Question

Why does basicity decrease across a period in lanthanides?

Answer 1

As we move down the group size of element increase. As a result of it, M-OH ... Why does a basic character increase down the group?

Answer 2

Electronegativity increases as we go across a period and up a column in the period table. Bases donate electrons to form new covalent bonds; therefore if they have a greater attraction for electrons they are less likely to share them. As a result we see that electronegativity is related to basicity.