Simple Compounds Covalent Compounds  Elmhurst College
Positive Ions Sodium Fluoride  Magnesium Oxide  Chemistry Department
Negative Ions Iron Oxide Review Covalent/Ionic Cpds  Virtual ChemBook


 Introduction to Ionic Compounds


Those molecules that consist of charged ions with opposite charges are called IONIC. These ionic compounds are generally solids with high melting points and conduct electrical current. Ionic compounds are generally formed from metal and a non-metal elements. See Ionic Bonding below.

Ionic Compound Example:

For example, you are familiar with the fairly benign unspectacular behavior of common white crystalline table salt (NaCl). Salt consists of positive sodium ions (Na+) and negative chloride ions (Cl-). On the other hand the element sodium is a silvery gray metal composed of neutral atoms which react vigorously with water or air. Chlorine as an element is a neutral greenish-yellow, poisonous, diatomic gas (Cl2).

The main principle to remember is that ions are completely different in physical and chemical properties from the neutral atoms of the element .

The notation of the + and - charges on ions is very important as it conveys a definite meaning. Whereas elements are neutral in charge, IONS have either a positive or negative charge depending upon whether there is an excess of protons (positive ion) or excess of electrons (negative ion).

Formation of Positive Ions.
Formation of Negative Ions.

Introduction to Ionic Bonding:

Ionic bonding is best treated using a simple electrostatic model . The electrostatic model is simply an application of the charge principles that opposite charges attract and similar charges repel. An ionic compound results from the interaction of a positive and negative ion, such as sodium and chloride in common salt.

The IONIC BOND results as a balance between the force of attraction between opposite plus and minus charges of the ions and the force of repulsion between similar negative charges in the electron clouds. In crystalline compounds this net balance of forces is called the LATTICE ENERGY. Lattice energy is the energy released in the formation of an ionic compound.

DEFINITION: The formation of an IONIC BOND is the result of the transfer of one or more electrons from a metal onto a non-metal.

 Metals, with only a few electrons in the outer energy level, tend to lose electrons most readily. The energy required to remove an electron from a neutral atom is called the IONIZATION POTENTIAL.

Energy + Metal Atom ---> Metal (+) ion + e-

 Non-metals, which lack only one or two electrons in the outer energy level have little tendency to lose electrons - the ionization potential would be very high. Instead non-metals have a tendency to gain electrons. The ELECTRON AFFINITY is the energy given off by an atom when it gains electrons.

Non-metal Atom + e- --- Non-metal (-) ion + energy

 The energy required to produce positive ions (ionization potential) is roughly balanced by the energy given off to produce negative ions (electron affinity). The energy released by the net force of attraction by the ions provides the overall stabilizing energy of the compound.