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 right)

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


A positive ion is formed by the loss of negatively charged electrons. Although the number of protons does not change in the ion, there is an excess number of protons over electrons which produces the positive charge. All electrons in the outer energy level are lost.

Octet Rule: 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.