Question 23 - Past Year - 3 Mark Questions - Chapter 5 Class 10 - Periodic Classification of Elements

An element ‘X’ belongs to 3rd period and group 16 of the Modern Periodic Table.

(a) Determine the number of valence electrons and the valency of ‘X’.

(b) Molecular formula of the compound when ‘X’ reacts with hydrogen and write its electron dot structure.

(c) Name the element ‘X’ and state whether it is metallic or non-metallic.

Answer

X belongs to the 3rd period. So, it has 3 shells.

X belongs to the 16th group.

Group number = 10 + number of valence electrons 

16 = 10 + number of valence electrons

Number of valence electrons = 16 - 10 = 6

Valency = 8 - 6 = 2

(a)  

Number of valence electrons of X = 16 - 10 = 6

Valency of X = 8 - 6 = 2

(b)

X has a valency of 2 and Hydrogen has a valency of 1 so the formula of the compound formed by them will be H 2 X

Electron dot structure of H ₂ X:  

(c)

The element X is sulphur.

  Metals lose electrons to become stable whereas, non-metals gain electrons to become stable.

Sulphur gains electrons to become stable. Hence it is a non-metal.