Our next step is to write symbols for the outer electrons. In this case, the noble gas is argon, Ar, element 18.
We first locate Se in the table and then move backward from it through the table, from element 34 to 33 to 32 and so forth, until we come to the noble gas that precedes Se. Let's use the periodic table to write the electron configuration of selenium (Se, element 34). Using these facts, you can write the electron configuration of an element based merely on its position in the periodic table. Recall also that l s is the first s subshell, 2 p is the first p subshell, 3 d is the first d subshell, and 4 f is the first f subshell, as Figure 6.30 shows. Thus, the s block has 2 columns, the p block has 6, the d block has 10, and the f block has 14. Recall that 2, 6, 10, and 14 are the numbers of electrons that can fill the s, p, d, and f subshells, respectively. The number of columns in each block corresponds to the maximum number of electrons that can occupy each kind of subshell. In most tables, the f block is positioned below the periodic table to save space: Consequently, these elements are often referred to as the f-block metals. The elements in the two tan rows containing 14 columns are the ones in which the valence f orbitals are being filled and make up the f block. The order in which electrons are added to orbitals is read left to right beginning in the top left corner. Electron Configurations of Group 2A and 3A ElementsįIGURE 6.30 Regions of the periodic table.These are the elements in which the valence d orbitals are being filled and make up the d block. The orange block in Figure 6.30 has ten columns containing the transition metals. The s block and the p block elements together are the representative elements, sometimes called the main-group elements.
On the right is a block of six pink columns that comprises the p block, where the valence p orbitals are being filled. These two columns make up the s block of the periodic table. These elements, known as the alkali metals (group 1A) and alkaline earth metals (group 2A), are those in which the valence s orbitals are being filled. On the left are two blue columns of elements.
As TABLE 6.4 shows, for example, all 2A elements have an ns 2 outer configuration, and all 3A elements have an ns 2 np outer configuration, with the value of n increasing as we move down each column.Īs shown in FIGURE 6.30, the periodic table can be divided into four blocks based on the filling order of orbitals. Thus, elements in the same column of the table have related outer-shell (valence) electron configurations. We just saw that the electron configurations of the elements correspond to their locations in the periodic table. CHEMISTRY THE CENTRAL SCIENCE 6 ELECTRONIC STRUCTURE OF ATOMS 6.9 ELECTRON CONFIGURATIONS AND THE PERIODIC TABLE