Choose an element from period 3 of modern periodic table that matches the

description given below in each instance. Give reason for your choice.

a. It has a similar structure to diamond.

b. It has same valency as Lithium.

c. It has variable valency and is a member of the Oxygen family (group 16).


We know that third period of Periodic table has 8 elements

Sodium (Na), Magnesium (Mg), Aluminium (Al), Silicon (Si), Phosphorus (P), Sulfur (S), Chlorine (Cl),and Argon (Ar).

as shown below

Periodic table of elements-01-01.jpg

Out of this,

a. Silicon has similar structure to Diamond


We know that, Diamond is an allotrope(form) of Carbon

And Carbon and Silicon are similar because fo following reasons

Both have Valency of 4 (Tetravalent)

Both form covalent bonds

Both do Catenation (ability to self combine and form long chain)

Both have tetrahedral structure (Each atom is joined by 4 other atoms)


b. Sodium has same valency as Lithium


We know that

Lithium has Valency of 1

Sodium also has Valency of 1 (Lies in first period(

Hence, Answer is Sodium


c. It has variable valency and is a member of the Oxygen family (group 16).


Oxygen Family refers to chemical elements lying in Group 16

These include elements like

Oxygen, Sulphur, Selenium, Tellurium and Polonium

All these have 6 electrons in outermost shell

Out of this, Sulphur lies in third period

Valency of Sulphur

Sulphur has 6 electrons in outermost shell, so it needs 2 more to become stable

hence, Valency of Sulphur is 2

However, sometimes it shows Multiple Valencies also


In Case of SO2,It shows Valency of 4


In Case of SO3,I shows Valency of 6


Hence, Sulphur is a Metal which belongs to Oxygen Family (Group 16) and has multi valency and belongs to O

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