3 , and so on.The elements of Group 18 (helium, neon, argon, krypton, xenon, and radon) are called thenoble
gases. They are an especially important group of the periodic table because they are almost completely unreactive,
due to their completely filled outermostsandpsublevels. As noted above, helium might at first seem to be out of
place because it has a configuration of 1s^2 instead of thens^2 np^6 configuration that is characteristic of the other noble
gases. However, because there are no 1porbitals, helium also has a completely filled outermost energy level, which
leads to the various chemical properties exhibited by the other noble gases. Note that the noble gases were not a part
of Mendeleev’s periodic table because they had not yet been discovered. In 1894, English physicist Lord Rayleigh
and Scottish chemist Sir William Ramsay detected argon as a small percentage of the atmosphere. Discovery of the