How can we tell if a molecule is formed by an ionic bond?

• A. The atoms share pairs of electrons.
• B. The atoms lose or gain electrons.
• C. The atoms are both nonmetals.
• D. The atoms are identical.

Answer: (B)

Ionic bonding is defined by electrons being transferred from one atom to another, producing ions that are held together by the strong attraction between opposite charges. When electrons are donated by a metal and accepted by a nonmetal, the metal becomes a positive ion and the nonmetal becomes a negative ion, and those ions stick together because they attract each other. This transfer, not sharing of electrons, is what sets ionic bonds apart from covalent bonds. So the best way to tell if a bond is ionic is to look for evidence of electron transfer between atoms. In contrast, bonds formed by sharing electrons (covalent bonds) involve pairs of electrons rather than full transfer, and the other clues—such as both atoms being nonmetals or the atoms being identical—don’t by themselves distinguish ionic from covalent bonding.