Molecular Orbital Electronic Configurations of Homonuclear Diatomic Molecules

Introduction 

Molecules formed from two atoms per molecule are known as diatomic molecules. The molecules thus formed are attracted to each other with the help of covalent chemical bonds. Remember, the atoms combined can be with the help of a single bond, double bond, and triple bond. Depending on the types of atoms used during the formation of molecules, the diatomic molecules are divided into two main types – homonuclear and heteronuclear diatomic molecules. Though both the molecules are formed with the help of two atoms yet, they are quite different from each other. Read out the article to know more about homonuclear diatomic molecules and the molecular orbital treatment. 

Homonuclear diatomic molecules 

Also known as mononuclear molecules, these molecules are formed from the combination of two substances with the same chemical properties. These two elements are known to bond each other with the help of covalent chemical bonds. For this reason, homo diatomic molecules have two same atoms present in them. Some of the atoms known to have homonuclear diatomic bonding are oxygen, hydrogen, halogen, and nitrogen. 

Remember, noble or inert gasses don’t form diatomic molecules. The homonuclear diatomic molecules are known as nonpolar molecules because of the zero electronegativity difference between them. The two atoms that form chemical bonds are the same, which means both have the same electronegativity. The electron pairs are equally distributed, meaning there is no shift. Hence, the homonuclear molecules are nonpolar. 

However, the bond present between them can be single, double, or triple, as per the demand of the atoms and the valence electrons. Let’s check out the examples of homonuclear diatomic molecules with single, double, and triple bonds present in them. 

1.     Nitrogen molecule (N2), having triple bond present between two nitrogen atoms
2.     Oxygen molecule (O2), having a double bond present between two oxygen atoms
3.     Hydrogen molecule (H2), having a single bond present between two hydrogen atoms. 

Heteronuclear diatomic molecules 

Unlike homonuclear diatomic molecules, heteronuclear diatomic molecules are composed of two different types of atoms. They are known to club different atoms with the help of covalent chemical bonds. Meaning the chemical properties of the two atoms used in the molecule formation are different. Some of the examples of heteronuclear diatomic molecules are Carbon monoxide, Nitrogen oxide, Hydrogen fluoride, and much more. 

Remember, the bond present in the heteronuclear diatomic molecules is always polar. The reason is the electronegativity difference prevailing between the two attached atoms. When two different atoms with different chemical bonds are attached, one of the atoms present in it has a high electronegativity value as compared to the other. This results in the shifting of the electronic pair towards the more electronegative element. Thus, giving rise to the polar nature of the molecule.

Similar to homonuclear diatomic molecules, heteronuclear diatomic molecules can have single, triple, and double bonds present between the two at attached. Here are examples of heteronuclear diatomic molecules with their bonding criteria. 

1.   Carbon monoxide (CO) has a triple bond present between two different atoms – carbon and oxygen. Oxygen being more electronegative will attract the electron pair towards itself, indicating the polar nature of the molecule. 
2.     Nitrogen oxide (NO) has a double bond present between two different atoms – nitrogen and oxygen. Oxygen being more electronegative will attract the electron pair towards itself. 
3.     Hydrogen fluoride (HF) has a single bond present between two different atoms – hydrogen and fluorine. Fluorine being more electronegative will attract the electron pair towards itself, establishing a polar bond between the atoms. 

What are the similarities between homonuclear and heteronuclear diatomic molecules? 

Though both molecules have different bonding criteria yet, there are certain similarities. Check out a few similar qualities that both homonuclear and heteronuclear diatomic molecules possess. 

1. When the atoms are bonded with each other, they both utilise two atoms per bonding. 
2. The geometry of both heteronuclear and homonuclear diatomic molecules is linear. 
3. Covalent chemical bond is present between both homonuclear and heteronuclear diatomic molecules.

    

Key differences between homonuclear and heteronuclear diatomic molecules 

Now that you’ve got an idea of the similarities let’s discuss the differences between the two types of diatomic molecules. These are – 

1. During homonuclear diatomic molecule bonding, the two atoms have chemical properties. On the other hand, during heteronuclear diatomic molecules, the two atoms have different chemical properties. However, in both cases, the chemical bond is covalent. 
2. Homonuclear diatomic molecules have stable isotopes that don’t undergo any radioactive decay. Alternatively, heteronuclear diatomic molecules come with different chemical elements and don’t form stable isotopes. 
3. Homonuclear diatomic molecules possess nonpolar chemical bonding. On the other hand, heteronuclear diatomic molecules possess polar bonds. 
4. Homonuclear diatomic molecules have identical atoms. Heteronuclear diatomic molecules have different atoms bonded. 

MO treatment of homonuclear diatomic molecules

A molecular orbital is a way to determine the filling of electrons in a particular bond formation. Let’s explain the MO treatment of homonuclear diatomic molecules by taking the example of hydrogen molecule (H2). 

Hydrogen Molecule (H2) – When two hydrogen atoms are combined, it results in the formation of a hydrogen molecule (H2). As we know, each hydrogen atom has one electron in its valence shell, that is, one s-orbital. Thus, two atoms of hydrogen will have two electrons present in their shell. The electrons present are fixed in the molecular orbital that has lower energy in it. While pairing the electrons, each of the electron bonds should have opposite spins according to the Pauli exclusion principle. With the help of molecular theory, the bond length, bond dissociation energy, and bond order can be easily calculated. It is diamagnetic due to the unavailability of unpaired electrons. Similar to the hydrogen molecule, we can calculate the same aspects in other homonuclear diatomic molecules with the help of molecular orbital theory. 

Conclusion

Even though homonuclear and heteronuclear diatomic molecules are the types of the same diatomic molecules, they come with large differences. Molecular orbital theory can explain the facts regarding the electron bonding in diatomic molecules. One thing to remember in both types of bonding is that they have differences in atoms that participate in the bonding. We hope this article will help you get a complete insight into homonuclear diatomic molecules and their molecular orbital theory.