ELECTRONIC CONFIGURATION
3.7 Electronic Configuration
Shells
Definition
Based on Bohr's atomic theory, shells are circular paths where electrons revolve around the nucleus. Each shell has fixed energy, described by the quantum number n (n = 1, 2, 3, ...). As n increases, the distance from the nucleus and the energy of the shell increase.
Nomenclature
- n = 1: K shell
- n = 2: L shell
- n = 3: M shell
Sub-Shells
Definition and Distribution
Sub-shells are subdivisions of shells or energy levels. They are represented by combining the n value and sub-shell symbol.
- K shell (n = 1): 1s
- L shell (n = 2): 2s, 2p
- M shell (n = 3): 3s, 3p, 3d
- N shell (n = 4): 4s, 4p, 4d, 4f
Electron Capacity and Energy Order
- s sub-shell: 2 electrons
- p sub-shell: 6 electrons
- d sub-shell: 10 electrons
- f sub-shell: 14 electrons
Energy order: 1s < 2s < 2p < 3s < 3p < 4s < 3d ...
Electronic Configuration
Definition
Electronic configuration refers to the arrangement of electrons in sub-shells. It follows the Auf Bau Principle, which states that electrons fill the lowest energy sub-shells first.
Symbols for Atoms and Ions
Format: [Mass number][Element symbol][Charge][Atomic number]. For example: Mg12242+ (Magnesium with mass number 24, charge +2, atomic number 12).
Key Points
- Rutherford's planetary model: Nucleus (protons) surrounded by electrons.
- Bohr's model: Electrons in fixed circular orbits (shells).
- Isotopes: Atoms with the same number of protons but different numbers of neutrons.
- Uranium isotope: Used in nuclear reactors and atomic bombs.
- Radioactive isotopes: Various applications in science and medicine.
- Electronic configuration: Arrangement of electrons in sub-shells.
- Auf Bau Principle: Electrons fill lowest energy levels first.
References
- B. Earl and LDR Wilford, "Introduction to Advanced Chemistry"
- Iain Brand and Richard Grime, "Chemistry (11-14)"