Question

write the electrons structure. and atomic structure of Nacl.Hcl. Ch4.Mgcl2

Answer 1

Why is hydrogen chloride (HCl) a covalent compound? Why can't it be an ionic compound?

Answer

21

Follow

Request

More

Ad by Jigsaw Academy

 

Accelerate your career with India's premier analytics institute.

Stand out from the crowd and become job-ready with our exclusive PGDPM program in Bengaluru.

Learn More

14 ANSWERS



Pratik Sarkar

Answered Mar 30, 2016

Hi,

Cl is a Halogen like F. HF is an ionic compound but HCl is a covalent compound.

Now bonds are formed when two atoms share their electron density. Covalent bonds are formed when the participating atoms share half of their combined electron density. So the true covalent bond forms only in homo-nuclear atoms like Cl-Cl or H-H.

The purity of covalency (i.e. the equal sharing of electron density) is diminished when the molecule is hetero-nuclear. If one atom is more electronegative than the other, the atom attracts the pair towards itself thus violating the 'covalency' of the bond. Now the 'covalent' bond is now polar covalent bond. So more the polarity of the bond, more ionic it is and less covalent.

So the bottom line is whether a bond covalent (i.e. combined electron density is evenly shared) or not, depends on the difference between their respective electronegativity.

In case of HCl, the following points should be discussed:

Measurement of partial charge on an atom (measured in coulombs):

Q = u/d

where u is the dipole moment of a molecule ( in debye) and d is distance between the two atoms (in m).

For HCl is value of u is 1.05 debye and

the distance between H and Cl is 127.4 pm which is 127.4 x 10^(-12) m.

1 debye =  3.3356 × 10^(−30) C·m.

So the value of Q is

[1.05 x {3.3356 × 10^(−30)}] / 127.4 x 10^(-12) = 0.027  x 10^(-18) C.

Now as one electron contributes 1.6022 × 10^(−19) C,

the ratio of is 0.027  x 10^(-18) C / 1.6022 × 10^(−19) C = 0.017 x 10 = 0.17  = 17%.

It is estimated that roughly 17% of an electron cloud has been transferred from the hydrogen atom to the Cl atom, making the bond polar covalent but not extreme polar covalent (or ionic) like HF where almost (if you calculate) 41% electron density is transferred from hydrogen to fluorine.

P.S In this sense, the 'purest' covalent heteronuclear compound is PH3 (i.e. the P-H bond) and 'least' covalent (i.e. the 'purest' ionic) compound is CsF.