How to find Electron configuration for elements and ions using Aufbau principle, Periodic table?

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 1s²2s²2p².

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 1s²2s²2p⁶3s².

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 1s²2s²2p⁶3s²3p⁶4s¹.

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	1s1
2	Helium electron configuration	1s2
3	Lithium electron configuration	1s22s1
4	Beryllium electron configuration	1s22s2
5	Boron electron configuration	1s22s22p1
6	Carbon electron configuration	1s22s22p2
7	Nitrogen electron configuration	1s22s22p3
8	Oxygen electron configuration	1s22s22p4
9	Fluorine electron configuration	1s22s22p5
10	Neon electron configuration	1s22s22p6
11	Sodium electron configuration	1s22s22p63s1
12	Magnesium electron configuration	1s22s22p63s2
13	Aluminum electron configuration	1s22s22p63s23p1
14	Silicon electron configuration	1s22s22p63s23p2
15	Phosphorus electron configuration	1s22s22p63s23p3
16	Sulfur electron configuration	1s22s22p63s23p4
17	Chlorine electron configuration	1s22s22p63s23p5
18	Argon electron configuration	1s22s22p63s23p6
19	Potassium electron configuration	1s22s22p63s23p64s1
20	Calcium electron configuration	1s22s22p63s23p64s2
21	Scandium electron configuration	1s22s22p63s23p63d14s2
22	Titanium electron configuration	1s22s22p63s23p63d24s2
23	Vanadium electron configuration	1s22s22p63s23p63d34s2
24	Chromium electron configuration	1s22s22p63s23p63d54s1
25	Manganese electron configuration	1s22s22p63s23p63d54s2
26	Iron electron configuration	1s22s2 2p63s23p63d64s2
27	Cobalt electron configuration	1s22s22p63s23p63d74s2
28	Nickel electron configuration	1s22s22p63s23p63d84s2
29	Copper electron configuration	1s22s22p63s23p63d104s1
30	Zinc electron configuration	1s22s22p63s23p63d104s2

Also check:

• Electron configuration for all 118 elements in the Periodic table

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 1s²2s² 2p⁶3s² 3p⁶3d⁵ 4s¹, and not 1s²2s² 2p⁶3s² 3p⁶3d⁴ 4s²(as proposed by the Aufbau principle).

Same as the actual electron configuration for Copper is 1s²2s² 2p⁶3s² 3p⁶3d¹⁰ 4s¹, and not 1s²2s² 2p⁶3s² 3p⁶3d⁹ 4s²(as proposed by the Aufbau principle).

“The reason for being this, they deviate from normal electronic configuration to get extra stability by half-filled and fulfilled configuration.”

“The completely filled d-orbital 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 sub-level is more stable than a partially filled d sub-level, so an electron from the 4s orbital is excited and rises to a 3d orbital.”

Also see – Electron configuration in excited states.

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 spins.

• 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 in 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 1s²2s²2p⁴, 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 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 two electrons.
• Therefore, the first two electrons will go into the 1s orbital, and the next two will go into 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 1s²2s²2p⁶3s²3p⁶4s², 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.

Check – Electron configuration calculator to count the electron configuration for any atom

How to write the electron configuration for the ions (positive and negative charges)?

The process of finding the electron configurations for ions, cations (positive charge) and, anions (negative charge) is very similar to neutral atoms, in the case of a cation, we have to remove the electrons, and in the case of an 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.”

Also check-

• Ion electron configuration calculator

⇒ 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 1s²2s²2p⁶3s¹.
• 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 1s²2s²2p⁶. 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 1s²2s²2p⁴.
• Now, in O^2- ion, the negative charge means, oxygen has gained two extra electrons.
• Therefore, to write the electron configuration of the O^2- ion, we have to add two electrons to the configuration of Oxygen (O).
• The resulting electron configuration for the Oxide ion (O^2-) will be 1s²2s²2p⁶. It resembles the configuration of the nearest inert gas i.e Neon.

How to write the electron configuration for the Al³⁺ ion?

• We know, in general, that the electron configuration of Aluminum (Al) is 1s²2s²2p⁶3s²3p¹.
• Now, in the Al³⁺ ion, the positive charge means, Aluminum loses three electrons.
• Therefore, to write the electron configuration of the Al³⁺ ion, we have to remove three electrons from the configuration of Aluminum (Al).
• The resulting electron configuration for the Al³⁺ will be 1s²2s²2p⁶. 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	1s22s1 → 1s2
Be2+	Beryllium loses two electrons	1s22s2 → 1s2
B3+	Boron loses three electrons	1s22s22p1 → 1s2
C4-	Carbon has gained four extra electrons	1s22s2 2p2 → 1s22s22p6
N3-	Nitrogen has gained three extra electrons	1s22s2 2p3 → 1s22s22p6
O2-	oxygen has gained two extra electrons	1s22s2 2p4 → 1s22s22p6
F–	Fluorine has gained one extra electron	1s22s2 2p5 → 1s22s22p6
Na+	Sodium loses one electron	1s22s22p63s1 → 1s22s22p6
Mg2+	Magnesium loses two electrons	1s22s22p63s2 → 1s22s22p6
Al3+	Aluminum loses three electrons	1s22s22p63s23p1 → 1s22s22p6
Si4+	Silicon loses four electrons	1s22s22p63s23p2 → 1s22s22p6
P3-	Phosphorus gains three electrons	1s22s22p63s23p3 → 1s22s22p63s23p6
S2-	Sulfur gains two electrons	1s22s22p63s23p4 → 1s22s22p63s23p6
Cl–	Chlorine gains one electron	1s22s22p63s23p5 → 1s22s22p63s23p6
K+	Potassium loses one electron	1s22s22p63s23p64s1 → 1s22s22p63s23p6
Ca2+	Calcium loses two electrons	1s22s22p63s23p64s2 → 1s22s22p63s23p6

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, 2s² and 2p⁶.
• Again move to the next row, and write – 3s² and 3p¹.
• So, the final electron configuration for Aluminum is 1s²2s²2p⁶3s²3p¹.

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 a 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”

Also check – Abbreviated or noble gas electron configuration calculator

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 configurations for given elements.

How to write the noble gas configuration for Oxygen (O)?

• We know, the full electron configuration for oxygen is 1s²2s²2p⁴. The noble gas before the oxygen atom is Helium (He) which has a 1s² 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] 2s²2p⁴.

How to write the noble gas configuration for Sodium (Na)?

• We know, the full electron configuration for sodium is 1s²2s²2p⁶3s¹. The noble gas before the sodium atom is Neon (Ne) which has a 1s²2s²2p⁶ 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] 3s¹.

How to write the noble gas configuration for Calcium (Ca)?

• We know, the full electron configuration for calcium is 1s²2s²2p⁶3s²3p⁶4s². The noble gas before the calcium atom is Argon (Ar) which has a 1s²2s²2p⁶3s²3p⁶ 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] 4s².

Atomic number	Name of the Elements	Shorthand or Noble gas configuration
1	Hydrogen (H)	1s1
2	Helium (He)	1s2
3	Lithium (Li)	[He] 2s1
4	Beryllium (Be)	[He] 2s2
5	Boron (B)	[He] 2s2 2p1
6	Carbon (C)	[He] 2s2 2p2
7	Nitrogen (N)	[He] 2s2 2p3
8	Oxygen (O)	[He] 2s2 2p4
9	Fluorine (F)	[He] 2s2 2p5
10	Neon (Ne)	[He] 2s2 2p6
11	Sodium (Na)	[Ne] 3s1
12	Magnesium (Mg)	[Ne] 3s2
13	Aluminium (Al)	[Ne] 3s2 3p1
14	Silicon (Si)	[Ne] 3s2 3p2
15	Phosphorus (P)	[Ne] 3s2 3p3
16	Sulfur (S)	[Ne] 3s2 3p4
17	Chlorine (Cl)	[Ne] 3s2 3p5
18	Argon (Ar)	[Ne] 3s2 3p6
19	Potassium (K)	[Ar] 4s1
20	Calcium (Ca)	[Ar] 4s2
21	Scandium (Sc)	[Ar] 3d1 4s2
22	Titanium (Ti)	[Ar] 3d2 4s2
23	Vanadium (V)	[Ar] 3d3 4s2
24	Chromium (Cr)	[Ar] 3d5 4s1
25	Manganese (Mn)	[Ar] 3d5 4s2
26	Iron (Fe)	[Ar] 3d6 4s2
27	Cobalt (Co)	[Ar] 3d7 4s2
28	Nickel (Ni)	[Ar] 3d8 4s2
29	Copper (Cu)	[Ar] 3d10 4s1
30	Zinc (Zn)	[Ar] 3d10 4s2

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 2n² formula where n represents the shell number.

Electron shells	Shell number (n)	Max. number of electrons (2n2)
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 into the first shell(K), 8 electrons will go into the second shell(L), and the remaining six electrons will go into 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?
• How to find valence electrons?

FAQ

How to find electron configuration?

“To calculate an electron configuration, divide the periodic table into sections to represent the atomic orbitals, the regions where electrons are contained. Groups one and two are the s-block, three through 12 represent the d-block, 13 to 18 are the p-block and the two rows at the bottom are the f-block.”

What is the easiest way to write electronic configuration?

The easiest way to write the electronic configuration for any element is by using a diagonal rule for electron filling order in the different subshells according to the Aufbau principle.

How do you write an electron configuration quickly?

By using the diagonal rule of the Aufbau principle, we can write electron configuration quickly. All we have to do is to remember the order in which the orbital is filled with electrons from lower energy to higher energy. The order of writing electron configuration is – 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s < 5f < 6d < 7p and so on.

What are the 3 rules for writing electron configurations?

The 3 rules for writing the electron configuration in the orbital box diagram are – the Aufbau rule, the Pauli-exclusion rule, and Hund’s Rule.

What is the electron configuration 1s2 2s2 2p6?

The electron configuration 1s2 2s2 2p6 represents the Neon (Ne) atom that has 10 electrons.

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 ground-state 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 1s22s22p63s1. ⇒ The ground state configuration of the magnesium atom is 1s22s22p63s2. ⇒ The ground state configuration of the nitrogen atom is 1s22s22p3.

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?

Noble gases commonly called Group 18, the inert gases, the rare gases, the helium family, or the neon family. The group consists of 6 elements: helium, neon, argon, krypton, xenon, and radon. The electron configuration for noble gases is- Helium (He) – 1s2 Neon (Ne) – 1s22s22p6 Argon (Ar) – 1s22s22p63s23p6 Krypton (Kr) – 1s22s22p63s23p63d104s24p6 Xenon (Xe) – 1s22s22p63s23p63d104s24p64d105s25p6 Radon (Rn) – 1s22s22p63s23p63d104s24p64d105s25p64f145d106s26p6

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 – 1s22s22p63s23p63d44s2. But it is incorrect. The actual electron configuration for Chromium is – 1s22s22p63s23p63d54s1. The reason for being this – Half-filled and fully filled subshell have extra stability, Therefore, one of the 4s orbital electrons jumps to the 3d orbital, so that it is half-filled. ⇒ Copper has 29 electrons, so, according to the Aufbau principle, its electron configuration should be – 1s22s22p63s23p63d94s2. But it is incorrect. The actual electron configuration for Copper is – 1s22s22p63s23p63d104s1. The reason is same, as we explained above, the fully filled subshell have extra stability, therefore, one of the 4s orbital electrons jumps to the 3d orbital, so that it is full-filled. Remember these exceptions in electron configuration – d4 and d9.