Potassium chloride or KCl is a salt of ionic nature comprising of a metal (potassium) and a non-metal halogen (chlorine). It is, therefore, a metal halide and appears as white or colorless cubic crystals. It does not bear any odor and can easily dissolve in water.
KCl has a density of 1.984 g/cc and a molar mass of 74.55 g/mol. It has a melting point of 7700 C and a boiling point of 14200 C.
We have a redox reaction occurring between KCl and Na to get metal potassium which is then obtained via distillation.
Na + KCL <===> NaCl + K (850 degrees Celcius)
Potassium Chloride has a lot of applications in our day-to-day lives. It is used to treat low blood pressure and therefore has medicinal value.
Also, it is used to manufacture two potash fertilizers: Potassium Chloride and Potassium Sulphate.
Other than this, it is used for soap manufacturing, food processing, anti-freezing agents, welding, soldering as well as a source of beta radiation for calibration purposes.
KCl also has certain safety issues and side effects.
Hence, proper precautions should be taken while handling or dealing with this chemical compound.
KCl Lewis Structure
For understanding the nature of chemical bonding inside any molecule, we need to have an idea about the constituent atoms and the type of bond formation.
Drawing a probable Lewis Structure gives us a clear picture of a 2D molecular composition along with electron dots and bond formation.
Despite its few limitations, the initial step towards deciphering chemical bonding is via Lewis Structure.
Here, we have a KCl molecule formed by one atom of potassium and one atom of chlorine.
Valence electrons refer to the electrons present in the outermost shell of the element which determines the valency of an atom. We can calculate the valence electron number of an element from the periodic table with the help of its atomic number value.
Let us first count the number of valence electrons in the molecule.
Here, we have an image of the modern periodic table.
Potassium belongs to group 1 and has 1 valence electron as per the periodic table. On the other hand, Chlorine belongs to the group of halogens in group 17 and has a valency of 7.
Therefore, the total number of valence electrons in KCl = 1 + 7 = 8.
Now, before we draw the atomic elements and the electrons surrounding them, we must note that KCl is an ionic compound i.e it has an ionic bond and not a covalent bond attaching the two atoms together.
In the case of covalent bond formation as in NO, we found out that two valence electrons are shared to form one bond. In ionic bonds, electrons will be transferred for bond formation.
In this diagram, we can identify the atomic symbols for the constituent elements inside a potassium chloride molecule.
Here, we have attached the valence electrons accordingly. Now, we have the octet rule.
Octet rule: The elements present in group 1 to group 17 i.e the main group elements have a tendency to fulfill their outer shell configuration like the noble gases. For example, Carbon tends to have an octet configuration to have the Neon configuration and Silicon tends to have that of Argon.
So, if we look at our sketch, we can find out that the Chlorine atom is one short of achieving the octet however K has only one valence electron.
For both the elements to have eight valence electrons, Potassium will lose its electron and transfer it to chlorine.
The electronic configuration of K which is 1s2 2s2 2p6 3s2 3p6 4s1 now becomes 1s2 2s2 2p6 3s2 3p6 or [Ar].
And that of Cl which is 1s2 2s2 2p5 now becomes 1s2 2s2 2p6 or [Ne].
Hence, both of them have fulfilled the octet rule.
Now since K lost an electron, it becomes a cation with a +1 positive charge, and Cl, by gaining an electron, becomes an anion with a -1 negative charge.
We have achieved our most suitable Lewis Structure for the molecule: Potassium Chloride.
When we are writing the compound, we do not mention the charges any more:
K+ + Cl- ——-> KCl
Now, we proceed to the next section.
KCl Molecular Geometry
When we talk about covalent compounds, we decipher the molecular geometry from the Lewis Structure with the help of VSEPR theory that deals with lone pairs and bond pairs of electrons.
In ionic compounds, electrons are not shared but transferred resulting in one atom carrying positive charges and another atom carrying negative charges.
Here, to describe the 3D shape, we will discuss the crystal structure of the compound.
Usually, the ionic compounds which have metals and non-metals in the ratio of 1:1 belong to FCC packing.
Therefore, in KCl, we get the FCC arrangement i.e Face Centered Cubic solid just like NaCl or sodium chloride.
Here, a unit cell will comprise four atoms, and the atoms are closely packed occupying 74% of the total volume.
The chlorine anions form the CCP or Cubic Close Packed crystal. The cations of potassium take up the octahedral holes. Both types of ions now can touch each other along the edges of the crystal-packed structure.
Orbital hybridization is a model that refers to the concept of fusion or mixing of atomic orbitals of the same atom inside a molecule having equivalent energies to form hybridized orbitals. Example: one s and three p orbitals come together to form 4 sp3 hybrid orbitals.
We use this model to explain bonding inside covalent compounds to provide a logical explanation.
Since KCl is an ionic compound, we do not need hybridization as we know K carries a +1 and Cl carries a -1 charge via charge transfer.
Polarity is another characteristic or property of a chemical compound. It deals with the separation of electric charges among the atoms inside the molecular composition.
If we want to find out whether a compound is polar or nonpolar in nature, we have to first understand the concept of electronegativity.
Electronegativity is the property of an element that determines or denotes the power or degree to which that particular element can gain electrons i.e. negative charges.
If inside a molecule we have elements having different values of electronegativity and the difference is quite noticeable, which results in charge separation.
The more electropositive atomic element will have a partial positive charge and the other will bear a partial negative charge forming a polar bond.
Now, we have to see how we can know the values of electronegativity of K and Cl.
Here, we have the Pauling electronegativity chart:
As we can see in the table, K has a value of 0.82 and Cl has a value of 3.16.
The difference is around 2.34.
Now, a molecule is considered to be non-polar or pure covalent when the electronegativity difference is less than 0.4 approx. When the value ranges from 0.4 or 0.5 to around 1.8-2, it is called polar covalent.
Here, we have a value of 2.34 and this signifies that the bond is ionic.
With the increase in electronegativity difference, the nature of the bond becomes more ionic. KCl or potassium chloride salt is soluble in polar solvents where it gets dissociated into K+ and Cl- ions.
In this article, we have talked about the bonding nature of KCl or potassium chloride molecule in detail.