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 Ionic Compounds
Sodium Fluoride

How do atoms of elements form ionic compounds?

The Octet Rule is the basis for the predictions about the charges on ions. Ionic compounds are formed as the result of the formation of positive and negative ions. Electrons are actually transferred from one atom to another to form rare gas electron structures for each ion. The atom which forms a positive ion loses electrons to the atom which gains electrons to form a negative ion. A compound is not stable unless the number of electrons which are lost and gained are equal . Summary Principle of Ionic Compounds.

Example: Determine the formula of a compound formed by the reaction of sodium and fluoride.


First examine the electron arrangement of the sodium and fluorine atoms.


 Atomic No.
 Bohr diagram

 Group No.
 Lewis Dots



 2 - 8 - 1





 2 - 7



Write the Lewis symbol for each atom. See Graphic on the left.

Determine the numbers of electrons which the atoms will lose and gain by applying the Octet Rule. Na loses one electron to have an octet. Fluorine gains one electron to have an octet.

Formation of Positive Ion: After the electron is lost by sodium, it becomes it becomes a positive ion. (11 p + 10 e- = +1).

Formation of Negative Ion: After fluorine gains the electron from sodium, it becomes a negatively charged ion. (9 p + 10 e- = -1).

The ionic bond between ions results from the electrostatic attraction of opposite charges.

The final formula of sodium fluoride is NaF.


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.