Question

What are chemical twins? Write two example

Answer 1

Chemical twins are those in which the properties of some elements are same. Atomic size of Zr and Hf , Nb and Ta are similar. This is due to Lanthanide contraction.
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Answer 2

Chemical twins:

Chemical twins are elements who are similar in nature due to the very close atomic size. The similarity or closeness in atomic size is not the same or close atomic number but some special reasons like lanthanide contraction. The shielding effect of 4f electrons is poor which results in Lanthanide contraction.

Two examples of chemical twins are:

a)  Zirconium (Zr - atomic number 40) and Hafnium (Hf - atomic number 72)

b)  Niobium (Nb - atomic number 41) and Tantalum (Ta - atomic number 73)