Duet rule, for hydrogen

Arrange the remaining electrons around the atoms to satisfy the duet rule for hydrogen and the octet rule for other atoms. 

Lewis structures are drawn to represent the arrangement of the valence electrons in a molecule. The rules for drawing Lewis structures are based on the observation that nonmetal atoms tend to achieve noble gas electron configurations by sharing electrons. This leads to a duet rule for hydrogen and to an octet rule for many other atoms. 

Example 1 Write the electronic formula for CH4O which satisfies the covalency requirements and the octet rule (duet rule for hydrogen). 

Hydrogen forms stable molecules where it shares two electrons. That is, it follows a duet rule. For example, when two hydrogen atoms, each with one electron, combine to form fhe H2 molecule, we have... 

These examples illustrate the principle that atoms in covalently bonded species tend to have noble-gas electronic structures. This generalization is often referred to as the octet rule. Nonmetals, except for hydrogen, achieve a noble-gas structure by sharing in an octet of electrons (eight). Hydrogen atoms, in molecules or polyatomic ions, are surrounded by a duet of electrons (two). 

In drawing Lewis structures for covalently bonded molecules, the octet rule is used as a guide (remember that for hydrogen the octet is changed to a duet). Shared electrons count toward the electron total for both atoms in the bond. For example, the Lewis structure for SiH4 looks like this ... 

The hydrogen atom duets are satisfied, but we would need two additional electrons to satisfy the octet rule for the carbon atoms. Since these are not available, we can satisfy the octet rule by adding the two remaining electrons as another pair between the carbon atoms to form what is called a double bond ... 

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