4.3. Chemical Bonds: Covalent bond

The chemical bond is the process that joins two or more atoms to form molecules. This union occurs due to the exchange or sharing of electrons between atoms. In this chapter of our course, we are going to cover one of the most common types of chemical bonding: the covalent bond.

A covalent bond occurs when two atoms share one or more pairs of electrons in their valence shells. This happens because atoms seek to reach a state of greater stability, which is normally reached when the valence shell is full. In the case of atoms that form covalent bonds, they share electrons so that both can reach this state of stability.

For example, consider the water molecule (H2O). It is made up of two hydrogen atoms and one oxygen atom. Each hydrogen atom has one electron in its valence shell, while oxygen has six. To reach a state of greater stability, hydrogen atoms share their electrons with oxygen, forming a covalent bond.

Covalent bonding can be classified into two types: polar covalent bond and nonpolar covalent bond.

In polar covalent bond, shared electrons are more strongly attracted to one of the atoms. This occurs when the atoms involved in the bond have different electronegativities. Electronegativity is a measure of an atom's ability to attract electrons. In water, for example, oxygen is more electronegative than hydrogen, so the shared electrons are more attracted to oxygen, making the bond polar.

On the other hand, in nonpolar covalent bond, shared electrons are equally attracted to both atoms. This occurs when the atoms involved in the bond have the same or very similar electronegativities. An example of a molecule with a nonpolar covalent bond is nitrogen gas (N2), where the two nitrogen atoms share electrons equally.

It is important to note that the polarity of a molecule does not depend only on the polarity of its bonds, but also on its geometry. Molecules with symmetrical geometry can be nonpolar, even if their bonds are polar, because the symmetry causes the polarities of the bonds to cancel.

Understanding covalent bonding is critical to understanding the structure and properties of molecules. This understanding is essential for many areas of chemistry, including organic chemistry, medicinal chemistry, and biochemistry. Also, questions about covalent bonds frequently appear on exams like the Enem, so it's a topic worth mastering.

I hope this chapter has helped you better understand covalent bonding. In the next chapter, we'll explore another type of chemical bond: the ionic bond. Stay tuned!

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