What is the major difference between lanthanides and actinides?

Answer 1

Generally speaking, the lanthanides are naturally occurring and stable, although relatively uncommon. The actinides are naturally occurring through uranium; after that, they're synthetic, and all are unstable (radioactive.)

Answer 2

The major difference between these two groups is that most of the actinides are not naturally occurring, since they are radioactive with very short half-lives. Lanthanides, also know as the Rare Earth Elements, are due to the filling of the 4f orbital shell and actinides are due to the filling of the 5f orbital shell. Since neodymium and uranium are in the same column of the (combined) lanthanide/actinide rows, they should have similar properties. I am sorry if this answer is to technical for you, but science is technical.

Answer 3

The major difference between lanthanides and actinides is their position in the Periodic Table. Lanthanides are located in the f-block beneath the main body of the periodic table, while actinides are located in the f-block below the lanthanides. Additionally, lanthanides have filled f-orbitals from 4f1 to 4f14, while actinides have filled f-orbitals from 5f1 to 5f14.