Ar3d8

Ar3d8 is a shorthand notation for the electron configuration [Ar] 3d8, indicating eight electrons in the 3d subshell beyond the argon core. In inorganic chemistry and atomic physics, this configuration is most commonly associated with the nickel(II) ion (Ni2+), which results from removing two electrons from neutral nickel (Ni).

In Ni2+, the 3d subshell contains eight electrons, giving rise to characteristic magnetic and spectroscopic properties. The free Ni2+ ion has a ground term often cited as 3F, and when Ni2+ adopts common coordination geometries, the d-electron arrangement is frequently described in crystal-field terms as t2g^6 eg^2 in an octahedral field. This leads to two unpaired electrons and a spin state of S = 1, rendering many Ni2+ complexes paramagnetic with a spin-only magnetic moment near 2.8 Bohr magnetons (orbital contributions can modify this value somewhat).

Nickel(II) complexes that exhibit Ar3d8 behavior commonly display colors arising from d–d transitions, with hues ranging from blue to green depending on the ligands. The geometry of Ni2+ complexes varies with the ligand environment: octahedral is common, but strong-field ligands can stabilize square-planar Ni2+ structures, which often differ in magnetic behavior compared to their octahedral counterparts.

Overall, Ar3d8 serves as a concise way to denote the eight 3d electrons in Ni2+ and is a useful reference point in discussions of nickel chemistry, transition-metal spectroscopy, and coordination chemistry.