Is KCl Ionic or Covalent?

With a molecular weight of 74.55 g/mol, KCl is a metal halide salt. It’s a tasteless, odourless, whitish or colourless crystalline substance with a saline flavour. Elongated, prismatic, and cubic crystals are all possible. It has a refractive index of 1.48 and may be dissolved in water and other polar solvents.

Although this binary salt has a melting point of 771°C, it does not have a boiling point because it sublimes at 1500°C. It can be found in brines and ocean water in nature, as well as in minerals in association with other elements such as sylvinite, carnallite, kainite, potash, and so on.

In this blog, we’ll look at whether KCl is ionic or covalent, as well as the causes for both.

Is KCl an ionic or a covalent salt? Yes, KCl is ionic in nature because potassium has an electronegativity of 0.82 and chlorine has an electronegativity of 3.16, resulting in a difference of 2.34 electronegativity between these two elements, which is larger than 2.0, which is required for the creation of an ionic bond. Furthermore, because ionic bonds are always formed between a metal and a non-metal, KCl can be classified as an ionic compound.

Why is KCl an ionic salt?

To comprehend this, we must first respond to the question, “Why do elements form chemical bonds?”

‘Stability,’ is the straightforward solution to this query.

Every atom wants to keep the electrons in its outer shell stable, thus it engages in chemical bonding to help its valence electrons stay as stable as possible.

In the absence of any other element to stabilise the outer shell, the initial shell is stabilised by two electrons. This applies to hydrogen atoms that link amongst themselves.

Similarly, the octet rule for predicting the stability of other atoms applies after hydrogen and helium atoms (first row elements).

Potassium (K) belongs to the first group and fourth period of the Periodic table, indicating that it has one unstable electron in its outer shell, whereas Chlorine (Cl) belongs to the seventeenth group and third period, indicating that it has seven valence electrons.

As a result, Potassium, which has one more proton than electrons, has a tendency to give up its additional electron, generating K+, and therefore easily lends its lone valence electron to Chlorine, which is one electron shy of forming an octet and is more inclined to take the electron, forming Cl-.

As a result, because potassium and chlorine are oppositely charged ions, they attract each other and form a chemical bond due to the substantial electronegativity difference, resulting in the production of KCl by ionic contact.

This can also be seen in the Lewis structure of KCl (Figure 1), where one of Potassium’s valence electrons is snatched away by Chlorine, which has seven valence electrons in its outer shell, resulting in a stable ionic unit consisting of K+ and Cl-.

Potassium Chloride: Earth’s Chloride Salt—and Mars’, Too?

What are the differences between ionic and covalent compounds?

To fully comprehend the concepts of ionicity and covalence, we must delve deeper into how these two states are achieved.

Ionic compounds are defined as compounds that include at least two oppositely charged ions, i.e. one positive and one negative.

Such connections are most commonly found between metals and non-metals. Ionic compounds are electrically neutral because the charges on the atoms are equal and opposite, resulting in nullification.

The electronegativity difference between the two atoms forming the bond, for example, NaCl, Na2SO4, NH4SCN, etc., is the most significant prerequisite for the creation of an ionic bond (as per some books, more than 1.7).

Unlike ionic compounds, where the connection is created by the transfer of an electron from one atom to another, covalent bonds are formed when certain atoms are unable to give or take an electron and must share one or more of their valence electrons to keep their outer shells stable.

The electronegativity gap between two or more non-metals must be less than 2.0 for such bonds to form.

Furthermore, there are two types of covalent bonds: polar covalent bonds, in which the electronegativity difference is between 2.0-0.5, indicating that the attraction of the more electronegative atom is insufficient to pull the electron entirely towards itself, and thus a partial positive charge appears on one atom while the other atom has a partial negative charge (indicated by the Greek letter delta “). An example of such a bond is HCl.

The electronegativity difference between two atoms in a non-polar covalent connection is less than 0.5, indicating that the electrons are shared approximately evenly between the two atoms. O2, N2, CO2, and other gases are examples.

You may read more about CO2 polarity in this article.

The electronegativity difference between two atoms must be zero for a pure covalent connection to occur, which is impossible.

Similarly, in order to form a wholly ionic link, the atom must give up all of its electrons, which is impossible. As a result, every covalent bond is somewhat ionic and vice versa.

Electronegativity

Electronegativity is a term that describes how strongly an atom attracts the electrons in a chemical connection.

The higher difference in electronegativity between two atoms suggests that one is more likely to take electrons while the other is more likely to lose them.

The Pauling Scale is used to calculate it.

Fluorine is the most electronegative of all the elements, with a value of 4, while cesium and francium are the least electronegative, with a value of 0.7 on the Pauling scale.

In the periodic table, electronegativity decreases from top to bottom in a column and from right to left in a row.

However, the overall trend of electronegativity in the table is diagonal, increasing from the lower-left to the upper-right corner.

Other information about KCl

Fertilizers are the most common application for potassium chloride; more than 90% of KCl generated in the United States is utilised as fertiliser.

Potassium deficiency has a negative impact on plant growth, making it one of the important components required for plant growth. It is supplied under the name ‘Muriate of Potash,’ which is also its historical name.

KCl has antihypertensive properties and is used to treat hypotension by giving it to the patient orally or intravenously to raise their blood pressure.

It’s also used to avoid hypokalemia as a nutritional supplement. Potassium chloride is occasionally used as a substitute for ordinary salt, such as Sodium Chloride, or blended with it to make reduced sodium salts.

Apart from it, Potassium chloride is also used to make soap, is mixed with animal diets to boost milk production in dairy animals, is used as a completion fluid in petroleum and natural gas operations, and is utilised in the glass industry, among other things.

It’s also used as a calibration standard in laboratories to measure the electrical conductivity of solutions.

Conclusion

To summaries, potassium chloride is an ionic compound created by the transfer of one electron from a metal, potassium, generating K+, and acceptance of the same electron by a non-metal, chlorine, forming Cl-, resulting in the formation of a stable ionic unit.

Read more: Molecular Geometry, Hybridization, and Polarity of CH2O2 Lewis Structure

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.

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