HI is a polar molecule because of the electronegativity difference of Iodine (2.66) and hydrogen (2.2) atom which causes the formation of partial positive and negative charges on both ends of the molecule, as a result, the molecule has a net dipole moment.
Detailed Explanation: Why is HI a Polar Molecule?
Hydrogen Iodide is a heteronuclear diatomic molecule and a member of hydrogen halide. An aqueous solution of hydrogen iodide is commonly known as hydroiodic acid or hydriodic acid which is considered a strong acid. It is found in both aqueous and gas states under standard conditions however they are interconvertible. HI is used as a strong reducing agent in a redox reaction.
Before entering into its polarity, let’s have some ideas about what polar and nonpolar molecules are,Polar Molecules
Those molecules having electronegativity difference between
bonded atoms so that the formation of dipole charges on the molecules are known as
polar molecules. The net dipole moment shouldn’t be zero in case of polar
molecule because of the induction of partial positive and negative charges on
either end of the molecule.
Polar molecules show little ionic characteristics as they
can conduct heat and electricity, can be soluble in water, and have a strong electrostatic force of attraction.
Examples of Polar molecules: Water (H2O), Nitrogen dioxide (NO2), etc.
Nonpolar Molecules
Those molecules having the same electronegativity value for
bonded atoms so that there are not any form of partial positive and negative
charges within the molecule resulting in the net dipole moment become zero are known
as nonpolar molecules. In many cases, there may exist polar bonds within the
molecules but whole molecules are considered as nonpolar due to the symmetrical geometry of molecules which caused dipole charges of molecules to get canceled.
Nonpolar molecules are pure covalent bonds as they only show
covalent nature i.e. bad conductor of heat and electricity, insoluble in polar
solvents, etc.
Examples of Nonpolar molecules: Carbon Dioxide (CO2), Carbon
Tetrachloride (CCl4), Methane (CH4) etc.
Hydrochloric acid (HI) Polar or Nonpolar (Based on characteristics)
HI is a polar molecule and the Iodine atom closest to the negative side as iodine has a higher electronegativity value. The shared pair of
electrons stay closer to the I atom, as a result, induced partial positive
charge on hydrogen atom and negative charge on iodine atom.
These are some of the characteristics of HI which clearly
elaborate why HI is a polar molecule:
Electronegativity Difference
Electronegativity is the tendency of an atom to attract
shared pair of electrons from its binding partner within a molecule. Higher the
electronegativity value, more strength to pull electrons. If the electronegativity difference between two atoms is equal, shared pair of
electrons are centralized but when the difference occurs, atom having higher E.N,
attracts electrons closer to its nucleus.
In HI molecules,
Electronegativity of H atom= 2.2
Electronegativity of I atom= 2.66
Electronegativity difference= 2.66-2.2= 0.46
Here electronegativity difference between hydrogen and Iodine
atom is 0.46 and according to the Pauli scale if the electronegativity
difference between two atoms is between 0.4 to 2.0, the bond is considered as a polar
bond so that the H-I bond is also polar.
Lewis Structure & Molecular Geometry
In the HI molecule, a total of 8 valence electrons take part in molecule formation in which hydrogen has only one valence electron and iodine has seven valence electrons. By mutual sharing of one electron from each atom, the Lewis dot structure completed.
Hydrogen Iodide has a linear geometry (also called terminus) because it is made up of two different atoms with mutual sharing of electrons. In heteronuclear diatomic molecule, induced charges do not oppose each other so their resultant dipole charge is also not canceled.Dipole Moment
Mathematically, the dipole moment is the product of charge and the separation between the atom within the molecule. It is denoted by and given be,
Dipole
moment (µ)= Charge (Q) * distance of separation (r)
It is measured in Debye units denoted by ‘D’. 1 D = 3.33564 × 10-30 C.m, where C is Coulomb and m denotes a meter.
The dipole moment is a vector quantity and depends on the
resultant of the dipole charges i.e. if a molecule has symmetrical geometry,
the net dipole moment will be zero. But HI is a heteronuclear diatomic molecule
so that induced charges do not cancel each other as a result net dipole moment
of the molecule is 0.38 D which makes the molecule polar.
Electron Affinity
Electron affinity is the possibility of finding an
electron inside an atom or a molecule. It is impossible to determine the exact
position of an electron at a particular time but we can estimate the probable
position of an electron according to its behavior and orbit.
Here in the case of HI, Iodine has a higher electronegativity
value so it pulls a shared pair of electrons from the hydrogen atom and that’s why the chances of finding an electron is higher closer to the iodine atom.
Solubility Principle
As we know the solubility principle “like dissolves like”,
HI is mostly soluble in only polar solvents and very rarely soluble in nonpolar
solvents which directly reflects its polarity nature. Further, it is extremely
soluble in water (H2O) which is also a polar solvent.
Clarify your doubts
Sources & Preparation of HI
HI is prepared by reacting Iodine gas (I2) and Hydrazine
(N2H4) for industrial purposes on a large scale which yields hydrogen iodide and
nitrogen gas.
I2 + N2H4 Ã
HI + N2
In general, it can be prepared by the normal reaction of H2 and
I2.
I2 + H2 Ã 2HI
Properties of Hydrogen Iodide (HI)
1. It is a colorless gas, has a molar mass of 127.904 g/mol with melting and boiling point -50.80 °C and -35.36 °C respectively.
2. It is a strong reducing agent and highly soluble in water, gives
a fume of hydroiodic acid when it comes in contact with moist air.
3. It is a toxic and corrosive gas that causes severe hazards to
death when it comes to contact with skin or inhalation. Mainly the vapor of HI
is severely irritating to the mucous membrane of the nose and eyes.
Uses of Hydroiodic acid (HI)
- It is used as a strong reducing agent mostly used for the preparation of acetic acid which is further used at the time of production of vinegar.
- It is highly acidic in nature so it can easily kill many harmful germs and bacteria. This is the main reason it is used as a disinfectant and sanitizer for medical tools.
- It is used in the field of agriculture, forestry, fishing and hunting, mostly as non-pesticidal.
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