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


Formation of Positive Ions

Metals usually have 1-4 electrons in the outer energy level. The electron arrangement of a rare gas is most easily achieved by losing the few electrons in the newly started energy level. The number of electrons lost must bring the electron number "down to" that of a prior rare gas.

How will sodium complete its octet?

First examine the electron arrangement of the atom. The atomic number is eleven, therefore, there are eleven electrons and eleven protons on the neutral sodium atom. Write the Bohr diagram and Lewis symbol for sodium: (see Graphic on the left)

 This analysis shows that sodium has only one electron in its outer level. The nearest rare gas is neon with 8 electron in the outer energy level. Therefore, this electron is lost so that there are now eight electrons in the outer energy level, and the Bohr diagrams and Lewis symbols for sodium ion and neon are identical. The octet rule is satisfied.

 Ion Charge?

What is the charge on sodium ion as a result of losing one electron? A comparison of the atom and the ion will yield this answer.

 Sodium Atom

 Sodium Ion

 11 p+

 to revert to

 11 p +

 Protons are identical in the atom and ion. Positive charge is caused by lack of electrons.

 12 n

an octet

 12 n

 11 e-

 lose 1 electron

 10 e-

 0 charge

 + 1 charge


An ionic compound is formed by the complete transfer of electrons from a metal to a nonmetal and the resulting ions have achieved an octet. The protons do not change. Metal atoms in Groups 1-3 lose electrons to non-metal atoms with 5-7 electrons missing in the outer level. Non-metals gain 1-4 electrons to complete an octet.


Elemental atoms generally lose, gain, or share electrons with other atoms in order to achieve the same electron structure as the nearest rare gas with eight electrons in the outer level.

The proper application of the Octet Rule provides valuable assistance in predicting and explaining various aspects of chemical formulas.