Final answer:
Electrons are shared between two atoms in substances with covalent bonds, such as in a diatomic chlorine molecule (Cl2).
Step-by-step explanation:
The sharing of electrons between two atoms occurs in substances with covalent bonds. While ionic bonds involve the transfer of electrons, as in the case of sodium chloride (NaCl), where Na donates an electron to Cl, resulting in the formation of Na+ and Cl- ions, covalent bonding involves the sharing of electron pairs. An example of a covalent bond is when two chlorine atoms (Cl2) share electrons equally, forming a diatomic molecule. However, covalent bonds can also have polar character if electrons are shared unequally between different types of atoms.