Question

Write one similarity and one difference each between the chemistry of lanthanide and actinide elements.

Answer 1

Think about where all these elements are placed in the periodic table, the configuration of their outermost orbit and other properties that are usually attributed to placement in the periodic table.

Complete answer:

Similarities:
One of the major similarities between lanthanide and actinide elements in the periodic table is that all of them are f-block elements. While lanthanides lie in period 6, actinides can be found in period 7.
They have the valence shell of (n-2)f.
In both these series of elements, the ionic and atomic size decreases as we go further down the period.
The most commonly found oxidation state in all the f-block elements is +3 and all are highly electropositive elements.
Differences:
The major differences between lanthanides and actinides are

Lanthanides	Actinides
All except Promethium (Pm) are not radioactive.	All are radioactive
Most form colourless compounds	Most form coloured compounds
Found in period 6	Found in period 7
Involved in filling of 4f orbital	Involved in filling of 5f orbital
More are found naturally	Less are found naturally
Do not form complexes	May form complexes

Note: Do not get confused about the presence of the elements Lanthanum(La) and Actinium(Ac) in their respective sets of elements. Although their location is shown to be in the d-block in the periodic table, they belong to the set of f-block elements and are the elements that the sets are named after.