electron shells

1. Structure of Electron Shells

Electron shells, also known as principal energy levels, represent regions around an atom's nucleus where electrons are most likely to be found.

• Principal Quantum Number ($n$):

  • Shells are identified by the principal quantum number $n$, where $n = 1, 2, 3, 4, \text{etc.}$ - The shell closest to the nucleus corresponds to $n = 1$ and possesses the lowest energy level.

  • As $n$ increases, the shell is located farther from the nucleus and possesses higher energy.

• Maximum Electron Capacity:

  • The maximum number of electrons that a shell can hold is given by the formula $2n^2$.

  • Shell $n = 1$: holds up to $2(1)^2 = 2$ electrons.

  • Shell $n = 2$: holds up to $2(2)^2 = 8$ electrons.

  • Shell $n = 3$: holds up to $2(3)^2 = 18$ electrons.

  • Shell $n = 4$: holds up to $2(4)^2 = 32$ electrons.

2. Subshells and Orbitals

Each electron shell consists of one or more subshells, which are further divided into atomic orbitals.

• Types of Subshells:

  • $s$ subshell: Contains $1$ orbital, holding a maximum of $2$ electrons.

  • $p$ subshell: Contains $3$ orbitals, holding a maximum of $6$ electrons.

  • $d$ subshell: Contains $5$ orbitals, holding a maximum of $10$ electrons.

  • $f$ subshell: Contains $7$ orbitals, holding a maximum of $14$ electrons.

• Subshell Organization by Shell:

  • Shell $n = 1$: $1s$

  • Shell $n = 2$: $2s, 2p$

  • Shell $n = 3$: $3s, 3p, 3d$

  • Shell $n = 4$: $4s, 4p, 4d, 4f$

3. Electron Configuration and Valence Electrons

• Filling Order (Aufbau Principle):

  • Electrons occupy orbitals of lower energy levels first before filling higher energy levels ($1s \rightarrow 2s \rightarrow 2p \rightarrow 3s \rightarrow 3p \rightarrow 4s \rightarrow 3d$).

• Valence Electrons:

  • Electrons occupying the outermost shell are called valence electrons.

  • Valence electrons determine the chemical properties, bonding behavior, and reactivity of an element.