The Actinides

These elements are also called second inner transition elements as the 5f orbital which is inner to 6d is getting filled with electrons. The 5f series starts from the element thorium and ends with lawrencium with a total of 14 elements. The series starts after the transition element actinuim (Ac) 6d ¹7s² which resembles in properties with 5f series therefore, it is taken as a parent element and hence, the name actinides was coined.