Basicity of hydrides if group 15 elements

[AdityaDev]

For group 15 elements the order of basicity given is
NH3 > PH3 > AsH3 > SbH3 > BiH3
And order of reducing strength is
BiH3 > sbH3 > AsH3 > PH3 > NH3

Why are they in opposite order? Reducing nature means tendency to donate electrons. Basicity means strength of bases and hence as basicity increases, the basic nature increases which means tendency to donate electrons increases. Then shouldn't they be in same order?

 

[Bystander]

Reducing nature means tendency to donate electrons.

Reducing agents do not "donate" electrons in a redox reaction; they lose electrons to oxidizing agents.

 

[AdityaDev]

Reducing agents do not "donate" electrons in a redox reaction; they lose electrons to oxidizing agents.

Fine. But still they lose electrons.

 

[Bystander]

Lose, not loan. As bases they get them back, they are recoverable.

 

[AdityaDev]

Lose, not loan. As bases they get them back, they are recoverable.

Ok. Now what about the order?

 

[Bystander]

order?

"I'll take a burger and fries, thank you."
You have to do some of the work. What do you know about the physical and electronic properties of Group V?

 

[AdityaDev]

"I'll take a burger and fries, thank you."
You have to do some of the work. What do you know about the physical and electronic properties of Group V?

" do you want chicken burger or veg burger?"
Configuration ns2 np3
Half filled orbitals - more stabs than group 6
Nitrogen exists as N2 because of its ability to form p$\pi$ - p$\pi$ overlapping. Other g5 elements have less or no tendency for such bonds.
Phosphorous exits as white, red or black. White P is reactive.
(Other elements not in syllabus)
Nitrogen is a bit different because it lacks d orbitals.

NH3 is formed by haber's process or by thermal decomposition of NH4Cl (other anions are carbonate and sulphate).
PH3 is formed when White P4 reacts with NaOH or by reacting PH4I with KOH. PH3 can also be formed by reacting Ca3P2 with water or HCl.
Both ammonia and PH3 are basic.
Should I explain more?

 

[Bystander]

Covering some of the chemistry works. How does the strength of the bond between hydrogen and the group V elements change as you move down the column?

 

[AdityaDev]

Covering some of the chemistry works. How does the strength of the bond between hydrogen and the group V elements change as you move down the column?

Decreases

 

[Bystander]

And, hydrogen is a fairly good reducing agent, is it not? And, if hydrogen is more easily released from a compound, it (the compound) is a stronger, or weaker reducing agent?

 

[AdityaDev]

Reducing nature increases if hydrogen is released easily

 

[Bystander]

Correct. Did you wish to look further at the "basicity" question?

 

[AdityaDev]

What is the difference between basicity, basic strength and reducing nature?

 

[AdityaDev]

So you say basicity is the removal of hydrogen?

 

[Bystander]

I hate to use analogies; basicity/base strength is to reducing nature/strength as your eye color is to your shoe size --- knowledge of one tells you nothing about the other.

So you say basicity is the removal of hydrogen?

No. Hydrogen is a reducing agent. It is more freely available (more weakly bound) in BiH₃ than in ammonia, and therefore BiH₃ is the stronger reducing agent.
Ammonia is the smaller molecule, and the lone pair electrons are a more prominent feature of the molecule, and have no significant possibilities of being stabilized within the molecule by exchange (or jumping) around the additional d, and f orbitals that are at much lower energies in the heavier members of the family. They, therefore, can share ("donate") more strongly/easily with acidic species (H⁺, AlCl₃, BH₃).

 

[Usd95]

For group 15 elements the order of basicity given is
NH3 > PH3 > AsH3 > SbH3 > BiH3
And order of reducing strength is
BiH3 > sbH3 > AsH3 > PH3 > NH3

Why are they in opposite order? Reducing nature means tendency to donate electrons. Basicity means strength of bases and hence as basicity increases, the basic nature increases which means tendency to donate electrons increases. Then shouldn't they be in same order?

As found in J.D.Lee's inorganic chemistry book