Electron Configuration of Cobalt (Co)

Orbital Filling Order

Following the aufbau principle, the 27 electrons in Cobalt 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 (7 electrons), then 4s (2 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 Cobalt match the configuration of Ar. This allows us to abbreviate the configuration as [Ar] 3d⁷ 4s², where [Ar] represents the filled core and the remaining entries show the valence electrons.

Valence Electrons

The valence shell of Cobalt contains 7 electrons in the 3d subshell and 2 electrons in the 4s subshell. These outermost electrons determine Cobalt's chemical reactivity, bonding behavior, and position in the periodic table as a d-block element in period 4.

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