# Basicity of hydrides if group 15 elements

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1. Dec 25, 2014

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?

2. Dec 25, 2014

### Bystander

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

3. Dec 25, 2014

Fine. But still they lose electrons.

4. Dec 25, 2014

### Bystander

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

5. Dec 25, 2014

Ok. Now what about the order?

6. Dec 25, 2014

### Bystander

"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?

7. Dec 26, 2014

" 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?

8. Dec 26, 2014

### 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?

9. Dec 26, 2014

Decreases

10. Dec 26, 2014

### 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?

11. Dec 26, 2014

Reducing nature increases if hydrogen is released easily

12. Dec 26, 2014

### Bystander

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

13. Dec 26, 2014

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

14. Dec 26, 2014

So you say basicity is the removal of hydrogen?

15. Dec 26, 2014

### 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.
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).

16. Feb 6, 2015

### Usd95

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

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