Which of the following is true regarding the inner transition elements? (pf)

a. these include the lanthanides and actinides and do not have f sublevels.
b. they occupy the d block of the periodic table.
c. these include all elements in groups 3-12.
d. their valence electrons can be located in both s and f sublevels.

The answer is D

Explanation:

The inner transition elements are those in the two long rows at the bottom of the Periodic Table.

The lanthanide series starts after Ba in Period 6, and the actinide series starts after Ra in Period 7.

Thus, we would predict their electron configurations to be of the form

However, the energy levels of the ns, (n-1)d, and (n-2)f orbitals are so close in energy that there are many exceptions to our predictions

For example, here are some electron configurations.

La = [Xe]6s²5d (not [Xe]6s²4f)

Ce = [Xe]6s²4f5d (not [Xe]6s²4f²)

Pr = [Xe]6s²4f³ (as predicted)

Thus, their valence electrons can be in both s and f (and sometimes d) sublevels.

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