where is the lanthanide placed in the periodic table?
The periodic table is divided into s,p,d and f block elements.The electronic configuration of lanthanides and actinides is (n-2)f1-14 (n-1)d0-1 ns2.As the 4f orbital starts and completes its filling from atomic number 57 to 71, it covers all the elements from cerium to lutecium.Similarly, 5f orbital covers elements from atomic number 90 (thorium) to 103(lawrencium).These two series together form f block of the periodic table and hence are placed separately in the periodic table.