Question

While studying the periodic properties, Arti came across an abnormal be haviour in the atomic size of HF. She found that, even though HF is placed below Zr in the same group, both have almost similar atomic sizes.
(I) Which phenomenon is responsible for the above behaviour? Define it

Hint:

Lanthanide contraction is significant because it leads to unexpectedly similar atomic sizes across periods, affecting elements such as HF and Zr

Answer 1

The phenomenon responsible for the above behaviour is Lanthanide Contraction. This con traction refers to the gradual decrease in the size of the atoms and ions of the lanthanide series elements as the atomic number increases. This happens because the 4f-electrons, which are added as you move across the lanthanide series, do not shield the nuclear charge effectively. This causes the effective nuclear charge to increase, resulting in a decrease in the atomic size. The lanthanide contraction affects the atomic sizes of elements in subsequent periods, leading to similar sizes for elements like HF and Zr, which are in the same group.