What happens to a neutral nonmetal atom in order for the octet rule to be satisfied?

1 Answer
Jul 5, 2018

It either gains one or more electrons to form a charged monoatomic ion or share one or more pairs of electrons with another atom.


The nonmetal atom becomes an ion
Nonmetals can receive electrons from a complete electron transfer to form negatively-charged ions. For example, a neutral chlorine atom might gain one electron to form a chloride #"Cl"^(-)# ion:

#"Cl"color(white)(l) + color(white)(l) "e"^(-) to "Cl"^(-)#

The electron added in this process would fill the empty #3p# orbital in the chlorine atom to complete the octet.

  • #"Cl"#: #1s^2 2s^2 2p^2 ul(3s^color(navy)(2) 3p^color(purple)(5)) color(white)(l) color(grey)("incomplete valence shell")#
  • #"Cl"^(-)#: #1s^2 2s^2 2p^2 ul(3s^color(navy)(2) 3p^color(navy)(6)) color(white)(l) color(grey)("extra electron completes the octet")#

The nonmetal atom forms covalent bonds with other atoms
Alternatively, a nonmetal atom might share one or more pairs of electrons with another atom to achieve an octet. Atomic orbitals of the two atoms "overlap" in a way that valence electrons from one atom fill vacancies in electron orbitals of the other.

For example, a hydrogen atom joins a chlorine atom to form a hydrogen chloride molecule.


The chlorine atom has now attained an octet. (Keep in mind that it takes only two valence electrons for a hydrogen atom to achieve the electron configuration of noble gas helium #"H" "e"#, which also contains two electrons. The fact that a hydrogen atom is chemically stable with less than valence eight electrons is an exception to the octet rule).