Short Answer

Electronic configuration is the arrangement of electrons in different shells, subshells, and orbitals around the nucleus of an atom. Since electrons occupy specific energy levels, their distribution follows certain rules such as the Aufbau principle, Pauli Exclusion Principle, and Hund’s Rule.

Electronic configuration helps us understand the chemical behaviour of elements. It explains why some elements are reactive, why some are inert, and why elements form certain types of bonds. It also determines the position of elements in the periodic table.

Detailed Explanation :

Electronic Configuration

Electronic configuration describes how electrons are arranged within an atom. Every atom contains electrons that occupy various energy levels or shells. These electrons are not placed randomly; instead, they follow an orderly pattern based on quantum mechanical principles. Electronic configuration provides a clear picture of this arrangement and helps predict the chemical and physical properties of an element.

Electrons occupy shells (K, L, M, N or n = 1, 2, 3, 4…) and subshells (s, p, d, f). Each subshell contains a certain number of orbitals, and each orbital can hold a maximum of two electrons. The way electrons fill these subshells determines the electronic configuration of an element.

Meaning of Electronic Configuration

Electronic configuration is defined as:

“The distribution of electrons in various shells, subshells, and orbitals of an atom.”

This arrangement follows a fixed sequence because electrons always fill the lowest energy level first and then move to higher ones.

The general order of filling subshells is:
1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → …

This sequence continues as atomic number increases.

Why Electronic Configuration is Important

Electronic configuration is an essential concept because it helps explain:

• Chemical reactivity of elements
• Valency and bonding behaviour
• Metallic and non-metallic nature
• Placement of elements in the periodic table
• Shape and type of molecules
• Properties like ion formation, oxidation state, and stability

The outermost electrons, called valence electrons, play a key role in determining how an atom will react with others.

Shells and Subshells in Electronic Configuration

1. Shells

Shells are energy levels represented by:

• K (n = 1)
• L (n = 2)
• M (n = 3)
• N (n = 4)

Each shell has a maximum capacity given by the formula 2n².

For example:

• K-shell: 2 electrons
• L-shell: 8 electrons
• M-shell: 18 electrons

2. Subshells

Subshells are of four types:

• s (spherical shape, 1 orbital, holds 2 electrons)
• p (dumbbell-shaped, 3 orbitals, holds 6 electrons)
• d (5 orbitals, holds 10 electrons)
• f (7 orbitals, holds 14 electrons)

Electrons fill these subshells according to increasing energy.

Rules Governing Electronic Configuration

Three major rules determine how electrons are arranged:

1. Aufbau Principle

Electrons fill the lowest available energy level first.
For example, 1s fills before 2s, and 2s fills before 2p.

2. Pauli Exclusion Principle

No two electrons in an atom can have the same set of four quantum numbers.
This means each orbital can hold a maximum of two electrons with opposite spin.

3. Hund’s Rule of Maximum Multiplicity

Electrons occupy orbitals singly before pairing up.
In p, d, or f subshells, electrons fill each orbital one by one to avoid repulsion.

Examples of Electronic Configuration

1. Hydrogen (Atomic number 1)

Electrons = 1
Configuration = 1s¹

2. Carbon (Atomic number 6)

Electrons = 6
Configuration = 1s² 2s² 2p²

3. Neon (Atomic number 10)

Electrons = 10
Configuration = 1s² 2s² 2p⁶
(Complete outer shell → chemically inert)

4. Sodium (Atomic number 11)

Electrons = 11
Configuration = 1s² 2s² 2p⁶ 3s¹
(One valence electron → highly reactive metal)

These examples show how electronic configuration affects chemical behaviour.

Relationship Between Electronic Configuration and Periodic Table

The periodic table is structured based on electronic configurations:

• Group number often represents valence electrons
• Period number indicates the highest occupied shell
• s-block, p-block, d-block, and f-block depend on the subshell being filled

For example:

• Alkali metals (like Na, K) have 1 electron in their outermost s-orbital.
• Noble gases (like Ne, Ar) have completely filled shells, making them inert.

Electronic configuration helps explain trends such as atomic radius, ionization energy, electronegativity, and metallic character.

How Electronic Configuration Determines Chemical Behaviour

The valence electrons determine:

• Whether an atom will lose or gain electrons
• The type of ion formed
• The number of bonds an atom can make
• Whether the element is metal or non-metal

For instance:

• Sodium loses 1 electron → Na⁺
• Chlorine gains 1 electron → Cl⁻
• Carbon shares 4 electrons → forms covalent bonds

Thus, electronic configuration forms the basis of chemical bonding.

Conclusion

Electronic configuration is the systematic arrangement of electrons in an atom’s shells, subshells, and orbitals. It follows principles like Aufbau’s rule, Pauli Exclusion Principle, and Hund’s Rule. This arrangement helps explain an element’s chemical properties, its position in the periodic table, and how it forms bonds. Understanding electronic configuration is essential for learning atomic structure and the behaviour of elements in chemical reactions.