Electronic Configurations - Class 12 Chemistry
1. Introduction to Electronic Configuration
Electronic configuration refers to the arrangement of electrons in the orbitals of an atom. It follows
specific rules and principles to determine how electrons are distributed among atomic orbitals.
2. Principles Governing Electron Configuration
a) Aufbau Principle
Electrons occupy orbitals in the increasing order of their energy levels. The order is given by the
(n+l) rule.
b) Pauli's Exclusion Principle
No two electrons in an atom can have the same set of four quantum numbers.
c) Hund's Rule of Maximum Multiplicity
Electrons fill degenerate orbitals singly first before pairing occurs, to maximize spin multiplicity.
3. Notations & Rules for Writing Electronic Configurations
Electron configuration is written using subshell notation (e.g., 1s2 2s2 2p6). The periodic table helps
determine configurations based on element position.
4. Electronic Configurations of Elements
Elements are categorized into s, p, d, and f blocks based on their valence electron configurations.
For example:
- Hydrogen: 1s1
- Carbon: 1s2 2s2 2p2
- Iron: [Ar] 3d6 4s2
5. Electronic Configuration of Ions
Cations lose electrons from the outermost shell, while anions gain electrons. Example: Na+ -> 1s2
2s2 2p6 (loses 1 electron from 3s).
1. Introduction to Electronic Configuration
Electronic configuration refers to the arrangement of electrons in the orbitals of an atom. It follows
specific rules and principles to determine how electrons are distributed among atomic orbitals.
2. Principles Governing Electron Configuration
a) Aufbau Principle
Electrons occupy orbitals in the increasing order of their energy levels. The order is given by the
(n+l) rule.
b) Pauli's Exclusion Principle
No two electrons in an atom can have the same set of four quantum numbers.
c) Hund's Rule of Maximum Multiplicity
Electrons fill degenerate orbitals singly first before pairing occurs, to maximize spin multiplicity.
3. Notations & Rules for Writing Electronic Configurations
Electron configuration is written using subshell notation (e.g., 1s2 2s2 2p6). The periodic table helps
determine configurations based on element position.
4. Electronic Configurations of Elements
Elements are categorized into s, p, d, and f blocks based on their valence electron configurations.
For example:
- Hydrogen: 1s1
- Carbon: 1s2 2s2 2p2
- Iron: [Ar] 3d6 4s2
5. Electronic Configuration of Ions
Cations lose electrons from the outermost shell, while anions gain electrons. Example: Na+ -> 1s2
2s2 2p6 (loses 1 electron from 3s).
