What are the two rows placed at the bottom of the periodic table?

The two rows present at the bottom of the periodic table together form the Inner Transition elements of the periodic table. The inner transition elements in the periodic table are a part of the transition metals, which range from the third to the twelfth group of the periodic table. The two rows placed at the bottom of the periodic table are the two series of elements, the Lanthanide series and the Actinide series.


Lanthanide series
The elements in the upper row form the Lanthanide series of elements, since the first element in the row is Lanthanum. Lanthanum is placed in the third group in the sixth column of the periodic table. It is the first element of the Lanthanide series, and the rest of the elements are present in the first row at the bottom of the periodic table.

Actinide series
The elements in the lower row form the Actinide series of elements. They are named so, because the first element of this series is Actinium. This element is placed in the third group in the seventh row of the periodic table. The rest of the elements of the Actinide series are placed in the second row at the bottom of the periodic table.

Why are the two rows placed at the bottom of the periodic table?
The two rows of elements are placed at the bottom of the periodic table in order to not distort th shape of the periodic table. These elements are more than what can be placed in a single row in the periodic table. If they would be placed in the periodic table, this would cause the shape of the periodic table to become highly distorted. This is because all the elements in each of the two rows belong to one particular group - the elements of the first row, that is the Lanthanide series elements, belong to the third group of the periodic table, and so do the elements of Actinide series.

Important points about the elements in the two rows at the bottom of the periodic table.

• These elements are combined known as the Rare earth metals along with the two more element present in their group - Scandium and Yttrium.
• These elements are all radioactive in nature. See here : "What are radioactive elements?"
• These elements all belong to the third group of the periodic table.
• These elements are called the Inner Transition elements, or the Inner Transition metals.