Trisilyl amine, N(SiH3)3 is planar whereas trimethyl amines N(CH3)3 is pyramidal. Explain why?.

In N(SiH₃)₃, N attains sp2 hydridisation and the lone pair of N is involved in d_pi-p_pi  back bonding by getting itself delocalized on to empty 3d – orbitals of silicon.

But in N(CH₃)₃, N is sp3 hybridised in which three of the hybrid orbitals are used in forming s  - bonds with NH₃ groups, while the lone pair is present in the fourth hybrid orbital. Thus the molecule is pyramidal.

For More deatils click here Back Bond theory:

What is the molecular formula of Borax ?

(A) Na₂[B₄O₃(OH)₄].6H₂O

(B) Na₂[B₄O₅(OH)₄].6H₂O

(C) Na₂[B₄O₅(OH)₄].8H₂O

(D )Na₂[B₄O₆(OH)₂].8H₂O

The structure of Borax is Na₂[B₄O₅(OH)₄].8H₂O.

Hence option (C) is the correct answer for details click on link given below

Tincol or Suhaga:

Three-center four-electron Bridge bond (3C-4e Bond): Structure of AlCl3:

(1) Al₂Cl₆ is neither hypovalent nor hypovalent rather its octet is complete. We will used  MOT here  it cannot act as Lewis acid  due to crowding in spite having vacant d orbital’s   however AlCl₃  act as Lewis acid .

(2) Al₂Cl₆ contains six bonds having two bridge bonds (3c-4e) and four bonds is (3C-4e) bridge bonds are lies perpendicular to plane.

(3) The bond lengths of terminal Al−Cl bonds are shorter (206 pm) while bond length of bridged Al−Cl bonds are longer (221 pm) and also outer bond angle (Cl−Al−Cl) are greater (118) than inner bond angle (Al−Cl−Al).

(4) Maximum six atoms are lies in same plane which four terminal Cl and two aluminium atoms.

(5) AlCl₃ in vapor phase or in non-polar solvent is dimeric Al₂Cl₆ hence sp3 hybridised having 3c-4e bonds.

Related Questions: 

(1) Why aqueous solution of AlCl3 is acidic in nature ?

(2) What happen when aq AlCl3 react with Acid or Base?

(3) Although anhydrous aluminium chloride is covalent but its aqueous solution is ionic in nature. Why?

(4) Why BF3 do not exist as dimer?. Explain.

(5) Why B-F bond length in BF3 is shorter (130 pm) than B-F bond Iength in BF4- (143 pm)?. Explain.

(6) B-F bond length in BF3 is shorter than B-F bond length in (BF4)- why?

(7) When B2H6 is allowed to react with following Lewis bases, then how may given Lewis base form adduct through symmetrical Cleavage of B2H6.

(8) What is product of reaction between diborane (B2H6) and ammmonia (NH3)?

(9) Why methylation of Diborane (B2H6) replace four hydrogen only ?

(10) What is Use of Boric Acid?

(11) What is use of Orthoboric acids?

(12) What is basicity of "Boric acid" ?

(13) Why Boric acid exist in solid state ?

(14) What is structure of solid Ortho Boric acid ?

(15) What is effect of heat on Borax?

(16) What is the structure of trimetaboric acid and trimetaborate ion?

(17) What is the Sodium per borate ,give the structure and its uses?

(18) Why aqueous solution of borax reacts with two moles of acids ?

(19) What is the molecular formula of Borax ?

(20) Why Boric acid become strong acid in the presence of cis 1,2-diol or 1,3-diol ?

(21) Why Borazine is more reactive than benzene towards Electrophic Aromatic substitution reactions ?

(22) Why Borazine (B3N3H6) is also known as inorganic benzene ?.

(23) Four-center two-electron bond (4C-2e Bond): Structure of AlCl3:

(24) What is the difference between the structure of AlCl3 and diborane?

What is the difference between the structure of AlCl3 and diborane?

The hydrogen bridged dimer B2H6 contains two three centre (3C-2e bond), two electron bonds, A three-centre bond uses two electron to link three atoms, and  four two centre, two electron bond (2C-2e). 3C-2e bridge bond is perpendicular to plane in which 2C-2e bond present.

In contrast the bridge bonding in Al₂Cl₆ contains two three centre (3C-4e bond), four electron bonds  which can be described in terms of electron pair bond in which a chlorine atom bonded to one aluminium atom act as a Lewis base by donating a lone pair of electrons to the aluminium atom which acts as a Lewis acid.

Related Questions: 

(1) Why aqueous solution of AlCl3 is acidic in nature ?

(2) What happen when aq AlCl3 react with Acid or Base?

(3) Although anhydrous aluminium chloride is covalent but its aqueous solution is ionic in nature. Why?

(4) Why BF3 do not exist as dimer?. Explain.

(5) Why B-F bond length in BF3 is shorter (130 pm) than B-F bond Iength in BF4- (143 pm)?. Explain.

(6) B-F bond length in BF3 is shorter than B-F bond length in (BF4)- why?

(7) When B2H6 is allowed to react with following Lewis bases, then how may given Lewis base form adduct through symmetrical Cleavage of B2H6.

(8) What is product of reaction between diborane (B2H6) and ammmonia (NH3)?

(9) Why methylation of Diborane (B2H6) replace four hydrogen only ?

(10) What is Use of Boric Acid?

(11) What is use of Orthoboric acids?

(12) What is basicity of "Boric acid" ?

(13) Why Boric acid exist in solid state ?

(14) What is structure of solid Ortho Boric acid ?

(15) What is effect of heat on Borax?

(16) What is the structure of trimetaboric acid and trimetaborate ion?

(17) What is the Sodium per borate ,give the structure and its uses?

(18) Why aqueous solution of borax reacts with two moles of acids ?

(19) What is the molecular formula of Borax ?

(20) Why Boric acid become strong acid in the presence of cis 1,2-diol or 1,3-diol ?

(21) Why Borazine is more reactive than benzene towards Electrophic Aromatic substitution reactions ?

(22) Why Borazine (B3N3H6) is also known as inorganic benzene ?.

(23) Four-center two-electron bond (4C-2e Bond): Structure of AlCl3:

(24) What is the difference between the structure of AlCl3 and diborane?

Chloroform is more acidic than fluoroform why?

We know that acidic strength of the acid also depends upon stability of conjugate bases, so for relative strength of acid, we need to check the relative stabilities of their conjugate bases.

                                                     CF₃^-, CCl₃^-, CBr₃^- CI₃^-

We are expecting the acidic strength haloform acids as CHF₃, CHCl₃, CHBr₃, CHI₃ in decreasing order. Because Fluorine is most electronegative atom so it would be stabilize CF₃^- more, as electronegativity decreases from F to I the stability of conjugate -ve ion would be but that is not correct the actual order is CHCl₃ > CHF₃ > CHBr₃ > CHI₃.

This is because there is effective back bonding in CCl₃- and hence the negative charge partially gets stabilised by back donation to the vacant 3d orbitals of Cl. Thus, CHCl₃ is a stronger acid than CHF₃ and also among them due to 2pπ-3dπ back bonding.

The acidic strengths of the other three haloforms can be compared the inductive effects of their anions. F is very electronegative and hence stabilises the negative charge on the C atom. So, CHF₃ is a better acid than CHBr₃, and the least acidic is CHI₃.

The overall acidic strength order is, CHCl₃ > CHF₃ > CHBr₃ > CHI₃.

Related Questions:

1. How is base strength related to the availabihty of the electron-pair?
2. Amines are more basic than ammonia why?
3. What is relative basic strength order 1° amines , 2°amines and 3° amines ? Explain:
4. Give an explanation for the fact that Guanidine NH=C(CH3)2 is a stronger base than most of amines?
5. Arrange in correct order of basic Character of aniline, pyrrol, pyridine and piperidine?
6. What is correct basicity order of pyridine, pyridazine, pyrimidine and pyrazine ?
7. Give an explanation for the fact that Guanidine NH=C(CH3)2 is a stronger base than most of amines?
8. Arrange in correct order of basic Character of aniline, pyrrol, pyridine and piperidine?
9. What is correct basicity order of pyridine, pyridazine, pyrimidine and pyrazine ?
10. Why pyridine is more basic than Pyrrole?
11. Why pyrimidine is less basic than pyridine?
12. Imidazole is more basic than pyridine? Why?
13. Biological Important of Imidazole and structure:
14. Pyridine is almost 1 million times less basic than piperidine? Why?
15. Cyclohexylamine amine is the stronger base than Aniline? Why?
16. Tetrahydroquinoline amine is the stronger base than Tetrahydroisoquinoline? Why?
17. Arrange the following in the order of increasing basicity : p-Toluidine, N, N-Dimethyl-p-toluidine, p-Nitroaniline, Aniline. (I.I.T.1986)
18. Arrange the following in the increasing order of their acid strength : Methyl amine, Dimethyl amine, Aniline, N-methyl aniline (I.I.T, 1988).