Question

Out of 6s and 4f orbitals, which is filled first and why?

Answer 1

• Lowest energy orbitals fill first. Thus, the filling pattern is 1s, 2s, 2p, 3s, 3p, 4s, 3d, etc. Since the orbitals within a subshell are degenerate (of equal energy), the entire subshell of a particular orbital type is filled before moving to the next subshell of higher energy.
  
• The orbitals are filled according to (n+l) rule i.e. the orbitals having more (n+l) value will be filled before even if the value of n of that particular orbit is more.
• Here, (n+l) of 6s orbital is 6 and that of a 4f orbital is 7 and hence 4f orbital is filled before 6s orbital.