How to find Electron configuration for elements and ions using Aufbau principle, Periodic table?
Home > How to write an electron configuration?
Electron configuration is the arrangement of electrons in atomic orbitals. It represents the electrons in numbers. Electron configuration is used to predict the properties of a group of elements. It helps in describing the electronic structure of an atom.
In this article, we will discuss the following things
 How to write Electron configuration using the Aufbau principle.
 How to find Electron configuration using Periodic table.
 How to write Electron configuration with a noble gas or in shorthand notation.
 How to do Electron configuration for ions(Positive and negatively charged atoms).
 How to draw Orbital diagrams using Electron configuration.
 The electron configuration of the first 30 elements, and exceptions as well.
How to write Electron configuration using Aufbau Principle?
To write the electron configuration of elements using the Aufbau principle, we have to first find the total number of electrons in a given element, then we have to fill the orbitals with electrons from lower energy to higher energy, i.e. the electrons will be filled into 1s orbital first then 2s, then 2p…so on.
Aufbau Principle:
 The word ‘Aufbau’ in German means ‘building up’.
 The Aufbau rule simply gives the order of electrons filling in the orbital of an atom in its ground state.
 It states that the orbital with the lowest energy level will be filled first before those with high energy levels. In short, the electrons will be filled in the orbital in order of their increasing energies.
 For example, the 1s orbital will be filled first with electrons before the 2s orbital.
Simply understand that there are commonly four different types of subshells – s, p, d, and, f.
These subshells can hold a maximum number of electrons on the basis of a formula, 2(2l + 1) where ‘l’ is the azimuthal quantum number.
Value of ‘l’ for different subshells.
Subshells  Value of ‘l’  Maximum number of electrons, 2(2l + 1)  Number of orbitals in the subshell 
s  0  2  1 
p  1  6  3 
d  2  10  5 
f  3  14  7 
So, in short, the s subshell can hold a maximum of 2 electrons(1 orbital), the p subshell can hold 6 electrons(3 orbitals), the d subshell can hold 10 electrons(5 orbitals), and the f subshell can hold at most 14 electrons(7 orbitals).
Now, the electron configuration of an atom can be built by filling the electrons in a lower energy subshell first then higher, higher, and higher.
Generally, (n + l) rule is used to predict the energy level of subshells.
n = principle quantum number
l = Azimuthal quantum number
⇒ Lower the value of (n + l) for an subshell, the lower its energy, hence, it will be filled first with electrons.
⇒ For two different subshells having same (n + l) value, then the subshell with lower value of n has lower energy.
So, all these are basics of How filling of electrons will be done in different subshells, obviously, you don’t have so much time for writing electron configuration by using so many rules.
Therefore, we have a diagonal rule for electron filling order in the different subshells using the Aufbau principle.
So, the order in which the orbitals are filled with electrons from lower energy to higher energy is – 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s < 5f < 6d < 7p and so on.
Note: S orbital can hold maximum of 2 electrons, P orbital can hold 6 electrons, D orbital can hold 10 electrons, and F orbital can hold maximum of 14 electrons.
Let’s take an example to understand How to write the electron configuration for elements using the Aufbau principle.
How to find the electron configuration of Carbon using the Aufbau Principle?
First of all, to determine the electron configuration for Carbon, we have to find the total number of electrons in it.
“The number of electrons in an atom is equal to the atomic number of an element, for neutrally charged species.”
 So, a Carbon atom is a neutral atom that has 6 atomic numbers which implies it has a total of 6 electrons.
 As per the Aufbau rule, the electrons will be filled into 1s orbital first then 2s, then 2p…so on.
 Now, for the electron configuration of Carbon, the first 2 electrons will go in 1s orbital since s subshell can hold a maximum of 2 electrons.
 The next two electrons will go in the 2s orbital, after that, we are left with 2 electrons, these will go in the 2p orbital since the p subshell can hold a maximum of 6 electrons.
 Therefore, the electron configuration of Carbon will be 1s^{2}2s^{2}2p^{2}.
How to find the electron configuration of Magnesium using the Aufbau Principle?
 A Magnesium atom is a neutral atom that has an atomic number of 12 which implies it has a total of 12 electrons.
 As per the Aufbau rule, the electrons will be filled into 1s orbital first then 2s, then 2p…so on.
 Now, for the electron configuration of Magnesium, the first 2 electrons will go in 1s orbital since s subshell can hold a maximum of 2 electrons.
 The next two electrons will go into the 2s orbital, after that, the next 6 electrons will go into the 2p orbital since the p subshell can hold up to 6 electrons.
 Now, we are left with 2 electrons, this will go in a 3s orbital.
 Therefore, the electron configuration of Magnesium will be 1s^{2}2s^{2}2p^{6}3s^{2}.
How to write the electron configuration of Potassium using the Aufbau Principle?
 A Potassium atom is a neutral atom that has an atomic number of 19 which implies it has a total of 19 electrons.
 As per the Aufbau rule, the electrons will be filled into 1s orbital first then 2s, then 2p…so on.
 Now, for the electron configuration of Potassium, the first 2 electrons will go in 1s orbital since s subshell can hold a maximum of 2 electrons.
 The next two electrons will go into the 2s orbital, after that, the next 6 electrons will go into the 2p orbital since the p subshell can hold up to 6 electrons.
 The next two electrons will go into the 3s orbital, and after that, the next six electrons will go into the 3p orbital, finally, the remaining one electron will go into the 4s orbital.
 Therefore, the electron configuration of Potassium will be 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{1}.
That’s all, It is the simplest method to write the electron configuration for a given element. For the first 30 elements in the periodic table, we must know How to find their electron configuration.
The electron configuration for the first 30 elements –
Atomic number  Name of the Elements  Electron configuration 
1  Hydrogen electron configuration  1s^{1} 
2  Helium electron configuration  1s^{2} 
3  Lithium electron configuration  1s^{2}2s^{1} 
4  Beryllium electron configuration  1s^{2}2s^{2} 
5  Boron electron configuration  1s^{2}2s^{2} 2p^{1} 
6  Carbon electron configuration  1s^{2}2s^{2} 2p^{2} 
7  Nitrogen electron configuration  1s^{2}2s^{2} 2p^{3} 
8  Oxygen electron configuration  1s^{2}2s^{2} 2p^{4} 
9  Fluorine electron configuration  1s^{2}2s^{2} 2p^{5} 
10  Neon electron configuration  1s^{2}2s^{2} 2p^{6} 
11  Sodium electron configuration  1s^{2}2s^{2} 2p^{6}3s^{1} 
12  Magnesium electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 
13  Aluminum electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{1} 
14  Silicon electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{2} 
15  Phosphorus electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{3} 
16  Sulfur electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{4} 
17  Chlorine electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{5} 
18  Argon electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{6} 
19  Potassium electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{6}4s^{1} 
20  Calcium electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{6}4s^{2} 
21  Scandium electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{6}3d^{1} 4s^{2} 
22  Titanium electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{6}3d^{2} 4s^{2} 
23  Vanadium electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{6}3d^{3} 4s^{2} 
24  Chromium electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{6}3d^{5} 4s^{1} 
25  Manganese electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{6}3d^{5} 4s^{2} 
26  Iron electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{6}3d^{6} 4s^{2} 
27  Cobalt electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{6}3d^{7} 4s^{2} 
28  Nickel electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{6}3d^{8} 4s^{2} 
29  Copper electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{6}3d^{10} 4s^{1} 
30  Zinc electron configuration  1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{6}3d^{10} 4s^{2} 
In the above list of the first 30 elements of electron configuration, there are two exceptions, the first is Chromium(Cr), and the second is Copper(Cu). They violate the Aufbau principle rule to get more stability.
The remaining 28 elements have electron configuration as proposed by the Aufbau principle rule.
Let’s understand it.
The actual electron configuration for Chromium is 1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{6}3d^{5} 4s^{1}, and not 1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{6}3d^{4} 4s^{2}(as proposed by the Aufbau principle).
Same as the actual electron configuration for Copper is 1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{6}3d^{10} 4s^{1}, and not 1s^{2}2s^{2} 2p^{6}3s^{2} 3p^{6}3d^{9} 4s^{2}(as proposed by the Aufbau principle).
“The reason for being this, they deviate from normal electronic configuration to get extra stability by halffilled and fulfilled configuration.”
“The completely filled dorbital offers more stability than the partially filled configuration.”
“There are two main exceptions to electron configuration: chromium and copper. In these cases, a completely full or half full d sublevel is more stable than a partially filled d sublevel, so an electron from the 4s orbital is excited and rises to a 3d orbital.”
How to use electron configuration to draw the orbital for any element
The main difference between the orbital diagram and electron configuration is that an orbital diagram shows electrons in form of arrows whereas an electron configuration shows electrons in form of numbers. Also, the orbital diagram shows details on the spin of electrons whereas the electron configuration doesn’t show it.
Both these follow the Aufbau principle (Diagonal rule).
There are three rules followed for drawing the orbital diagram for an atom.
(1). Aufbau’s principle: This rule state that the lower energy orbital will be filled before the higher energy orbital, for example – the 1s orbital will fill before the 2s orbital.
(2). Hund’s rule: This rule state that each orbital of a given subshell should be filled with one electron each before pairing them. That means “Each orbital gets one electron first, before adding the second electron to the orbital”.
(3). Pauli Exclusion Principle: This rule state that, no two electrons can occupy the same orbital with the same spin. That means “One must be spin up (↑) and one must be spin down (↓)”.
If you understand the above rules then constructing the orbital diagram or orbital notation for any element is super easy.
Basics of Orbital diagram and electron configuration:
There are different types of orbitals – s, p, d, and, f. These orbitals contain a number of boxes that can hold a number of electrons. Let’s see.
Each box will hold a maximum of 2 electrons with opposite spin.
 S orbital contains 1 box that can hold a maximum of 2 electrons.
 P orbital contains 3 boxes that can hold a maximum of 6 electrons.
 D orbital contains 5 boxes that can hold a maximum of 10 electrons.
 F orbital contains 7 boxes that can hold a maximum of 14 electrons.
The orbital diagram will also be filled with the same order as described by the Aufbau principle. (1s < 2s < 2p < 3s……and so on.)
Let’s take some examples to understand this
How to draw the orbital diagram for Oxygen using its electron configuration?
We know the electron configuration of Oxygen is 1s^{2}2s^{2}2p^{4}, now for drawing its orbital diagram, we need to show its electrons in form of an arrow in different boxes using Hund’s and Pauli exclusion rule.
 The orbital diagram of Oxygen contains 1s orbital, 2s orbital, and 2p orbital. 1s orbital contains 1 box, 2s orbital also contains 1 box and 2p orbital contains 3 boxes.
 Oxygen has a total of 8 electrons and one box can hold up to the two electrons.
 Therefore, the first two electrons will go in the 1s orbital, and the next two will go in the 2s orbital, now we are left with 4 electrons.
 These 4 electrons will go in the 2p orbital, since, the 2p orbital has 3 boxes, so, these electrons will be filled using Hund’s rule. (Each box gets one electron first, then start pairing).
How to draw the orbital diagram for Calcium using its electron configuration?
We know the electron configuration of Calcium is 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}, now for drawing its orbital diagram, we need to show its electrons in form of an arrow in different boxes using Hund’s and Pauli’s exclusion rule.
 The orbital diagram of Calcium contains 1s orbital, 2s orbital, 2p orbital, 3s orbital, 3p orbital, and 4s orbital. 1s orbital contains 1 box, 2s orbital also contains 1 box, 2p orbital contains 3 boxes, 3s orbital contains 1 box, 3p orbital contains 3 boxes, and 4s orbital contains 1 box.
 Calcium has a total of 20 electrons and one box can hold up to two electrons.
 Therefore, the first two electrons will go into the 1s orbital, the next two will go into the 2s orbital, and after that, the next six electrons will go into the 2p orbital, since, the 2p orbital has 3 boxes.
 After that, the next two electrons will go into the 3s orbital, and the next six electrons will enter the 3p orbital. Now, the 3p orbital is full.
 Therefore, the remaining two electrons will go in the 4s orbital.
How to write the electron configuration for the ions (positive and negative charges)?
The process of finding the electron configurations for ions, cation(positive charge) and, anion(negative charge) is very similar to neutral atoms, in the case of cation, we have to remove the electrons, and in the case of anion, we have to add the electrons to the configuration of atoms.
First of all, understand what are ions.
“Ion, any atom or group of atoms that bears one or more positive or negative electrical charges. Positively charged ions are called cations; negatively charged ions, anions.”
⇒ When an atom loses electrons it becomes a positive ion (called a cation).
⇒ When an atom gains electrons it becomes a negative ion (called anion).
Let’s understand with an example.
How to write the electron configuration for the Na^{+} ion?
 We know, in general, that the electron configuration of Sodium (Na) is 1s^{2}2s^{2}2p^{6}3s^{1}.
 Now, in the Na^{+} ion, the positive charge means, Sodium loses one electron.
 Therefore, to write the electron configuration of the Na^{+} ion, we have to remove one electron from the configuration of Sodium (Na).
 The resulting electron configuration for the Sodium ion (Na^{+}) will be 1s^{2}2s^{2}2p^{6}. It resembles the configuration of the nearest inert gas i.e Neon.
How to write the electron configuration for the O^{2} ion?
 We know, in general, that the electron configuration of Oxygen (O) is 1s^{2}2s^{2}2p^{4}.
 Now, in O^{2} ion, the negative charge means, oxygen has gained two extra electrons.
 Therefore, to write the electron configuration of O^{2} ion, we have to add two electrons to the configuration of Oxygen (O).
 The resulting electron configuration for Oxide ion (O^{2}) will be 1s^{2}2s^{2}2p^{6}. It resembles the configuration of the nearest inert gas i.e Neon.
How to write the electron configuration for the Al^{3+} ion?
 We know, in general, that the electron configuration of Aluminum (Al) is 1s^{2}2s^{2}2p^{6}3s^{2}3p^{1}.
 Now, in the Al^{3+} ion, the positive charge means, Aluminum loses three electrons.
 Therefore, to write the electron configuration of the Al^{3+} ion, we have to remove three electrons from the configuration of Aluminum (Al).
 The resulting electron configuration for the Al^{3+} will be 1s^{2}2s^{2}2p^{6}. It resembles the configuration of the nearest inert gas i.e Neon.
Let’s check the list of some important ions with their electron configuration.
Ions  Gain or loss of electrons  Electron configuration 
Li^{+}  Lithium loses one electron  1s^{2}2s^{1} → 1s^{2} 
Be^{2+}  Beryllium loses two electrons  1s^{2}2s^{2} → 1s^{2} 
B^{3+}  Boron loses three electrons  1s^{2}2s^{2}2p^{1} → 1s^{2} 
C^{4}  Carbon has gained four extra electrons  1s^{2}2s^{2} 2p^{2 }→ 1s^{2}2s^{2}2p^{6} 
N^{3}  Nitrogen has gained three extra electrons  1s^{2}2s^{2} 2p^{3 }→ 1s^{2}2s^{2}2p^{6} 
O^{2}  oxygen has gained two extra electrons  1s^{2}2s^{2} 2p^{4 }→ 1s^{2}2s^{2}2p^{6} 
F^{}  Fluorine has gained one extra electron  1s^{2}2s^{2} 2p^{5 }→ 1s^{2}2s^{2}2p^{6} 
Na^{+}  Sodium loses one electron  1s^{2}2s^{2}2p^{6}3s^{1} → 1s^{2}2s^{2}2p^{6} 
Mg^{2+}  Magnesium loses two electrons  1s^{2}2s^{2}2p^{6}3s^{2} → 1s^{2}2s^{2}2p^{6} 
Al^{3+}  Aluminum loses three electrons  1s^{2}2s^{2}2p^{6}3s^{2}3p^{1 }→ 1s^{2}2s^{2}2p^{6} 
Si^{4+}  Silicon loses four electrons  1s^{2}2s^{2}2p^{6}3s^{2}3p^{2 }→ 1s^{2}2s^{2}2p^{6} 
P^{3}  Phosphorus gains three electrons  1s^{2}2s^{2}2p^{6}3s^{2}3p^{3 }→ 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6} 
S^{2}  Sulfur gains two electrons  1s^{2}2s^{2}2p^{6}3s^{2}3p^{4 }→ 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6} 
Cl^{}  Chlorine gains one electron  1s^{2}2s^{2}2p^{6}3s^{2}3p^{5 }→ 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6} 
K^{+}  Potassium loses one electron  1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{1 }→ 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6} 
Ca^{2+}  Calcium loses two electrons  1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2 }→ 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6} 
How to find electron configuration using the periodic table?
The electron configuration of elements can also be found by using the periodic table.
 Start with the Hydrogen atom in the periodic table
 “Glide Across Each Row, Left to Right and Top to Bottom, Writing Out the Electron Configuration Until you get to your element”
 S orbital can hold a maximum of 2 electrons, P orbital can hold 6 electrons, and D orbital can hold a maximum of 10 electrons.
Image credit → Electron configuration
For example – Write the Electron configuration of Aluminum using only the Periodic table.
 Start with the hydrogen atom, and glide across, left to right. We get, 1s + 1s = 1s^{²}.
 Head over to the next row, where, we get, 2s^{2} and 2p^{6}.
 Again move to the next row, and write – 3s^{2} and 3p^{1}.
 So, the final electron configuration for Aluminum is 1s^{2}2s^{2}2p^{6}3s^{2}3p^{1}.
You can confirm this electron configuration whether is right or not, by adding the superscripts number and then matching it with the total number of electrons in the element, if they are the same, then the electron configuration is correct.
⇒ Aluminum has total number of 13 electrons, and by adding the above electron configuration superscript numbers, we get, 2 + 2 + 6 + 2 + 1 = 13 electrons, hence, the above electron configuration of Aluminum is totally correct.
I am advising you to watch the video given below to understand, How to write the electron configuration of elements using only a Periodic table.
How to write electron configuration in shorthand notation or with noble gas?
The shorthand notation of electron configurations is also called the noble gas configuration.
To write the noble gas configuration or shorthand electron configurations, we have to start with the symbol of the noble gas in the previous period, followed by the configuration of the remaining electrons for a given element.
“A noble gas or shorthand configuration of an atom consists of the elemental symbol of the last noble gas prior to that atom, followed by the configuration of the remaining electrons”
Important Noble gases are –
⇒ Helium (He) → atomic number 2
⇒ Neon (Ne) → atomic number 10
⇒ Argon (Ar) → atomic number 18
Let’s take some examples to understand How to find noble gas electron configuration for given elements.
How to write the noble gas configuration for Oxygen (O)?
 We know, the full electron configuration for oxygen is 1s^{2}2s^{2}2p^{4}. The noble gas before the oxygen atom is Helium (He) which has a 1s^{2} electron configuration.
 So, to write the electron configuration for oxygen in noble gas form or in shorthand notation, we have to replace the portion of the oxygen electron configuration with the symbol of Helium noble gas, [He].
 The noble gas or shorthand electron configuration for oxygen is [He] 2s^{2}2p^{4}.
How to write the noble gas configuration for Sodium (Na)?
 We know, the full electron configuration for sodium is 1s^{2}2s^{2}2p^{6}3s^{1}. The noble gas before the sodium atom is Neon (Ne) which has a 1s^{2}2s^{2}2p^{6} electron configuration.
 So, to write the electron configuration for sodium in noble gas form or in shorthand notation, we have to replace the portion of the sodium electron configuration with the symbol of Neon noble gas, [Ne].
 The noble gas or shorthand electron configuration for Sodium is [Ne] 3s^{1}.
How to write the noble gas configuration for Calcium (Ca)?
 We know, the full electron configuration for calcium is 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}. The noble gas before the calcium atom is Argon (Ar) which has a 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6} electron configuration.
 So, to write the electron configuration for calcium in noble gas form or in shorthand notation, we have to replace the portion of the calcium electron configuration with the symbol of Argon noble gas, [Ar].
 The noble gas or shorthand electron configuration for Calcium is [Ar] 4s^{2}.
Atomic number  Name of the Elements  Shorthand or Noble gas configuration 
1  Hydrogen (H)  1s^{1} 
2  Helium (He)  1s^{2} 
3  Lithium (Li)  [He] 2s^{1} 
4  Beryllium (Be)  [He] 2s^{2} 
5  Boron (B)  [He] 2s^{2} 2p^{1} 
6  Carbon (C)  [He] 2s^{2} 2p^{2} 
7  Nitrogen (N)  [He] 2s^{2} 2p^{3} 
8  Oxygen (O)  [He] 2s^{2} 2p^{4} 
9  Fluorine (F)  [He] 2s^{2} 2p^{5} 
10  Neon (Ne)  [He] 2s^{2} 2p^{6} 
11  Sodium (Na)  [Ne] 3s^{1} 
12  Magnesium (Mg)  [Ne] 3s^{2} 
13  Aluminium (Al)  [Ne] 3s^{2} 3p^{1} 
14  Silicon (Si)  [Ne] 3s^{2} 3p^{2} 
15  Phosphorus (P)  [Ne] 3s^{2} 3p^{3} 
16  Sulphur (S)  [Ne] 3s^{2} 3p^{4} 
17  Chlorine (Cl)  [Ne] 3s^{2} 3p^{5} 
18  Argon (Ar)  [Ne] 3s^{2} 3p^{6} 
19  Potassium (K)  [Ar] 4s^{1} 
20  Calcium (Ca)  [Ar] 4s^{2} 
21  Scandium (Sc)  [Ar] 3d^{1} 4s^{2} 
22  Titanium (Ti)  [Ar] 3d^{2} 4s^{2} 
23  Vanadium (V)  [Ar] 3d^{3} 4s^{2} 
24  Chromium (Cr)  [Ar] 3d^{5} 4s^{1} 
25  Manganese (Mn)  [Ar] 3d^{5} 4s^{2} 
26  Iron (Fe)  [Ar] 3d^{6} 4s^{2} 
27  Cobalt (Co)  [Ar] 3d^{7} 4s^{2} 
28  Nickel (Ni)  [Ar] 3d^{8} 4s^{2} 
29  Copper (Cu)  [Ar] 3d^{10} 4s^{1} 
30  Zinc (Zn)  [Ar] 3d^{10} 4s^{2} 
How to find electron configuration using the Bohr model (Orbit)?
Bohr model describes the visual representation of orbiting electrons around the small nucleus. It used different electron shells such as K, L, M, N…so on.
These electron shells hold a specific number of electrons that can be calculated via the 2n^{2} formula where n represents the shell number.
Electron shells  Shell number (n)  Max. number of electrons (2n^{2}) 
K  1  2 
L  2  8 
M  3  18 
N  4  32 
So, K is the first shell or orbit that can hold up to 2 electrons, L is the 2nd shell which can hold up to 8 electrons, M is the third shell that can hold up to 18 electrons, and N is the fourth shell that can hold up to 32 electrons.
Let’s find the Electron configuration of Sulfur through the Bohr model.
Now, Sulfur has an atomic number of 16 and it contains a total number of 16 electrons. Hence, 2 electrons will go in the first shell(K), 8 electrons will go in the second shell(L), and the remaining six electrons will go in the third shell(M).
Therefore, the electrons per shell for Sulfur are 2, 8, 6, hence, we can say, based on the shell, the electronic configuration of the Sulfur atom is [2, 8, 6].
Let’s check out the Electronic configuration of the first 30 elements based on their shell.
Name of element  Number of electrons  Electronic configuration based on shell 
Hydrogen (H)  1  1 
Helium (He)  2  2 
Lithium (Li)  3  [2, 1] 
Beryllium (Be)  4  [2, 2] 
Boron (B)  5  [2, 3] 
Carbon (C)  6  [2, 4] 
Nitrogen (N)  7  [2, 5] 
Oxygen (O)  8  [2, 6] 
Fluorine (F)  9  [2, 7] 
Neon (Ne)  10  [2, 8] 
Sodium (Na)  11  [2, 8, 1] 
Magnesium (Mg)  12  [2, 8, 2] 
Aluminum (Al)  13  [2, 8, 3] 
Silicon (Si)  14  [2, 8, 4] 
Phosphorus (P)  15  [2, 8, 5] 
Sulfur (S)  16  [2, 8, 6] 
Chlorine (Cl)  17  [2, 8, 7] 
Argon (Ar)  18  [2, 8, 8] 
Potassium (K)  19  [2, 8, 8, 1] 
Calcium (Ca)  20  [2, 8, 8, 2] 
Let’s checkout – How to draw Bohr model for any atom
FAQ
What is Ground state electron configuration, How to find it? 
The ground state configuration of an atom is the same as its regular electron configuration in which electrons remain in the lowest possible energy. The groundstate electron configuration is calculated in the same way, as deduced from the Aufbau principle. For example – ⇒ The ground state configuration of the sodium atom is 1s^{2}2s^{2}2p^{6}3s^{1}. ⇒ The ground state configuration of the magnesium atom is 1s^{2}2s^{2}2p^{6}3s^{2}. ⇒ The ground state configuration of the nitrogen atom is 1s^{2}2s^{2}2p^{3}. 
What are the rules needed to write the Electron configuration of an element? 
There are three rules that must be followed while writing the electronic configuration of elements. The rules are – the Aufbau principle, Pauli’s exclusion principle, and Hund’s rule. 
How to write the electron configuration for Noble gases? 
The electron configuration for noble gases is

What are the different types of Notation used to depict the Electron configuration? 
There are mainly three notations used to depict the Electron configuration. The three notations are – Orbital notation, SPDF notation, and Noble gas notations. 
What are the main exceptions in writing the Electron configuration? 
There are two main exceptions in Electron configuration – Chromium, and Copper. Let’s explain it. ⇒ Chromium has 24 electrons, so, according to Aufbau principle, it electrons configuration should be – 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{4}4s^{2}. But it is incorrect. The actual electron configuration for Chromium is – 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{5}4s^{1}.
⇒ Copper has 29 electrons, so, according to Aufbau principle, it electrons configuration should be – 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{9}4s^{2}. But it is incorrect. The actual electron configuration for Copper is – 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{1}.

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