Question

2. The atomic numbers of elements X, Y, Z are 8, 12, 17 respectively, which of these elements belong to the same period? a. X and Y b. Z and X c. Y and Z d. X, Y and Z​

Answer 1

EXPLANATION.

Atomic no. of X = 8

Electronic configuration = 2,6

Valence electrons = 6

Valency of X=2

Atomic no. of element Y = 12

Electronic configuration of Y = 2,8,2

Valency of Y= 2

Atomic no. of element Z = 17

Electronic configuration of Z = 2,8, 7

Valency of Z=1

The element X and Y have same number of valence electrons and since chemical properties depends on the valence electrons. So, Element X and Y will show similar chemical properties.

Answer: Option a or X and Y

Answer 2

c. Y and Z belong to same period.

1. Element X will have electronic configuration: 2,6
2. Element Y will have electronic configuration: 2,8,2
3. Element Z will have electronic configuration: 2,8,7
4. As we know that, in a periodic table, number of shells remains same across the period. They increase down the group.
5. Hence, to identify elements belonging to same period, we need to find elements with same number of shells, irrespective of valence electrons.
6. X has 2 shells and Y and Z have 3 shells.
7. Thus, Y and Z belong to same group.