Actinides
After lanthanum, thus the name.
Actinides comprise of atomic number 90-103. They are placed at bottom of periodic table.
The f-block elements are placed at the bottom of the periodic table because if they were placed where they belong the periodic table would be too big to fit on a normal sheet of paper.
At the bottom of the Periodic Table
elements 56 through 71 are called the lanthanoids
The elements that are placed outside of the periodic table are called transactinides. These elements are usually placed in a separate row below the main table and are synthetic elements that do not occur naturally on Earth.
Astatine is placed in group-17 in the Periodic Table. Its symbol is At.
Compounds are not placed in the periodic table.
Actinoids are placed in a separate row under the periodic table.
If new elements are placed, then they would be appended in the periodic table. It won't disturb existing periodic table.
CO3 is not placed in periodic table. Only elements are arranged in periodic table.
Metals are placed at the left. Non-metals are placed at right in periodic table.