D and F blockWatch
Why don't you just google.
(My all time favourite website now that ceilingcat.com is no more)
As you proceed across each row in the periodic table, Zeff increases.
The amount by which Zeff increases depends on the shielding ability of the energy levels being filled as you proceed across a row. If the additional electrons are poor at shielding the increase in nuclear charge, then the effective nuclear charge will increase a lot, if shielding is effective, then Zeff increases by only a small amount.
Across the Lanthanides the nuclear charge increases by 14 units, but the 4f orbitals have no radial maximum close to the nucleus in their electronic radial distributions functions (you should be familiar with RDF's) and so are particularly poor at shielding. This means that Zeff increases quite rapidly across the Lanthanide series. This increased Zeff leads various effects in the properties of elements. For example:
- The radii of lanthanide's decrease almost linearly across the period.
- The radii of the elements following the lanthanides are reduced compared to what might be expected, so third row transition metals have similar radii and properties to second row transition metals.
- The lanthanide contraction is in part responsible for the so called alternation effect in the main group
Most of that information is pretty clearly presented on the wikipedia article. Presuming you are at university, you really should be comfortable with reading numerous sources until you understand something. Googling Lanthanide contraction gives numerous links (some of which give a clearer explanation than wikipedia in my opinion) and by using all of those I think you should have been able to work it out for yourself. Failing that, good explanations may be found in numerous inorganic texts.