## Chemistry and Chemical Reactivity (9th Edition)

Y has a configuration $[Kr]\ 4d^1\ 5s^2$, La, $[Xe]\ 5d^1\ 6s^2$ and Lu, $[Xe]\ 4f^{14}\ 5d^1\ 6s^2$. Both have very similar electronic configurations, differing by the 4f subshell filled in Lu, but by definition La should be below Y since it has exactly the same configuration.