Which sublevel is the first to be filled in an atom

Electron configurations can be written directly from the periodic table, without having to memorize the aufbau scheme, using the following patterns:. Half-filled and filled subshells are especially stable, leading to some anomalous electron configurations:. In the case of chromium, an electron from the 4 s orbital moves into a 3 d orbital, allowing each of the five 3 d orbitals to have one electron, making a half-filled set of orbitals.

In the case of copper, silver and gold, an electron from the highest-occupied s orbital moves into the d orbitals, thus filling the d subshell. Many anomalous electron configurations occur in the heavier transition metals and inner transition metals, where the energy differences between the s , d , and f subshells is very small.

Key: s-block p-block d-block f-block. Probably the least reliable method is to memorize the following list even though it shows the order of filling of all the orbitals necessary for describing the ground state electron configurations of all of the known elements. Instead of relying on memorization, you can use the memory aid shown below to remind you of the correct order of filling of the sublevels. The following steps explain how to write it and use it yourself.

Write the possible sublevels for each energy level in organized rows and columns like the image below. To do this, you need to remember that there is one sublevel on the first principal energy level, two on the second, three on the third, etc.

Every principal energy level has an s orbital. The second principal energy and all higher energy levels have a p sublevel. The d sublevels start on the third principal energy level, the f sublevels start on the fourth principal energy level, etc. Starting with the top arrow, follow the arrows one by one in the direction they point, listing the sublevels as you pass through them.

The sublevels that are not needed for describing the known elements are enclosed in parentheses below. We can also use the block organization of the periodic table, as shown below , to remind us of the order in which sublevels are filled. To do this, we move through the elements in the order of increasing atomic number, listing new sublevels as we come to them. Instead it shows the last sublevels filled in describing the electron configurations of the elements in each section.

We will use Figure 5. The arrows show the order in which the sublevels fill. In period 1, there are two boxes.

In the usual table, these boxes would contain the symbols for hydrogen and helium, the elements in this period. In Figure 5. In period 2, there are eight boxes. Instead of symbols for eight elements, Figure 5. Period 3 also has eight boxes, which would correspond to the electrons needed to fill the 3s and 3p sublevels. Look back now to Figure 5. Notice that the 4s sublevel is filled immediately after the 3p sublevel.

Figure 5. So we must start here a new period, period 4, and put boxes for the elements formed by filling the 4s sublevel in those columns. These are the first d electrons added, so we start new columns for the elements formed by their addition.

Ten electrons are needed to fill the five d orbitals, so we start ten columns in this fourth period, placing the columns next to column 2 and between it and column 3. The 4p sublevel is filled next, after the 3d sublevel.

The boxes for the elements formed by filling the p orbitals are in place under the boxes for elements formed by adding the 3p electrons. By consulting Figure 5. Boxes for the elements formed by filling the orbitals of these sublevels are arranged as were those in period 4. Just as period 4 contains more elements than period 3, period 6 contains more elements than period 5.

Period 6 starts with elements whose last added electron is in the 6s sublevel. The next step is where period 6 differs from period 5. Look again at Figure 5. We will need 14 boxes to contain the electrons needed to fill the seven f orbitals. These are the boxes of the lanthanide series, shown below the table.

There is some evidence that these orbitals do not fill before one electron is in a 5d orbital, so we have shown in Figure 5. After the 4f orbitals are filled, boxes are shown for the rest of the elements formed by adding 5d and 6p electrons. The seventh period contains boxes for the elements formed by filling the 7s, the 5f the actinide series shown below the table , and finally the 6d sublevels.

This relationship is further expressed by the following names sometimes given to parts of the table: columns 1 and 2 s block columns p block short columns d block lanthanides and actinides f block The groups of elements found in these blocks are also known by other names.