Electron Shells and Atomic Orbitals
Electron Shells and Atomic Orbitals
Electron Shells
Shells are named K, L, M, and so on from the innermost shell outward.
The maximum number of electrons in a shell is determined by its principal quantum number using 2n².
The K shell holds 2 electrons (n = 1), the L shell 8 (n = 2), and the M shell 18 (n = 3).
Each electron shell has a specific energy level. The source states that shells closer to the nucleus have higher energy and more distant shells have lower energy.
Electrons closer to the nucleus experience stronger attraction to protons; the attraction decreases with distance. Electrons in outer shells are therefore more readily involved in changes.
Atomic Orbitals
A shell may contain orbitals of several shapes. An s subshell has one spherical orbital, a p subshell has three dumbbell-shaped orbitals, and a d subshell has five orbitals. Each orbital holds two electrons.
Rules for Filling Orbitals
1. Electrons fill lower-energy orbitals first, starting with the 1s orbital.
2. Each orbital holds a maximum of two electrons.
EX.
Helium (He) has atomic number 2. Both electrons occupy the 1s orbital, filling the K shell to form a closed shell.
Oxygen: Atomic Number and Orbitals
Oxygen has atomic number 8 and eight electrons. Two fill the 1s orbital and two fill the 2s orbital. The next three occupy px, py, and pz individually, and the final electron pairs in px. The L shell, which can hold eight electrons, remains unfilled, giving an open-shell configuration.