Electron Configuration of Selenium (Se)

Orbital Filling Order

Following the aufbau principle, the 34 electrons in Selenium fill orbitals in order of increasing energy: 1s (2 electrons), then 2s (2 electrons), then 2p (6 electrons), then 3s (2 electrons), then 3p (6 electrons), then 3d (10 electrons), then 4s (2 electrons), then 4p (4 electrons).

Each orbital is filled according to the Pauli exclusion principle (at most 2 electrons per orbital) and Hund's rule (electrons occupy degenerate orbitals singly before pairing).

Noble Gas Shorthand

The inner electrons of Selenium match the configuration of Ar. This allows us to abbreviate the configuration as [Ar] 3d¹⁰ 4s² 4p⁴, where [Ar] represents the filled core and the remaining entries show the valence electrons.

Valence Electrons

The valence shell of Selenium contains 10 electrons in the 3d subshell and 2 electrons in the 4s subshell and 4 electrons in the 4p subshell. These outermost electrons determine Selenium's chemical reactivity, bonding behavior, and position in the periodic table as a p-block element in period 4.

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