Formulas, the Octet Rule, and Ionic Bonds

As mentioned previously, in 1916, Lewis noted that noble gases were particularly stable and did not form compounds. Lewis used these facts to formulate the octet rule. The noble gases have their outer electron shell filled with eight electrons. (Helium is an exception with only two electrons in its outer shell.) The octet rule says that the most stable electron configuration of an atom occurs when that atom acquires the valence electron configuration of a noble gas. That is, when an atom can acquire eight (octet) electrons in its valence shell (or two for hydrogen to become like helium). 

We can use Lewis dot formulas to represent the transfer of electrons in the formation of ionic compounds. For example, the formation of the ionic compound sodium fluoride, NaF, can be represented using Lewis dot formulas and valence electron conflgurations  

Sodium donates an electron to fluorine, and in the process, sodium becomes the sodium ion, Na+, and fluorine becomes the fluoride ion, F. The net outcome of the transfer of an electron in this case results in both sodium and fluorine obtaining a valence electron configuration similar to the noble gas neon. The Na+ and F are held together by the electrostatic attraction between the oppositely charged ions. 

More than a single electron may be transferred when an ionic bond is formed. Two examples of ionic compound formation involving the transfer of more than one electron are the formation of calcium chloride and magnesium oxide  

In the first reaction, a single calcium atom donates two electrons to two chlorine atoms. This results in the formation of a Ca + ion and two Cl ions. The positive ion and two negative ions are attracted to each other. In the formation of magnesium oxide, magnesium donates two electrons to oxygen resulting in Mg and 

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