Potassium chloride or KCl is a metal halide composed of Potassium (Group 1 metal) and chlorine (Group 17). It is white in color and odorless.
The crystals of KCl are cubic. The taste is similar to the salt used in cooking.
It is found in pure form in nature. We can obtain KCl from various minerals (carnallite, potash, and sylvite), brines, or ocean water.
It is readily soluble in water like sodium chloride. The solubility of potassium chloride in water increases with an increase in temperature.
It is a neutral salt formed by a neutralization reaction between a strong base (KOH) and a strong acid (HCl).
So, is KCl polar or non-polar? KCl is a polar compound. The shape of KCl is linear. There is a difference in electronegativity between K and Cl. Cl is more electronegative than K, and hence the K-Cl bond is polar. Since it is a diatomic compound, polar bond results in a polar molecule.
In this article, we will study the polarity of KCl in more detail. Stay connected.
Why is KCl Polar?
The polarity of a compound depends on the net dipole moment.
A compound is non-polar if the net dipole moment is equal to zero and polar if it is equal to a non-zero value.
The net dipole moment, in turn, depends on various factors. Some of them are-
• Geometry or symmetry
• the difference in electronegativity between constituting elements
• Distance between charges
KCl is a diatomic compound. Diatomic compounds are linear in shape.
There is only one type of bond in the compound between K and Cl.
K is a Group 1 metal. All the elements of this group are electropositive, which means they tend to lose one electron to complete their octet.
Cl is a group 17 halide. All the elements of this group are electronegative, which means they tend to gain one electron to complete their octet.
The electronegativity of K and Cl are 0.82 and 3.16, respectively. The difference is 2.34, which is more than 1.5.
This significant difference indicates that KCl is an ionic compound.
Due to the difference in electronegativity, the dipole moment is developed, directed from partial positive charge (on K) to partial negative charge (on Cl).
Net dipole moment is non-zero for KCl. It is a polar compound.
You must also readout is KCl ionic or covalent.
What is Polarity?
Polarity is one of the essential properties that affect many other compounds’ properties. Generally, two electrons are involved in bond formation.
These shared electrons can either be shared equally or more shifted towards one atom.
The equal sharing of electrons is possible only when the two elements constituting the bond are the same and are present in the same environment.
This equal sharing results in non-polar bonds. For example- O2
Readout about the polarity of O2.
The two elements forming the bond are not the same in most cases. Either of them is more electronegative than the other.
Thus, the more electronegative element attracts the shared pair of electrons towards itself.
This leads to an unsymmetrical distribution of electrons in the bond, and hence positive and negative poles are developed.
The element which attracts the electrons develops a partial negative charge while the other element, which is electron deficient, develops a partial positive charge.
This creation of poles in a bond leads to polar bonds.
A compound with polar bonds can be nonpolar because of symmetry.
Difference Between Polar and Non-polar Compounds
|Basis||Polar compound||Non-polar compound|
|Intermolecular forces||Strong intermolecular forces||Relatively weaker
|Melting and boiling point||Generally higher||Generally, relatively lower|
|Electricity conduction||Conducts electricity in
|It does not conduct
|Electron cloud||Distorted||Not distorted|
|Electronegativity difference||High (>0.4)||Low|
Factors affecting Polarity of a Compound
A compound is considered polar if we can assign a positive and a negative pole. We can determine the polarity of a compound by determining the net dipole moment.
Various factors affect polarity. Some of them are
1. The Dipole Moment of a Bond
It is a vector quantity that means it has a direction along with magnitude.
It is the product of the magnitude of charges and the distance between them. The SI unit is Debye. The formula for the same is
µ (Cm) = Q (C) * r (m)
where µ is dipole moment,
Q is the magnitude of charges, and
r is the separation distance between two charges.
The charges are developed due to the difference in electronegativity of the two elements forming the bond.
2. The Difference in Electronegativities
Electronegativity is the property of an element to attract the shared pair of electrons towards itself.
If both elements forming the bond have the same tendency, then the electrons will not move in either direction and will remain shared equally.
This is the case for homoatomic diatomic molecules. Such bonds are non-polar bonds.
If the two elements have different electronegativity, the shared pair of electrons will be attracted towards the more electronegative element.
The more electronegative element develops a partial negative charge, and the other element develops a partial positive charge.
This leads to the formation of polar bonds.
There is no effect of geometry on diatomic compounds since they are always linear.
If a bond is polar or non-polar, the compound is also polar or nonpolar, respectively, for a diatomic compound.
If a compound has polar bonds, the net dipole moment can be zero or non-zero, depending on the symmetry of the molecule’s shape.
If a molecule is symmetrical and all side atoms are the same, dipole moment vectors can cancel each other out.
For example- SiO2
If the shape is not symmetrical or the side atoms are not the same, dipole moment vectors do not cancel each other out.
For example- H2O, CF2Cl2
I have also written about the geometry of KCl. Check out the article on the lewis structure, geometry of KCl.
4. Distance Between Poles
From the formula of dipole moment, we see that dipole moment is directly proportional to the distance between the poles.
How is KCl Formed?
The electronic configuration of K is 1s2 2s2 2p6 3s2 3p6 4s1.
K can lose the electron in 4s subshell to form K+ cation. This gain will result in completing the octet and attaining a stable configuration.
The electronic configuration of Cl is 1s2 2s2 2p6 3s2 3p5.
Cl can gain one electron in the 3p subshell to form Cl- anion. This loss will result in the completion of the octet and the attainment of a stable configuration.
For the formation of KCl, the electron from 4s of K is donated to 3p of Cl.
In this way, the octet of both atoms is complete, and a bond is formed.
Since the bond is formed between a metal and a non-metal, it is an ionic bond.
The crystal structure of KCl is formed by FCC unit cells.
FCC Crystal of KCl
The crystal of KCl is a rock salt crystal structure. This structure is formed if the anion is larger. Cl- is larger than K+. In KCl, the cation-anion ratio is 1:1.
Anion occupies the lattice sites, and the cation occupies the voids.
The radius ratio (r of K+/r of Cl-) is between 0.414 and 0.732.
This implies that cations occupy octahedral voids.
Thus, each potassium ion is bonded to 6 chloride ions, and each chloride ion is bonded to 6 potassium ions. The coordination number ratio is 6:6.
In FCC, there are 4 ions in total. Out of four, one ion constitutes the 8 corners (1/8 ion on each corner), and three ions constitute the 6 faces (half ion on each face). Thus, there are 4 chlorine ions.
4 chloride atoms in lattice imply 4 potassium ions.
The octahedral voids are present at the 12 edge center (1/4 cation in each void) and at the body center. (1 cation)
Sometimes, crystals of KCl appear violet due to excess potassium ions.
Potassium ions are deposited on the surface of KCl on heating. The chloride ions are diffused to the surface of the crystal, and the potassium atom loses an electron to form K+.
This electron occupies anionic sites called f centers. These f-centers are responsible for color.
• Component of fertilizer
• Preparation of potash
3. Raw material for K metal, KOH, etc.
4. Soap industry
5. Calibration of radiation monitoring equipment which is a source of beta radiation 6. Gas welding of Al
7. Fire extinguisher
8. pH buffer
KCl is a polar ionic compound because of the high difference in electronegativities of K and Cl. The dipole moment vector is directed from K to Cl.