Question

Reason of lanthanide contraction is:
(A) Negligible screening effect of f orbital
(B) Increasing nuclear charge
(C) Decreasing nuclear charge
(D) Decreasing screening effect

Answer 1

Hint: Victor Glodschmidt gave the term Lanthanide contraction in 1925. There are a total of 15 elements in the lanthanide series and these show the same peculiar properties such as decrease in the ionic radius.

Complete step by step solution:
Lanthanide contraction is the abnormal decrease in the ionic and the atomic radius with the increase in the atomic number. The elements from atomic number 57 to 71 i.e. from lanthanum to lutetium come under the lanthanoid contraction. The cause of lanthanide contraction is the poor shielding effect of the 4f orbital due to which the electrons in the s orbital attract more towards the nucleus which leads to the decrease in size of the atom.
The elements of the lanthanoid series which is considered as the hardest substance is lutetium and it also has a high melting point. As the nuclear charge increases, the valence shell is pulled slightly towards the nucleus of the atom.

Hence the correct answer is option (A) negligible screening effect of the f orbital.

Note: Due to the decrease in the atomic radii of the lanthanoid, it is observed that the basicity of the elements also decrease because of the increase in the covalent bond between the atoms which is according to the Fajans rule. Due to the decrease in the atomic radii, the ionization energy as well as the electronegativity increases. Because the atomic radii is inversely proportional to the ionization energy and electronegativity. They are hard to separate because of the strong attachment of the outermost electrons with the nucleus.