Covalent bonds: what are they?

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Covalent bonds form between atoms with similar electronegativity, creating molecular orbitals where electrons roam freely. They are the strongest type of bond, but not common in life processes due to their difficulty to break. Other types of bonds include ionic, hydrogen, and van der Waals forces.

Covalent bonds are the strongest type of chemical bond and are created between atoms with similar electronegativity. In general, electronegativity increases towards the right of the periodic table and decreases down the table. Electronegativity is not an atomic property, but arises when atoms interact with each other.
According to modern atomic theory, atoms have electrons surrounding them in shells called orbitals. Each orbital has a maximum number of electrons and each atom “wants” to maximize its electrons in each orbital. The noble gases are the most stable elements because their electron orbitals all carry the maximum number of electrons. They are unable to form covalent bonds.

When two or more atoms have similar electronegativity, the conditions are ripe for covalent bonding. The electron orbitals of both atoms seek out similar numbers of other electrons to maximize their electron shells. When atoms are brought together, their electron shells mix and create something called “molecular orbitals,” in which electrons roam freely between both atoms and orbit the nuclei of both. This makes covalently bonded materials, such as diamond and many metals, quite conductive. In contrast, with ionic bonds, such as the type of bonds that hold sodium chloride (salt) together, the electrons remain in their respective atoms and as a result the overall molecular structure is weaker.

Covalent bonds are not common within life processes because it takes too much energy to break them, making them too difficult to work with. Depending on the number of shared electron pairs, the bond is characterized as single, double, triple, and so on. Some of the metals with the highest melting points, molybdenum and rhenium, have quadruple bonds. Quintuple and sextuple bonds are quite rare, and there is good reason to believe that nothing in the periodic table can go beyond a sextuple bond.

As stated earlier, covalent is the strongest possible type of chemical bond. Other chemical bonds include ionic bonds, hydrogen bonds and the van der Waals force. There are many other types of rare and exotic bonds, but these four are by far the most common.




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