3: Structure and Properties of Ionic Bonds
Crystal structure of ionic bonds
Remember, the oppositely charged ions in an ionic bond are held together by electrostatic forces. Even more, the charged ions arrange themselves in an alternating fashion to form a solid crystal structure.
Example: Table salt
An ionic compound we frequently encounter in everyday life is sodium chloride (NaCl). We usually call it table salt (fig. 1). It is also the salt most responsible for the salinity of seawater.
Figure 1: Sodium chloride (NaCl) is table salt [CC0 Public Domain]
In NaCl each sodium cation (Na+) is attracted equally to all its neighboring chloride anions (Cl-) and vice versa resulting in a tightly bound crystalline lattice structure (fig. 2).
Figure 2: Schematic model of Na+ and Cl- ions forming a crystal structure. The purple spheres represent Na+ cations, and the green spheres represent Cl− anions. [this picture is public domain]
Properties of ionic bonds
Ionic compounds share many features in common:
They tend to form crystalline structures.
The concept of a single molecule does not apply to ionic compounds since crystalline structures exist as one continuous system.
Ionic compounds have high melting (and boiling) temperatures and are therefore usually in solid phase at room temperatures. This is due to the many simultaneous attractions between positively charged cations and negatively charged anions, which cause ionic crystal lattices to be very strong.
Many ionic compounds dissolve easily in water (and other polar solvents). You will learn more about this in the example of the unit on covalent bonds.
In solution, ionic compounds readily conduct electricity. More specifically: When an ionic compound is dissolved in a solution, the crystal lattice is broken apart and the individual ions can move. These electrically charged ions can flow through the solution and conduct electricity.
- D.W. Ball et al., 2016. The Basics of General, Organic, and Biological Chemistry, ch. 3.3: Formulas for Ionic Compounds. Libre Texts/UC Davis. http://chem.libretexts.org/Textbook_Maps/Introductory_Chemistry_Textbook_Maps/Map%3A_The_Basics_of_GOB_Chemistry_(Ball_et_al.)/03%3A_Ionic_Bonding_and_Simple_Ionic_Compounds/3.3%3A_Formulas_for_Ionic_Compounds
- J.M. Wright & A. Colling, 1995. Seawater: Its Composition, Properties and Behaviour, p. 29. 2nd edition, Pergamon, Elsevier Science Ltd., Oxford.
- CK-12 Foundation (S. Bewick et al.), 2016. Map: Introductory Chemistry (CK-12), ch. 8.9: Physical Properties of Ionic Compounds. Libre Texts/UC Davis. http://chem.libretexts.org/Textbook_Maps/Introductory_Chemistry_Textbook_Maps/Map%3A_Introductory_Chemistry_(CK-12)/08%3A_Ionic_and_Metallic_Bonding/8.09%3A_Physical_Properties_of_Ionic_Compounds