How do covalent bonds form between atoms?
The correct answer and explanation is:
Covalent bonds form when two atoms share one or more pairs of electrons. This sharing allows each atom to achieve a more stable electron configuration, typically resembling that of the nearest noble gas. The process usually occurs between nonmetal atoms, which have similar tendencies to attract electrons.
In more detail, atoms have electrons arranged in shells around their nuclei. The outermost shell, known as the valence shell, determines the atom’s chemical behavior. Atoms tend to become stable by having a full valence shell, which often means having eight electrons, following the octet rule. However, hydrogen is an exception, as it aims for two electrons to fill its valence shell.
When two atoms approach each other, their valence electrons can interact. If the atoms have similar electronegativities, meaning they attract electrons with roughly the same strength, they tend to share electrons equally, forming a nonpolar covalent bond. In this case, the electron pair is shared symmetrically, and the resulting molecule has no partial charges.
If the atoms differ in electronegativity, the shared electrons are pulled more toward the atom with the higher electronegativity. This uneven sharing creates a polar covalent bond, where one atom carries a partial negative charge, and the other carries a partial positive charge. Such polarity affects the physical properties of the molecule, like boiling point and solubility.
Metals generally do not form covalent bonds because they tend to lose electrons and form positive ions instead. However, certain compounds between metals and nonmetals can exhibit some degree of covalent character, especially when the difference in electronegativity is not large.
Overall, covalent bonding is a fundamental chemical interaction that explains the formation of molecules such as oxygen (O₂), water (H₂O), and methane (CH₄). It is essential for the structure and function of countless chemical compounds in both inorganic and organic chemistry.