Question

The elements A, B, C, D and E have atomic number 35,11,17,12 and 13 respectively. Which pair of elements belong
to the same group?​

Answer 1

The elements with atomic number 35 and 17.

Given:

(i) The elements A, B, C, D and E have atomic number 35,11,17,12 and 13 respectively.

To find:

The pair of elements belong to the same group.

Solution:

The simple logic behind this is that the elements having the same number of electrons in the last shell fall under the same group.

The element whose atomic number is 35, its electronic configuration can be written as:

2,8,18,7       (Valence electrons = 7)

For 11, it is :

2,8,1             (Valence electrons = 1)

For 17, it is :

2,8,7            (Valence electrons = 7)

For 12 it is :

2,8,2           (Valence electrons = 2)

For 13 it is :

2,8,3            (Valence electrons = 3)

Clearly, the elements with atomic number 35 and 17 fall under the same group (17) as the have same number of valence electrons, 17.