Orbital based electron configuration : The orbital-based electron configuration indicates exactly wherein an electron cloud an atom has the highest probability of receiving electrons.

In Article “Atom and Electron configuration 1”, we saw an electron configuration based on orbitals (Fe-26).

### [ **Orbital based electron configuration** ]

Why are s, p, and d so random in electron configuration? To describe it, we need to understand the “Aufbau policy.” Before that, let us know the values of electron orbit according to s, p, d, and f orbital.

As can be seen, the number of orbitals is twice the electron holding capacity. And which orbits or which orbitals there are, can also be seen here.

Now let us get back to the Aufbau policy.

The figure above illustrates the Afbau policy. Aufbau is a German word meaning building up.

The key to the Aufbau principle is that electrons will first enter a low-energy orbital. Then the electrons will go to the next strong orbital. Thus, the electrons will gradually become full in the orbitals.

Now in this figure, the orbitals applied to the orbital (n) values are written side by side. An arrow turns and crosses the orbitals. In the sequence or series of intersections, exactly in this series, the electrons will enter the orbitals.

This zigzag arrow image of the Aufbau principle of electron configuration basically indicates the sequential sequence of energy of the orbitals from small to large. Now the question is how is it diagnosed?

Orbital values **S = zero, p = 1, d = 2, f = 3** are used to determine the order of energy in this energy level. How these values came about will be described in the next article, Electron Format and Quantum Numbers.

Now let’s go back to the values. The power value of 1s will be 1; How?

**The order of energy is taken as the total energy level (n) + sub-energy level (l).**

So what is the value of 3d? The values of n = 3, d is 2, adding these two values is 3 + 2 = 5

So the power value of 3d is 5. Now if we determine the power value of 4s, we can see that 4 + 0 = 4, here the value of the power for 4s is less than 3d because the value of s is 0. Then the electron will first enter 4s and then enter 3d.

So let’s determine the values of 5d and 6p. There is a funny thing here.

d = 2 and p = 1, so the value of 5d is 5 + 2 = 7, the value of 6p is 6 + 1 = 7

Both values are 7, now where will the electron enter first? If the value is the same, the electron will enter the lower orbital sub-orbital first, that is, where the value of n is lower, the electron will enter first. Therefore, after entering the electron in 5d, the electron will enter in 6p.

The series of electron penetration is now understood. This principle is called the n + l rule. In this rule, the sub-energy level will be in order :

**1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p…**

Now in this order, two electrons will continue to enter in s, 6 in p, 10 in d, and 14 in f, as long as the atom has electrons.

Now the starting electron configuration of this article can be easily understood. The electron number of Fe is 26.

26 electrons will continue to enter the orbitals according to the Aufbau rules.

**26Fe => 1s2 2s2 2p6 3s2 3p6 4s2 3d6**

Now we understand the reason for the first electron entry in 4s. Although 3d has the capacity to hold 10 electrons, the electron configuration is complete after the entry of 6 electrons, since the number of electrons counted from the beginning completes 26.

By arranging according to the orbit, the electron configuration of Fe can be written as follows:

**26Fe => 1s2 2s2 2p6 3s2 3p6 3d6 4s2**

That is, the name of the element must be written at the beginning, then the electrons and orbitals have to be written by marking the arrow as instructed in the figure below.

So let us look at the electrons of a few elements in this way?

Sodium, **Na (11)** => 1s2 2s2 2p6 3s1

Magnesium, **Mg (12)** => 1s2 2s2 2p6 3s2

**K (19)** => 1s2 2s2 2p6 3s2 3p6 4s1

**Ca (20)** => 1s2 2s2 2p6 3s2 3p6 4s2

**Br (35)** => 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5

**Kr (36)** => 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6

**Pu (94)** => 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f6

Now, when an electron emits from the last energy level of Na, it becomes a Na+ ion. Then what will be its electron configuration?

Then 10 electrons of Na will exist.

Therefore,

**Na: 1s22s22p63s1 and Na+: 1s22s22p6.**

In the same way,

**P: 1s22s22p63s23p3 but, P3−: 1s22s22p63s23p6.**

For the electron configuration of an element, you need to know the number of electrons and the atomic number of the elements. Therefore, it is very important to know the periodic table. The chemistryGOLN.com article on the periodic table will be helpful in this regard.

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