General Chemistry I: Quantum Numbers & Electron Config

Study Notes

General Chemistry I - Lecture Notes

Course title: General Chemistry I
Instructor: Dr. Mahmoud A. A. Ibrahim
Department: Chemistry, Faculty of Science, Minia University
Email: [email protected]
Course code: CH101

Lecture 2: Quantum Numbers & Electron Configuration

Topic: Quantum Numbers
- Each electron in an atom is described by four quantum numbers.
- Principle quantum number (n): Specifies the energy level and size of the electron's orbital (positive integer, excluding zero).
- Angular quantum number (l): Specifies the shape of the electron's orbital. It also affects the subshell energy (integers from 0 to n-1). Subshells are labelled s, p, d, f (s=0, p=1, d=2, f=3).
- Magnetic quantum number (ml): Specifies the orientation of the orbital in space(-l to +l). Determines the number of orbitals in each subshell (2l + 1 orbitals) The s subshell has 1 orbital, the p subshell has 3, the d subshell has 5, and the f subshell has 7.
- Spin quantum number (ms): Specifies electron spin (equal to +1/2 or -1/2). Electrons in the same orbital must have opposite spins.
Topic: Pauli Exclusion Principle
- No two electrons in an atom can have the same set of four quantum numbers.
- No more than two electrons can occupy the same atomic orbital.
- Electrons within the same orbital must have opposite spins.
Topic: Electron Configuration
- Aufbau principle: Electrons fill orbitals in increasing order of energy levels (1s, 2s, 2p, 3s, 3p...).
- The distribution of electrons among the orbitals of an atom is called the electron configuration.
- Orbital diagrams: Diagrams that show the electron placement in each orbital within a subshell
- Hund's rule: Electrons occupy orbitals of equal energy singly before they pair up.
Topic: Abbreviated Electron Configurations
- Abbreviated electron configurations use the noble gas preceding that element, followed by the electron configuration of the remaining electrons.
Topic: Valence Shell Electron Configuration
- Configuration focusing on the outer shell electrons (valence shell)
Topic: Unexpected Electron Configurations
- Some elements have unexpected electron configurations (e.g., Cr and Cu). This is due to special stability that arises when specific subshells are half-filled or completely filled.