Why electronic configuration is not 5d5 6s1?!.. (as in case of Cr & Mo)..
Dear Student
W has atomic no. of 74 with electronic configuration [Xe] 4f14 5d4 6s2.
Now. due to the f-orbitals this period elements show lanthanide contraction. Thus, Mo and W have almost similar radius with tungsten having high effective nuclear charge than Mo. Due to this the instability due electron electron repulsion in W (if 5d5 6s1) will outweigh the stabilty due to half-fiiled d-orbital (as in case of Cr and Mo). Thus, W show unique configuration than it's group.
W has atomic no. of 74 with electronic configuration [Xe] 4f14 5d4 6s2.
Now. due to the f-orbitals this period elements show lanthanide contraction. Thus, Mo and W have almost similar radius with tungsten having high effective nuclear charge than Mo. Due to this the instability due electron electron repulsion in W (if 5d5 6s1) will outweigh the stabilty due to half-fiiled d-orbital (as in case of Cr and Mo). Thus, W show unique configuration than it's group.