What are lanthanides and actinides?

Explanation

• In 4f series, 4f orbitals are being progressively filled with electrons, `4f^(1-14)5d^(0-1)-6s^(2)`. These elements lie in 6th period and are called rare earths or lanthanides or lanthanones.
• In 3f series, 5forbitals are being progressively filled with electrons, `5f^(1-14)6d^(0-1)-7s^(2)` These elements lie in 7th period and are called actinides or actonones.