HF (Hydrogen Fluoride) is a polar molecule due to the large electronegativity difference between Fluorine (3.98) and Hydrogen (2.2) which leads to induced positive charge on H atom and negative charge on F atom and therefore molecule has the net dipole moment.
Detailed Explanation: Why is HF a Polar Molecule?
Hydrogen fluoride is the chemical name of HF and its aqueous solution is known as hydrofluoric acid. It is a colorless compound at a gaseous and liquid state with an irritating odor. It is normally stored inside the steel cylinder because of its corrosive behavior.
Before entering into its polarity i.e. whether it is a polar or nonpolar molecule, let’s have basic ideas of what polar and nonpolar molecules are,
Polar Molecules
Polar molecules are those molecules having polar bonds within the molecule and have irregular geometry (Not linear or symmetrical) so that the dipole charges (partial positive and negative) on the molecule doesn’t cancel out. For a molecule to be polar, there must be some net dipole moment and this can’t be zero otherwise the molecule becomes nonpolar.
Molecules having polar covalent bonds show both ionic and covalent characteristics. They can easily be soluble in water, can conduct electricity and many more ionic behaviors.
Examples of Polar molecules: Water (H2O), Ammonia (NH3), Nitrogen Dioxide (NO2), etc.
Nonpolar Molecules
Polar molecules are those molecules that have a net dipole moment zero i.e. electronegativity of the atoms in a molecule must be the same or have regular geometry (symmetrical or linear). Nonpolar molecules are considered as pure covalent bonds because they only show covalent nature unlike nonpolar molecules which also show little ionic behavior.
Nonpolar molecules are not soluble in water or any other polar solvents. These are only soluble in nonpolar solvents and also they are bad conductors of heat and electricity as they don’t have free ions.
Examples of Nonpolar molecules: Carbon Dioxide (CO2), Methane (CH4), homonuclear diatomic molecules, Carbon tetrachloride (CCl4), etc.
Hydrogen Fluoride (HF) Polar or Nonpolar (Based on characteristics)
Hydrogen fluoride (HF) is a polar molecule and the Fluorine atom is closest to the negative side as the electronegativity of F atom is higher than H atom so that fluorine pulls the electron from hydrogen at the time of bond formation as results of negative charge induced on fluorine and positive on hydrogen.
These are some of the hydrogen fluoride polarity related characteristics that show why HF is a polar molecule in detail:
Electronegativity Difference
Electronegativity is the tendency of an atom to attract a shared pair of electrons from its binding partner. An atom having a higher EN value exerts more force than an atom having a lower EN value which causes the higher EN value atom pulls shared electrons closer to it, as a result, partial positive and negative charges are induced on the atom within the molecule.
In HF molecule,
Electronegativity of Hydrogen= 2.2
Electronegativity of Fluorine= 3.98
Electronegativity difference= 1.78
From the above data, we can see the electronegativity difference between H and F atoms is 1.78 and according to the Pauli scale, if the electronegativity difference between two atoms is between 0.5 to 2.0, it is considered a polar molecule. 1.7 is the point where molecules show 50% ionic and 50% covalent characteristics. So, it is clearly showing HF is a strong polar compound and has more ionic characteristics.
Also Read: Is XeF2 Polar or Nonpolar? and, Is XeF4 Polar or Nonpolar?
Lewis Structure & Molecular Geometry
A total of 8 valence electrons take parts in the Lewis dot structure of the HF molecule (one from hydrogen and 7 from fluorine). Both H and F atoms share one-one electrons to fulfill its outermost shell and the fluorine atom has 3 lone pair of electrons which do not participate in bond formation.
Dipole Moment
The dipole moment is a major asset for any compound being polar or nonpolar. Those molecules having net dipole moment zero are considered as nonpolar molecules and the rest are polar. Dipole moment can be defined as the products of induced charge and distance of separation. It is denoted by and given by,
Dipole moment = Charge (Q) * distance of separation (r)
It is measure in Debye units denoted by ‘D’. 1D = 3.33564*10-30 C.m, where C is Coulomb and m denotes a meter.
Hydrogen Fluoride has a higher dipole moment of 1.91 D. This is because of the higher electronegativity difference between hydrogen and fluorine as induced dipole charges are higher compared to another hydrogen halide.
Electron Affinity
Electron affinity is an estimated prediction of an electron in the orbital of a molecule or atom. You just determine the exact location of an electron inside a molecule or atom at a particular time but you can assume the maximum possibility of finding an electron in the orbital. In HF, the chances of finding an electron are higher closer to the fluorine atom as it attracts a bonding pair of electrons closer to its nucleus.
Solubility Principle
According to the solubility principle of “Like dissolves like” which means compounds are only soluble in similar types of solvents from which they belong to. Hydrogen fluoride can easily be soluble in water and other polar solvents which further elaborate its polarity nature as it is a polar molecule.
Sources and Preparation of Hydrogen Fluoride (HF)
Normally, gaseous hydrogen fluoride is prepared by the reaction of dried fluorine and hydrogen gas.
When the pure and dried powder of fluorspar (CaF2) is placed with 96% concentrated sulfuric acid, aqueous sulfuric acid is formed.
CaF2 + conc. H2SO4 → CaSO4 + 2HF
Anhydrous Hydrogen Fluoride is obtained when the pure and dried Fremy’s salt (KHF2) is heated at 573K temperature in a copper retort.
KHF2 → KF + HF
Properties of HF (Hydrofluoric acid)
1. Hydrogen fluoride is a colorless gas or liquid (below 19.5 C), has a molar mass of 20.006 g./mol and density of 1.15 g/L, and its melting point is -83.6 °C and boiling point is 19.5 °C.
2. When hydrogen fluoride comes in contact with moisture or water it converts into hydrochloric acid as a result when it comes to contact with skin or other parts of the body, it damages the tissue due to its corrosiveness.
3. Hydrogen fluoride has an anomalous behavior of high melting and boiling points when compared with HCl, HBr, and HI because of the intermolecular hydrogen bonding.
Uses of HF (Hydrogen Fluoride)
- Used in the preparation of many pharmaceutical compounds and different polymers. For example polymers like polytetrafluoroethylene which is commonly known as Teflon.
- Almost 60-70% of hydrogen fluoride is used in the manufacturing of different components of refrigerants which are widely used all over the world in the refrigerator, freezer, and air conditioner.
- It is used for cleaning and purifying different automotive gears, instruments, and many other things because of its high corrosive behavior.
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