Question

What period are lanthanides?

Answer 1

Lanthanides are also known as rare earth elements of the modern periodic table the name rare earth elements is due to occurrence of these elements which is very small and deep buried inside the earth crust and these are available in monazite sand as lanthanide orthophosphates.

Complete step-by-step answer: As we know our periodic table is divided into 4 group elements known as s, p, d and f block elements. In f block elements two types of elements are present which are named as lanthanides and actinides with the filling of 4f and 5f outermost shells.
The elements having atomic numbers from 58 to 71 start with the element Lanthanum are known as lanthanides. The lanthanide family contains fifteen metallic elements starting from lanthanum and ending with lutetium all are known as f-block elements except lanthanum as the valence electrons of these elements lie in the 4f orbital. Lanthanum is a d-block element showing an electronic configuration $[Xe]5{{d}^{1}}6{{s}^{2}}$. Lanthanum basically belongs to the 6th period and 15th group of periodic tables. These metals are highly dense in nature and have very high melting and boiling points. Common oxidation state of lanthanides is +3.
Thus from the above discussion we can conclude that lanthanides belong to the 6th period.

Note: All elements in lanthanides have a luster and silver in color, soft metals and can be cut with a knife, these metals mostly form trivalent compounds but sometimes can also form divalent or trivalent compounds. These also have different reaction tendencies depending on basicity.