International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

How is a covalent bond formed?

1. By the transfer of electrons from one atom to another

2. By the sharing of a pair of electrons between two nuclei

3. By the magnetic attraction between charged particles

4. By the repulsion of two positive charges

The correct answer is: By the sharing of a pair of electrons between two nuclei

A covalent bond is formed through the sharing of a pair of electrons between two atomic nuclei. This sharing allows each atom to attain a more stable electronic configuration, often resembling that of the nearest noble gas. In a covalent bond, the electrons that are shared contribute to the overall stability of both atoms involved. This mutual attraction not only holds the two atoms together but also facilitates the formation of molecules. For instance, in a simple molecule like hydrogen (H₂), each hydrogen atom shares one electron, resulting in a pair of electrons that orbit both nuclei, effectively holding them together by the attractive force between the positively charged nuclei and the shared electron pair. This behavior is foundational for understanding the nature of covalent compounds and molecular structures, which are characterized by specific shapes and bond angles due to the spatial orientation of these shared electron pairs. The other choices describe different types of interactions. The first option refers to ionic bonding, where electrons are transferred instead of shared, resulting in charged ions. The third option mentions magnetic attraction, which is not relevant for covalent bonding. Finally, repulsion between positive charges does not lead to the formation of bonds; instead, a stable bond arises from the balance of attractive forces in covalent interactions.