6s2 + 40s - 60 = 2(3s2 + 20s - 30)
[Xe] Normally the electronic configuration for Barium would be [Xe] 6s2, but since you want it for Ba2+, you're missing two electrons. You get rid of the 6s2 and get [Xe].
[Xe] 6s2 4f14 5d10 6p3
Europium
Barium (Ba)
the long hand configuration of Ta (Tantalum, Atomic # 73) is: (be patient, its LONG) 1s2 2w2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d3 *this is including the Aufbau Principle. Save
The electron configuration of lead is [Xe] 4f14 5d10 6s2 6p2.
The GCF is s.
[Xe]6s2
Electronic configuration of hafnium: [Xe].4f14.5d2.6s2 And in simpler form 2, 8, 18, 32, 10, 2
[Xe] 4f14 5d10 6s2 6p2
All alkaline earth metals have electron configurations ending in s2; 6s2 would be the alkaline earth metal in period 6 of the PTE, which is barium.