Explain actinoid contraction.

Hint:You should know that all actinoid are typical metals, which are very soft and have a silvery color which naturally tarnishes in air. Generally contraction means becoming smaller, shorter or broader.

Complete step by step answer:
-Generally all actinoid or actinides are 15 consecutive chemical elements present in the periodic table. They are nothing but chemically similar metallic elements with atomic numbers ranging from 89 to 103. They include fifteen elements starting from Actinium (Ac) and further include Thorium (Th), Protactinium (Pa), Uranium (U), Neptunium (Np), Plutonium (Pu), Americium (Am), Curium (Cm), Berkelium (Bk), Californium (Cf), Einsteinium (Es), Fermium (Fm), Mendelevium (Md), Nobelium (No), and Lawrencium (Lr). In the periodic table, the series is located under the lanthanide series, which is present underneath the main body of the periodic table.
-The lanthanide series can be found naturally on Earth.
-So, Let us see what actinoid contraction is.
- Generally when we talk about actinoid, there is a gradual increase in atomic size, atomic radii or ionic radii. Now when we talk about actinoid contraction, it refers to the gradual decrease in the atomic size, atomic radii or ionic radii.
-More specifically, the size of the atom regularly along the actinides series with increase in atomic number from Th to Lr. The steady decrease in ionic radii with an increase in atomic number is referred to as actinide contraction.
-This actinoid contraction is caused because of the imperfect shielding by 5f-electrons. As we can see that the atomic number increases, and even the inward pull experienced by 5-f electrons also increases.

Note: On a very general basis Actinium, thorium, protactinium, and uranium are the only actinoid elements found in nature. The remaining actinoid elements, commonly called the transuranic elements.