Why SF6 is inert while SF4 is a very reactive molecule that reacts with H2O rapidly and vigorously?

 

The fact that SF₆ does not react with water is not due to thermodynamic stability. Rather, it is because there is no low-energy pathway for the reaction to take place (kinetic stability). Six fluorine atoms surrounding the sulfur atom effectively prevent attack of water molecules and the sulfur atom has no unshared pairs of electrons where other molecules might attack. In SF₄ , not only is there sufficient space for an attacking species (water) to gain access to the sulfur atom, but also the unshared pair is a reactive site. As a result of these structural differences, SF₆ is relatively inert, whereas SF₄ is very reactive.

Related Questions:

(1) What are the hydrolysis products of urea ?

(2) CCl4 can not be hydrolysed but SiCl4 can be. Why?

(3) Why PCl3 hydrolysed while NCl3 can not be hydrolysed?

(4) Why SF6 behave inert towards hydrolysis?

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

(6) Although Sulphur contain vacant d-orbital but SF6 does not under go hydrolysis. Why ?

(7) Arrange the silicon halides into decreasing order of Lewis acids Character? SiF4, SiCl4, SiBr4, SiI4

Why is BCl3 a strongerLewis acid than BF3 ?

The strength of a Lewis acid is a measure of its ability to attract a pair of electrons on a molecule that is behaving as a Lewis base. Fluorine is more electronegative than chlorine, so it appears that three fluorine atoms should withdraw electron density from the boron atom, leaving it more positive.This would also happen to some extent when the peripheral atoms are chlorine, but chlorine is less electronegative than fluorine. On this basis, we would expect BF₃ to be a stronger Lewis acid. However,in the BF₃ molecule, the boron atom uses sp2 hybrid orbitals, which leaves one empty 2p orbital that is perpendicular to the plane of the molecule. The fluorine atoms have filled 2p orbitals that can overlap with the empty 2p orbital on the boron atom to give some double bond character (Back Bond) to the B–F bonds.

 

As a result of the contribution by resonance structures having some double bond character, the boron atom in BF₃ is not as electron deficient as it is in BCl₃. And hence BCl₃ a stronger Lewis acid than BF₃

What are the characteristics features of π-bond ?

(1) π-bond fired by lateral (sidewise) overlapping of atomic orbitals.

(2) lateral overlapping is only partial, so bonds formed are weaker and hence more reactive than sigma bond.

(3) Free rotation about a π- bond is not possible.

(4) π- bond is weaker than sigma bond.

(5) π-bonds are non directional, so do not determine the shape of a molecules.

(5) π- bond take part in resonance.

(6) π- bond formed by pure or anhybrid orbitals.

What is the difference between 2p and 3p orbitals?

Importance difference in between 2p and 3p Orbitals is their energy.

The energy of atomic orbitals depends upon principal as well as azimuthal quantum number, which is  more common known as (n+l) rule .
According to (n+l) rule the atomic orbital has less (n+l)  value also has less energy vice versa.
If the value of (l):is same for two different orbitals then the greater the value of n greater is energy and vice versa.
For 2p => n= 2, l=0,. =>n+l= 2+0=2
For 3p => n= 3, l=0,. =>n+l= 2+0=3
Hence 3p have more energy than 2p orbital

Why are 2p orbitals higher in energy than 2s?

The energy of atomic orbitals depends upon principal as well as azimuthal quantum number, which is  more common known as (n+l) rule .
According to (n+l) rule the atomic orbital has less (n+l)  value also has less energy vice versa.
For 2S => n= 2, l=0,. =>n+l= 2+0=2
For 2p => n= 2, l=2,. =>n+l= 2+1=3
Hence 2p have more energy than 2s orbital