Why SF6 is inert where as SF4 is highly reactive towards H20 ?.

The maximum coordination number of sulphur is 6. Hence S cannot accommodate more than 12 electrons around it. SF₆ is covalently saturated compound. Thus six fluorine atoms around sulphur protect sulphur from attack by reagent to such an extent that even thermodynamically favorable reaction like hydrolysis (S-O bond is stronger than S-F bond) does not occur. On the other hand, in SF₄, the coordination number is only four. Hence sulphur can be attacked by H₂O.

Related Questions:

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

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

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

Question (4): Arrange in increasing order of extent of hydrolysis [ CCI₄, MgCI₂, AICI₃, PCl₅, SiCI₄].

Question (5): Although Sulphur contain vacant d-orbital but SF6 does not undergo hydrolysis. Why?

Question (6): CCl₄ can not be hydrolysed but SiCl4 can be. Why?

Question (7): What are the hydrolysis products of urea?

Question (8): Why SF₆ is inert where as SF₄ is highly reactive towards H₂0?.

Question (9): Why SF₆ behaves inert towards hydrolysis?

Question (10): Why PCl₃ hydrolysed while NCl₃ can not be hydrolysed?

Question (11): Why hydrolysis of NCl3 gives NH4OH and HOCl, while PCl3 on hydrolysis gives H3PO3 and HCl?

Question (12) NCl3 and PCl3 on hydrolysis give different kinds of products. These is because of

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

BF₃ has a planar trigonal geometry due to sp2 hybridisation of boron in BF₃. Boron atom in BF3 is electron defficient (incomplete octet) and fluorine atom is electron rich (due to the presence of three lone pair of electrons on fluorine atom).

Boron and fluorine both belong to the same period. Hence their bonding orbitals have almost same size  and same energies.Thus Back Bonding takes place between B and F. This introduces a partial double bond  character between B-F of BF3. Thus B-F bond length decreases from normal B-F bond length.

 In BF₄^-,the  hybridization of boron is sp3. The B-F bond has pure single bond character. Thus B-F bond length in BF₄^-, is more than the B-F bond length in BF₃ .

 Related Questions: 

Why aqueous solution of AlCl3 is acidic in nature ?

What happen when aq AlCl3 react with Acid or Base?

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

Why BF3 do not exist as dimer?. Explain.

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

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

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

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

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

What is Use of Boric Acid?

What is use of Orthoboric acids?

What is basicity of "Boric acid" ?

Why Boric acid exist in solid state ?

What is structure of solid Ortho Boric acid ?

What is effect of heat on Borax?

What is the structure of trimetaboric acid and trimetaborate ion?

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

Why aqueous solution of borax reacts with two moles of acids ?

What is the molecular formula of Borax ?

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

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

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

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

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