Question

Assertion :(A) : Alkali metals are soft and have low melting and boiling points. Reason: (R) : This is because interatomic bonds are weak.

• A. Both (A) and (R) are not true
• B. (A) is true but (R) is not correct explanation of (A)
• C. (A) is true but (R) is ture
• D. Both (A) and (R) are true and (R) is correct explanation of (A)

Answer 1

The correct option is D Both (A) and (R) are true and (R) is correct explanation of (A)

As you go down any group, there are extra electron shells (for example Lithium has 2 shells, Francium has 7) which cause electron shielding. Because the force of attraction must extend further and through these shells to the outermost shell, the force becomes less so there is less strong bonding occuring.

Thus, it is easier to break these less strong bonds, and because the melting point is a measure of the point at which all the bonds holding a metallic structure together are broken, it will decrease because this point is reached a lot sooner as the bonds are not as strong.

Hence , we can say, All alkali metals are found to be very soft and they have low melting and boiling points. Alkali metals have low binding energy in the metal crystal lattice as these atoms have only one valence electron. This results in the formation of metallic bonds which are not very strong. Also, alkali metals melting and boiling points decrease down the group.