# Electron Configuration Calculator

## What is electron configuration and how to calculate with steps

Electron configuration means the distribution of electrons in the atomic orbitals of an atom. Electrons have various energy levels or shells around their nucleus of an atom.

These energy levels are further divided into sublevels, and each sublevel contains a certain number of orbitals. Each orbital can hold a maximum of two electrons with opposite spins according to the **Pauli exclusion principle**.

**To calculate electron configuration** you need to know some concepts such as What are **Shells**, **Subshells**, and **Orbitals** and some principles like **aufbau's prinicple** **hunds rule**

below you will learn each topic related to electronic configuration and how to calculate it with **steps**

## How to use Electron Configuration Calculator?

**1.** Select any element from the dropdown above or search within the dropdown by the name of the element or by using its atomic number. For example, you can search for "argon" by typing its name or for its atomic number "18".

**2.** Click on calculate button to check electronic configuration of that element and other details.

**3.** After clicking calculate button you will see electron configuration of that element. It will show other details too related to that element like atomic number, atomic mass , valence electrons.

## What are Shells, Subshells, and Orbitals?

According to Bohr's atomic model, there are fixed paths around the nucleus where electrons revolve. He called these paths as shells or energy levels.

These are energy levels are represented by small *n*.

For example, for first shell, we write *n = 1*. for second shell, we write *n = 2*. for the third shell, we write *n = 3*. for the fourth shell, we write *n = 4*.

Also remember that first shell is known as K shell, second shell is known as L shell, third shell is known as M shell, and fourth shell is known as N shell.

To sum up this whole concept,

we can write as, when *n = 1*, it is first shell or K shell. when *n = 2*, it is second shell or L shell. when *n = 3*, it is third shell or M shell. when *n = 4*, it is fourth shell or N shell.

Now, every shell is divided into subshells are sub-energy levels.

These are denoted by S, P, D and F , so K, L, M and N are main shells, while S,P,D,F are sub-shells within main shells.

The first or K shell has only one sub-shell S, the second or L shell has two sub-shells S and P, the third or M shell has three sub-shells S, P and D while the fourth or N shell has four sub-shells SPDF.

The most easy trick to remember the sub-shells is, first shell has only one sub-shell, second shell has two sub-shells, third shell has three sub-shells and fourth shell has four sub-shells.

Secondly, when you go from the first shell to the fourth shell, add one sub-shell successively.

Like S, then SP, then SPD and then SPDF.

Now ,

Look at below image,

If *n = 1* and we know that it is K shell and K shell has only one sub-shell which is s, and there is 1 with this s, because this s sub-shell belongs to first or K shell.

secondly *n = 2*, we know that it is L shell and there are two sub-shells which are s and p, there is 2 with this s and with this p, because this s and p belong to second shell.

thirdly *n = 3*, it is M shell and we know that there are three sub-shells s, p and d, there is 3 with s, p and d, because they belong to third shell.

fourthly *n = 4*, it is *n* shell and we know that it has four sub-shells, s, p, d and f, there is 4 with s, p, d and f, because they all belong to fourth shell.

let take a example, 3s and 4s, here can you guess the difference between them?

Well, 3 means third shell and s means sub-shell, so 3s means s is the sub-shell of the third shell, our M shell.

similarly 4s means s is the sub-shell of fourth shell our N shell

let me teach you that what are orbitals?

Well, the regions of sub-shells where probability of finding electrons is maximum are called orbitals.

you can say that these are the three dimensional paths where chances of finding electrons are maximum, for example s sub-shell has 1 orbital, p sub-shell has 3 orbitals and d sub-shell has 5 orbitals.

final words :

shells around the nucleus like when *n = 1*, it is K shell and it has 1 sub-shell 1s, when *n = 2* it is L shell and it has 2 sub-shells, 2s and 2p, when *n = 3* it is M shell and it has 3 sub-shells, 3s, 3p and 3d, when *n = 4* it is N shell and it has 4 sub-shells, 4s, 4p, 4d and 4f, this was all about shells, sub-shells and orbitals.

## Aufbau's principle

So let's take an example of sodium. Sodium has 11 electrons, and we want to configure the 11 electrons of sodium in 1s, 2s, 2p, and 3s orbitals. But here is the most important question. How should electrons of sodium be arranged in these orbitals?

I mean, firstly, should I place electrons in either 1s or 2s or 3s.

Well, to solve this problem, we use the aufbau principle.

Now, what is the aufbau principle? Well, the aufbau principle states that electrons fill orbitals of the lowest energy levels before occupying higher energy levels.

Remember that the aufbau principle is not the name of any scientist. It is a German word which means 'to build'.

Here, in the case of sodium, firstly, an electron will fill the 1s orbital. Secondly, an electron will fill the 2s orbital. Thirdly, an electron will fill the 2p orbital. And finally, an electron will fill the 3s orbital.

It is because the energy of 1s is smaller than 2s and so on.

So, we've noted down that the aufbau principle teaches us about filling orbitals in increasing order of energy. Also, you must learn how to find the energy of any orbital.

Well, the energy of orbitals is directly proportional to *N* plus *L*. Now, what is *N* and *L*?

*N* is the principle quantum number and *L* is the azimuthal quantum number.

For example,

We know that when *N* is equal to 1, it is the K shell. When *N* is equal to 2, it is the L shell. When *N* is equal to 3, it is the M shell. And when *N* is equal to 4, it is the N shell. Thus, remember that *N* starts from 1 and goes up to 4.

Similarly, we know that there are 4 sub-orbitals: S, P, D, and F. And for S, *L* is equal to 0. For P, *L* is equal to 1. For D, *L* is equal to 2. And for F, *L* is equal to 3. Thus, *L* starts from 0 and goes up to 3.

Now, consider 3s and 4p. Which orbital has more energy? 3s or 4p?

Well, in the case of 3s, *N* is equal to 3. For S, *L* is equal to 0.

So *N* plus *L* is equal to 3 plus 0. And we get 3.

And in the case of 4p, *N* is equal to 4. For P, *L* is equal to 1. So *N* plus *L* is equal to 4 plus 1. And we get 5.

Thus, 4p has more energy than 3s.

Because the *N* plus *L* value of 4p is greater than 3s. Therefore, according to the aufbau principle, electrons will firstly fill the 3s orbital due to having lower energy.

Also, you should know the special case.

For example, 3p and 4s. In the case of 3p, *N* is equal to 3.

For 4s, *N* is equal to 4. So *N* plus *L* is equal to 4.

And in the case of 4s, *N* is equal to 4. For S, *L* is equal to 0. So *N* plus *L* is equal to 4.

The value of *N* plus *L* is the same for both 3p and 4s. Do they have the same energy?

Well, the answer is no. They do not.

In such cases, when you get the same value of *N* plus *L* for 2 orbitals,

always decide based on the principle quantum number *N*.

The quantum number of 3p is *N* is equal to 3. And the quantum number of 4s is *N* is equal to 4.

So 3p has a lower principle quantum number than 4s.

Hence 3p has smaller energy and 4s has more energy.

Therefore, according to the aufbau principle, firstly, an electron will fill the 3p orbital and then the 4s orbital.

Finally, let me teach you the very common and easy trick of understanding the energy of orbitals. Now write some orbitals like 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 5s, 5p, and 6s.

Now, electrons will go into the 1s, then to 2s, then to 2p and 3s, then to 3p and 4s, then to 3d, 4p and 4s, then to 4d, 5p and 6s.

So the order of increasing energy of orbitals is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, and so on.

Thus, by this way, we can also find the energy of orbitals. According to the aufbau principle, we can then start placing electrons in these orbitals from the lower energy level.

## Calculate electron configuration using hund's rule

Now you know aufbau's principle and now we can write electron configuration of any element using aufbau's principle and hund's rule.

Let's take example of oxygen :

We know that its atomic number is 8.

I want to configure the 8 electrons of oxygen in 1s, 2s and 2p subshells. According to aufbau's principle, which we learned above, the energy of 1s is smaller than 2s and that of 2s is smaller than 2p.

Firstly, 2 electrons will fill the 1s, then 2 electrons will fill the 2s, and lastly, 4 electrons will fill the 2p subshell.

Now 2 plus 2 plus 4 is equal to 8.

So I have successfully configured the 8 electrons of oxygen in its subshells.

Also, we know that 1s has 1 orbital, 2s has also 1 orbital, and 2p has 3 orbitals.

Now here is the important question. How these 2 electrons should be placed in 1s and 2s orbitals, and how these 4 electrons should be placed in 3 orbitals of 2p? Well, this problem is solved by Hund's rule.

It states 2 important points.

**1.** it states that every orbital and a subshell is singly filled with 1 electron before any orbital is doubly filled. **2.** it states that all electrons in singly filled orbitals have the same spin.

Now we can easily fill the orbitals of oxygen using Hund's rule. So the 2 electrons of 1s can fill the orbital as 1 electron in upward direction. Does the second electron should be placed in 2s orbital? The answer is no.

Because the energy of 2s is higher than 1s, and 1s can easily accommodate 2 electrons. The second electron must be placed in 1s orbital, but in opposite direction. Here, 1s is completely filled.

Now, Electrons will start filling the orbital of 2s. 2s can accommodate 2 electrons. So one electron should be placed in upward direction, and second electron should be placed in downward direction.

Now here is the interesting part, How can we place these 4 electrons in the 3 orbitals of 2p?

Well, we will use the Hund's rule here.

As per hunds rule :

**1.** it states that every orbital and a subshell is singly filled before any orbital is doubly filled. It means that only one electron should be placed in each orbital of 2p. So I place 1-1 electron in each orbital of 2p in one direction.

**2.** it states that all electrons in singly filled orbitals have the same spin. So I have to correct the spin of this second electron. Now all these 3 orbitals are singly filled, and all electrons have the same spin.

What about the 4th electron? Well, Hund's rule states that once all orbitals are singly filled, you should then start placing second electron in them but in opposite direction. So I place the 4th electron in opposite direction in this orbital. This I have successfully filled the orbitals of oxygen and final configuration of oxygen is **1s2 2s2 2p4** by the help of Hund's rule.

## What are valence electrons?

the electrons found in the outermost shell, or valence shell of atom are known as Valence electrons. These electrons are responsible for chemical bonding and it determines reactivity and ability of an atom to form chemical bonds with other atoms.

The number of valence electrons an atom has corresponds to its position in the periodic table.

### Easiest trick to find valence electrons

**Step 1 :** first step is to find your element in periodic table and block of your element and its group number. You can find all in above periodic table.

In the periodic table picture above you can see there are 4 blocks of elements
- In red colour we have **S block** elements

- In yellow colour we have **P block** elements

- In blue colour we have **D block** elements

- In green colour we have **F block** elements

**S Block :** suppose you want to find valence electrons of an element from S block.

For example : **K (Potassium)** it is in S block and have group no. 1

for S block elements no of valence electrons is equal to its group no. so valence electrons in K (Potassium) is 1

**P Block :** suppose you want to find valence electrons of an element from P block.

For example : **C (carbon)** it is in P block and have group no. 14

for P block elements no of valence electrons is equal to its ( group no. - 10 ) so valence electrons in C (carbon) is 14 - 10 = 4

**For D Block :** Remember that all elements in D block have 2 valence electrons except Cr (Chromium) and Cu (Copper), these two has 1 valence electron