Covalent bonds heteronuclear diatomic molecule

A covalent bond, as we have said, is the sharing of an electron pair by two atoms. In a homomclear diatomic molecule like H2, in which the atoms are identical, the electrons are equally shared, that is, the electrons spend the same amount of time in the vicinity of each atom. However, in a covalently bonded heteronuclear diatomic molecule like HF, the H and F atoms do not share the bonding electrons equally because H and F are different atoms... 

An HC1 molecule is a heteronuclear diatomic molecule composed of H (EN = 2.1) and Cl (EN = 3.0). Because the electronegativities of the elements are different, the pull on the electrons in the covalent bond between them is unequal. Hence HC1 is a polar molecule. 

Let us now consider heteronuclear diatomic molecules. Start with the fact that hydrogen fluoride, HF, is a gas at room temperature. This tells us that it is a covalent compound. We also know that the H—F bond has some degree of polarity because H and F are not identical atoms and therefore do not attract the electrons equally. But how polar will this bond be ... 

In a homonuclear diatomic molecule X2, the electron density in the region between the nuclei is symmetrical each X nucleus has the same effective nuclear charge. On the other hand, the disposition of electron density in the region between the two nuclei of a heteronuclear diatomic molecule X—Y may be asymmetrical. If the effective nuclear charge of Y is greater than that of X, the pair of electrons in the X—Y covalent bond will be drawn towards Y and away from X. 

All these various bonds, whether single or multiple, are called covalent bonds. However, it is possible even in this simple approach to recognize the difference between non-polar covalent bonding and polar covalent bonding. In a homonuclear diatomic molecule, the shared electron pair or pairs must be shared equally and thus there is no polarity in the system nucleus-elec-trons-nucleus. In a heteronuclear diatomic molecule, however, one of the... 

The hydrogen molecule has provided an example of covalent-ionic resonance in a particular bond. Because structures (3-IVb) and (3-IVc) are of importance in an accurate description of the bond from the VB point of view, we say that the bond has some ionic character. However, the polarity that (3-Vb) introduces is exactly balanced by the polarity that (3-Vc) introduces, so that the bond has no net polarity. It is therefore called a nonpolar covalent bond. It is important not to confuse polarity and ionic character, although, unfortunately, the literature contains many instances of such confusion. When we turn to a heteronuclear diatomic molecule, we necessarily have bonds that have both ionic and polar character. Even for the pure covalent canonical structure of HC1 (3-Ia) there is bond polarity... 

Other heteronuclear diatomic molecules polar covalent bonds... 

The characteristic feature of heteronuclear diatomic molecules that will be familiar from introductory chemistry is that the electron distribution is not symmetrical between the atoms because it is energetically favorable for a bonding electron pair to be found closer to one atom rather than the other. This imbalance results in a polar bond, which is a covalent bond in which the electron pair is shared unequally by the two atoms. 

In a molecular compound, covalent bonding happens when two nonmetals share electrons. Covalent bonds are defined not only by the number of electrons shared but also by their length and strength. Covalent bonds have a specific bond length and bond energy. In a homonuclear diatomic molecule where both atoms are identical, the pair or pairs of electrons is/are shared equally between the two atoms. However, in a heteronuclear diatomic molecule, one shared pair(s) will be more attracted to one atom than the other. 

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