Question

Calcium (atomic number 20) has electron configuration 1s2,2s2,2p6,3s2,3p6,4s2. the atomic number of scandium is 21. which orbital does the 21st electron enter?

a.3d
b.4p
c.4d
d.4f

Answer 1

if you look at the periodic table, you can see that Sc is in the transitional group metals, so it should have d orbital,
also it is in 4th period, so it has 3d orbital
and 21 st electron enters 3d orbital
Answer a.3d
after 4s electrons go into 3d -orbital