Hydrogen Chloride (HCl) is a polar molecule due to the higher electronegativity difference between Hydrogen (2.2) and Chlorine (3.16) atoms. Chlorine has higher E.N than hydrogen so that Cl atom attracts electron from H atom causes the formation of a partial positive charge on chlorine and partial negative charge on hydrogen, as a result, the HCl molecule has a net dipole moment.
Detailed Explanation: Why is HCl a Polar Molecule?
HCl, whose chemical name is hydrogen chloride, is one of the frequently
used acids. The aqueous solution of hydrogen chloride is known as hydrochloric acid which we use most of the time in the laboratory.
Before entering deep inside HCl polarity first, have some
basic ideas about what polar and nonpolar molecules are:
Polar Molecules
Polar molecules are defined as the presence of polar bond
within the molecule or have irregular geometry (not symmetrical structure) so
that the net dipole moment of molecule can’t be zero as the center of gravity
of negative charge and positive charge is separated by a small distance. In the
absence of an electric field, the moment of polar molecules in dielectric substances are randomly oriented but as soon as the electric field is applied, it tends to
align along the direction of the field.
These molecules are used to show little ionic as well as
covalent characteristics i.e. they are soluble in water (H2O), a good conductor of
heat and electricity, have a strong electrostatic force of attraction, and many
mores ionic characteristic despite having covalent bonds i.e. mutual sharing
of electrons.
Example of Polar molecules: Water (H2O), Nitrogen Dioxide
(NO2), Ammonia (NH3) etc.
Nonpolar Molecules
Nonpolar molecules are considered as pure covalent bonded
molecules which are formed by mutual sharing of electrons and have a net dipole
moment zero. In nonpolar molecules, there is no occurrence of partial positive
and negative charge on the atoms because of the same electronegativity different
between the atoms (Diatomic molecules like H2, O2, N2, etc) or molecule has
regular geometry (symmetrical molecules like CH4, CCl4, CO2, etc) so bond
polarities are canceled by each other.
When Nonpolar molecules are placed in an electric field, the
center of gravity of the positive charge moves in direction of the field, and the center of the gravity of the negative charge in opposite direction. This separation between
positive and negative charges continue until the applied external force and
internal force are balanced.
Hydrogen chloride (HCl) Polar or Nonpolar (On the basis of characteristics)
HCl is a polar molecule and the chlorine atom closest to
negative side because of electronegativity of the chlorine atom is higher than
hydrogen so that it pulls shares pair of electrons from H atom as a result
formation of partial positive charge on hydrogen and negative charge on chlorine
atom.
Electronegativity Difference
Electronegativity is the tendency of an atom to attract lone
pair of electrons towards itself from the sharing partner atom. It means atoms
having higher electronegativity value than its bonding atom, the shared pair of
electrons are not centralized i.e. shared electrons in the bond are more or lesser
closer to the atoms having higher E.N value.
Electronegativity difference is a very important factor to
determine the polarity of any molecules either polar or nonpolar. According to
Pauli scale, if the electronegativity difference between two atoms is between 0.5 to
2.0, it is considered as a polar bond between them. In HCl molecule,
Electronegativity of H= 2.2
Electronegativity of Cl= 3.16
Electronegativity difference= 3.16-2.2= 0.96
As mentioned above, if E.N difference between two atoms is
more than 0.4, it is considered as a polar bond and E.N difference between H and
Cl is 0.96 so the bond between them is a polar covalent bond.
Lewis Structure & Molecular Geometry
HCl is a heteronuclear diatomic molecule in which a total of 8
valence electrons are available for Lewis structure i.e. hydrogen has one and
chlorine has 7 valence electrons. Both chlorine and hydrogen share one-one
electrons at the time of H-Cl bond formation.
Dipole Moment
For any molecule being polar or nonpolar, the net dipole
moment is the primary factor. Molecules having net dipole moment zero are known as a nonpolar
molecule and having net dipole moments are considered as a polar molecule.
The net dipole moment is the product of dipole charge and
distance between the atoms. It means the higher the electronegativity difference
between the atoms, the higher the partial charge will be, as a result, the dipole
moment is also higher. HCl has the net dipole moment 1.03 D and the bond length
is 127 pm.
Electron Density
Electron Density is defined as the probability of the shared
pair of electrons to present at a dedicated position within the molecule. But
due to differences in electronegativity, the shared pair of electrons stay closer to
the atom has a higher E.N value. In HCl, electrons are closer to the chlorine
atom due to its higher E.N value. It means the chlorine atom has higher electron
density and the chances of finding electrons are higher closer to the Cl atom in the HCl
molecule.
Solubility Principle
According to the solubility principle “likes dissolve in likes”, means polar molecules dissolve in polar solvents and nonpolar molecules
dissolve in nonpolar solvents. As HCl is a polar molecule, it dissolves in
polar solvents like water.
Clarify your doubts
Sources of Hydrogen Chloride (HCl)
1. Naturally, Hydrogen Chloride is found in our stomach which
helps in the digestion of food i.e. acts as an acidifying agent human body.
2. It can be produced directly by the reaction of chlorine gas
with water. But for laboratory and large industrial purposes, it is mostly
prepared by the reaction of sodium chloride (NaCl) and sulphuric acid (H2SO4).
Properties of HCl
- It is colorless, non-flammable with an acrid odor gas. It is also a poisonous and corrosive hazard gas because it can easily react with most of the metals to form explosive hydrogen gas causes severe pain burns and irritation to the eye and mucous membranes.
- It has a molar mass of 36.46 g/mol with a density of 1.49 g/L and the net dipole moment is 1.05 D.
- It has a higher dissociation constant i.e. H+ ion in the reaction so that it has a strong acidic nature.
Uses of Hydrochloric acid (HCl)
- It is used in the production of batteries, photoflash bulbs, fireworks and many more electronics accessories.
- In daily life, it is used to remove metal stains and leaning stones and tiles because of their corrosive nature.
- It is also used to control the PH of the solution in many pharmaceutical products manufacturing and also used to purify table salts.
Post a Comment