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How does covalent bonding hold atoms together in molecular compounds?

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Two diagrams show the three-dimensional structure of a methane molecule: panel A uses a ball-and-stick model with a central carbon atom connected to four hydrogen atoms in a tetrahedral arrangement, while panel B illustrates the bond angle of 109.5 degrees and bond length of 1.09 angstroms between carbon and hydrogen atoms. — chemical compound Methane, in which four hydrogen atoms are bound to a single carbon atom, is an example of a basic chemical compound. The structures of chemical compounds are influenced by complex factors, such as bond angles and bond length.

In molecular compounds, atoms are held together by covalent bonds, which are formed when atoms share pairs of valence electrons. This process typically occurs between nonmetal elements that lack the low ionization energy required for electron transfer.1234

The Mechanism of Bonding

The formation of a covalent bond is energetically favorable because the bonded atoms achieve a lower total energy state than they would as separate, isolated atoms. In the simplest model, known as the valence-bond theory, the shared electron pair is assumed to reside between the two nuclei, where it is attracted to both positive centers simultaneously.53

This sharing is governed by the Pauli exclusion principle, which dictates that an orbital can hold a maximum of two electrons, provided their spins are paired. By sharing these electrons, atoms often attain a stable, closed-shell electron configuration, such as an octet, which further contributes to the stability of the molecule.65

More advanced molecular-orbital theory describes these electrons as being distributed throughout a "bonding molecular orbital" that encompasses both atoms, rather than being strictly localized between them.3