What is the first element of the actinides?

The first element in the actinide series is actinium , a chemical element in the Periodic Table that has the symbol Ac and atomic number 89.

The actinide (or actinoid) series encompasses the 15 chemical elements that lie between actinium and lawrencium on the periodic table , with atomic numbers 89-103.

The actinides get their name from the first element in the series , actinium.