http://www.ck12.org Chapter 6. The Periodic Table
of the periodic table is related to electron configurations, which in turn influences chemical reactivity. We will first
start with the following introductory video: http://www.youtube.com/watch?v=5MMWpeJ5dn4 (3:51).
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Click image to the left for more content.Periods and Blocks
There are seven horizontal rows, or periods, on the periodic table. The length of each period is determined by
electron capacity of the sublevels that fill during that period, as seen inTable6.2.
TABLE6.2: Period Length and Sublevels in the Periodic Table
Period Number of Elements in Period Sublevels in Order of Filling
1 2 1s
2 8 2s 2p
3 8 3s 3p
4 18 4s 3d 4p
5 18 5s 4d 5p
6 32 6s 4f 5d 6p
7 32 7s 5f 6d 7pRecall that the four different sublevels (s, p, d, and f) each consist of a different number of orbitals. The s sublevel
has one orbital, the p sublevel has three orbitals, the d sublevel has five orbitals, and the f sublevel has seven orbitals.
In the first period, only the 1s sublevel is being filled. Since all orbitals can hold two electrons, the entire first period
consists of just two elements. In the second period, the 2s sublevel, with two electrons, and the 2p sublevel, with
six electrons, are being filled. Consequently, the second period contains eight elements. The third period is similar
to the second, except the 3s and 3p sublevels are being filled. Because the 3d sublevel does not fill until after the 4s
sublevel, the fourth period contains 18 elements, due to the 10 additional electrons that can be accommodated by the
3d orbitals. The fifth period is similar to the fourth. After the 6s sublevel fills, the 4f sublevel is populated with up
to 14 electrons. This is followed by the 5d and the 6p sublevels. The total number of elements in the sixth period is
- The seventh period also contains 32 elements, most of which are too unstable to be found in nature. All 32 have
been detected or synthesized, although for some of the later elements in this period, only a handful of atoms have
ever been made.
The period to which a given element belongs can easily be determined from its electron configuration. As an
example, consider the element nickel (Ni). Its electron configuration is [Ar]3d^8 4s^2. The highest occupied principal
energy level is the fourth, as indicated by the 4 in the 4s^2 portion of the configuration. Therefore, nickel can be found
in the fourth period of the periodic table.Figure6.3 shows a version of the periodic table that includes abbreviated
electron configurations.
Based on electron configurations, the periodic table can be divided into blocks denoting which sublevel is in the
process of being filled. The s, p, d, and f blocks are illustrated inFigure6.4.
Figure6.4 also illustrates how the d sublevel is always one principal level behind the period in which that sublevel