Chemical Bonding: Ionic Bonding

• Compounds are formed when two or more atoms chemically bond together, the resulting compound is unique both chemically and physically from its parent atoms.

·         Ionic bonding: In ionic bonding, (It is called an ionic bond because the atoms become ions, a charged atom that has either lost an electron or has extra electrons) electrons are completely transferred from one atom to another. In the process of either losing or gaining negatively charged electrons, the reacting atoms form ions. The oppositely charged ions are attracted to each other by electrostatic forces, which are the basis of the ionic bond.

For example, during the reaction of sodium with chlorine: Notice that when sodium loses its one valence electron it gets smaller in size, while chlorine grows larger when it gains an additional valence electron. This is typical of the relative sizes of ions to atoms. Positive ions tend to be smaller than their parent atoms while negative ions tend to be larger than their parent.

sodium (on the left) loses its one valence electron to chlorine (on the right),

resulting in

A positively charged sodium ion (left) and a negatively charged chlorine ion (right).

Ionic compounds share many features in common:

• Ionic bonds form between metals and nonmetals.
• In naming simple ionic compounds, the metal is always first, the nonmetal second (e.g., sodium chloride).
• Ionic compounds dissolve easily in water and other polar solvents.
• In solution, ionic compounds easily conduct electricity.
• Ionic compounds tend to form crystalline solids with high melting temperatures. The fact that ionic compounds are solids, results from the intermolecular forces (forces between molecules) in ionic solids.  

Each sodium ion is attracted equally to all of its neighboring chlorine ions, and likewise for the chlorine to sodium attraction. The concept of a single molecule does not apply to ionic crystals because the solid exists as one continuous system. Ionic solids form crystals with high melting points because of the strong forces between neighboring ions.

	Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1
Sodium Chloride Crystal	NaCl Crystal Schematic

·         Elements from opposite ends of the periodic table will generally form ionic bonds. They will have large differences in electron negativity and will usually form positive and negative ions. The elements with the largest electron negativities are in the upper right of the periodic table, and the elements with the smallest electron negativities are on the bottom left. If these extremes are combined, such as in RbF, the dissociation energy is large. As can be seen from the illustration below, hydrogen is the exception to that rule, forming covalent bonds.