HF, or Hydrogen Fluoride, is a colorless and odorless chemical compound. Produced by the reaction of hydrogen with very reactive element fluorine, HF can exist as a colorless gas, fuming liquid, or as an aqueous solution, called Hydrofluoric acid. HF can be used to make refrigerants, herbicides, pharmaceuticals, fluorescent bulbs, etc.
So, Is HF Polar or nonpolar? Yes, HF is a polar molecule because of the unequal electronegativity of both atoms resulting in non-uniform distribution of charge across them, and the molecule results in a net dipole moment 1.91 D.
- Essentially, all molecules can be classified as either polar or nonpolar depending on the kind of bonds that are formed between the elements making up the molecule.
- Hydrogen fluoride (HF) is a compound that is primarily polar. This is due to the high electronegativity of the fluorine that pulls the shared electron pair between H and F more towards its side.
- This leads to the development of a partial negative charge on the F atom and a partial positive charge on the H atom, leading to the generation of a dipole and hence polarity.
What are Polar and Non-Polar Molecules?
|Formation of H-bonds||Formation of van der Waal bonds|
|The bond between elements of different electronegativity||The bond between elements of the same electronegativity|
|Asymmetrical molecular geometrical||Symmetrical molecular geometrical|
|The net dipole is present||The net dipole is absent|
|High boiling and melting point||Low boiling and melting point|
|Charge build-up at poles||No charge build-up|
|Example: water, HF, CHF3, etc.||Example: Pentane, CO2etc.|
Determining the Bond Polarity
There are a variety of bonds between the two main extremes- polar and non-polar. Polar molecules are the ones whose center of positive and negative charges do not coincide with each other.
Certain mathematical and diagrammatical analysis can help determine the polarity of a bond on theoretical levels.
Consider the difference between the electronegativity value of the two atoms in the bond.
• If electronegativity difference > 0.4, the bond is considered polar.
• If electronegativity difference < 0.4, the bond is essentially termed as a non-polar bond.
For a molecule to be polar, polar bonds must exist. After confirming the existence of polar bonds, the Lewis structure of the molecule can be used to determine its symmetry and overall polarity.
You can check the reason for the non-polarity of CO2.
Formation of HF (Hydrogen Fluoride)
Under standard conditions, hydrogen and fluorine exist in a diatomic gaseous state, H2, and F2 respectively.By forming an equation, we can see the formation of HF in its anhydrous gaseous form.
H2 + F2 → 2HF
At industrial levels, HF is produced in a liquid acidic form by virtue of the following chemical equation:
CaF2 + H2SO4→ CaSO4 + 2HF
Polarity of HF
HF is made up of two elements- hydrogen and fluoride. Hydrogen is the first chemical element in the periodic table with only one valence electron (valence shell config.: 1s1).
Fluorine on the other hand possesses seven valence electrons (valence shell config.: 2s2 2p5).
The mathematical calculation for electronegativity
To determine the polarity of HF, we need to consider the electronegativity of hydrogen and fluorine.
Electronegativity for atoms that tend to attract electrons towards themselves more strongly is higher. In this case, the electronegativity of fluorine is 3.98 and that of hydrogen is 2.20.
The difference of both electronegativity = |3.98-2.20| = 1.78
This huge difference in the HF bond leads to a fervent polarisation of the bond, which is also evident in the electrostatic potential map.
Now to determine the overall polarity of the molecule, we need to consider the Lewis structure of the HF molecule.
The Lewis Dot Structure
The Lewis structure will help us know the location of electrons around the atoms in the molecule and how the atoms are organized.
From the structure, it is clear that fluorine, being one of the most electronegative elements in the periodic table will try to pull the shared pair of electrons towards itself and not allow equal sharing between H and F.
Due to this, a negative charge develops on the fluorine atom and the hydrogen is left with a positive charge.
This happens so because of the unequal sharing of electrons, due to which hydrogen is a deficit of electrons and develops a corresponding positive charge.
These positive and negative charges lead to the formation of a net dipole on the HF molecule.
below is the geometrical shape of the lewis structure of HF
Polar vs Ionic Bond
However, a question may arise that the bonds with the formation of charges are considered ionic in nature. Then what is the difference here and why this bond is called polar and not ionic?
The answer to this question is simply that for bonds to be categorized as ionic:
- The difference between the electronegativity of the two elements should be greater than 2.0 and in the case of HF, it is 1.78. You can also check out the reason for the polarity of SCN.
- There must be a complete transfer of electrons from one element to another leading to a complete positive charge on the element that gives the electron and negative charge on the one that takes it.
- In the case of HF, there is an unequal sharing of electrons leading to the development of partial positive and negative charges, thus keeping the bond polar but not ionic.
- The formation of ionic bonds is usually between a metal and a non-metal (example: NaCl), but the polar bonds are customarily between two different non-metals.
The dipole moment of HF
- Under ideal circumstances, if the single valence shell electron of hydrogen is shared with the seven valence electrons of fluorine, it will complete the octet for both the elements.
- Nevertheless, due to the high electronegative value of the Fluorine element, there is a strong electron pull from Hydrogen towards fluorine. As a result, the electron cloud thickens near fluorine and the region around hydrogen becomes electron-poor. Yet, fluorine cannot take away the electron completely and render hydrogen electron-less.
- Outturn, hydrogen gains a partial positive charge and fluorine develops a partial negative charge (as shown in the figure). This leads to the formation of the dipole with its head towards fluorine and tail near hydrogen. The numerical value of the dipole moment hence developed is 1.91 debye.
Due to this biased sharing of electron and not a complete transfer from one element to another, the bond between HF can be termed as polar but not ionic.
Conclusively, HF is a polar element owing to the high electronegativity of fluorine, and the difference between electronegativity equal to 1.78.
Properties of HF
• Molecular weight = 20.006 gm/mol.
• IUPAC Name- Fluorane
• Being a polar molecule, HF can easily dissolve in water and the aqueous solution of HF is termed as hydrofluoric acid which is an extremely strong and caustic acid.
• Melting point = -84˚C (polar molecules usually have a high melting point)
• Boiling point = 19.5˚C. The b.p. is low in comparison to water because HF forms only one hydrogen bond per molecule whereas water has two H-bonds per molecule, which means two lone pairs. More the number of lone pairs, the greater is the amount of heat required to achieve the boiling stage.
Applications of HF
The polar compound Hydrogen fluoride is used to manufacture refrigerants, pharmaceuticals, herbicides, stainless steel wire, aluminum metal, certain plastics, electrical components (ex: silicon semiconductor chips), and fluorescent light bulbs.
In laboratories and industries, hydrofluoric acid is applied to the etching of glass and metal. It is also used as an effective catalyst in oil refineries (to produce gasoline) and nuclear reactors.
• As a cleaner and dust remover
Due to its corrosive nature, hydrogen fluoride in its liquid form is used to remove rust from various substances, polish crystals, and remove water and dirt spots.
Hydrogen fluoride is a colorless and odorless substance used in industries and is a diatomic molecule due to which its atoms have an unequal value of their electronegativity that causes unequal dispersion of charge across H-F bond formed.
The fluorine being more electronegative element gains partial negative charge leaving behind partial positive charge on the hydrogen atom.
So, guys, I hope you have got the answer to the question of the polarity of hydrogen fluoride. if you have any queries, feel free to reach out via the comment section. We will reach out to you as soon as possible.