American Chemical Society (ACS) Chemistry Test 2025 – 400 Free Practice Questions to Pass the Exam

The formation of a covalent bond occurs when two atoms share a pair of electrons. This typically happens between nonmetal atoms, which have similar electronegativities and thus an affinity for electrons. In a covalent bond, each atom contributes one electron to the shared pair, allowing both to attain a more stable electronic configuration, which often resembles that of the nearest noble gas.

Covalent bonding is illustrated in molecules such as water (H2O) and carbon dioxide (CO2), where the atoms share electrons to fulfill their valence shell requirements. This shared electron pair holds the atoms together, creating a stable molecule with distinct properties.

In contrast, ionic bonds result from the transfer of electrons from one atom to another, leading to the formation of charged ions. Metallic bonds involve a 'sea of electrons' that are delocalized over a lattice of metal cations, allowing for conductivity and malleability. Hydrogen bonds are weaker interactions typically found between polar molecules due to the attraction between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom. Each of these bond types has distinct characteristics and formation mechanisms, but covalent bonds are specifically defined by the mutual sharing of electrons between atoms.