Question

The elements with atomic number 117 and 120 are yet to be discovered. In which group would you place these elements when discovered?
(A) 17, 2
(B) 16, 4
(C) 15, 3
(D) 18, 2

Answer 1

Hint :To know about the group of an element the electronic configuration of its element has to be known, the electronic configuration of element with atomic number 117 will be $ \left[ Rn \right]5{{f}^{14}}6{{d}^{10}}7{{s}^{2}}7{{p}^{5}} $ and that of the element with atomic number 120 will be $ \left[ Og \right]8{{s}^{2}} $ .

Complete Step By Step Answer:
The element with atomic number 117 will be placed in the 17th group of the periodic table and the element with atomic number 120 will be placed in the 2nd group of the periodic table.
Electronic configuration of these elements are $ \left[ Rn \right]5{{f}^{14}}6{{d}^{10}}7{{s}^{2}}7{{p}^{5}} $ and $ \left[ Og \right]8{{s}^{2}} $ respectively.
Now looking at the electronic configuration of an element with atomic number 117, we can say that its f, d and s orbitals are completely filled. Only the p orbital is lacking one electron to become stable, thus it is placed in the p block of elements.
As it is not stable, to calculate its group we have to add the number of electrons in p orbital and s orbital with 10, thus the group which it will be placed in is 17.
For the element having atomic number 120, the electronic configuration shows that its 8th s orbital is filled completely; thus, it is placed in the s block of the periodic table. And thus it is placed in the 2nd group of the periodic table.
Thus, the elements with atomic number 117 and 120 are placed in the 17th and 2nd group respectively.
The correct answer is option A, 17 and 2.

Note :
The electronic configuration of elements with atomic number 117 and 120 are written like this because it is easily understandable. $ Rn $ in the electronic configuration of element with atomic number 117 represents Radon which has atomic number 86, and $ Og $ in the electronic configuration of element with atomic number 120 represents Oganesson, which has atomic number 118. Oganesson is also known as ununoctium.