octet rule

Examples of octet rule in the following topics:

• Odd-Electron Molecules

  • Molecules with an odd number of electrons disobey the octet rule.
  • As the octet rule requires eight electrons around each atom, a molecule with an odd number of electrons must disobey the octet rule.
  • The two oxygen atoms in this molecule follow the octet rule.
  • Nitrogen dioxide is another stable molecule that disobeys the octet rule.
  • It does not obey the octet rule on the nitrogen atom.

• The Incomplete Octet

  • While most elements below atomic number 20 follow the octet rule, several exceptions exist, including compounds of boron and aluminum.
  • However, many atoms below atomic number 20 often form compounds that do not follow the octet rule.
  • These atoms each have three valence electrons, so we would predict that these atoms want to bond covalently in order to gain 5 electrons (through sharing) to fulfill the octet rule.
  • In this compound, the boron atom only has six valence shell electrons, but the octet rule is satisfied by the fluorine atoms.
  • Describe the ways that B, Al, Li, and H deviate from the octet rule

• The Expanded Octet

  • Main group elements in the third period and below form compounds that deviate from the octet rule by having more than 8 valence electrons.
  • As a result, the second period elements (more specifically, the nonmetals C, N, O, F) obey the octet rule without exceptions.
  • Therefore, the d orbitals participate in bonding with other atoms and an expanded octet is produced.
  • For atoms in the fourth period and beyond, higher d orbitals can be used to accommodate additional shared pairs beyond the octet.
  • In the PCl5 molecule, the central phosphorus atom is bonded to five Cl atoms, thus having 10 bonding electrons and violating the octet rule.

• Ionic Bonds

  • The octet rule states that an atom is most stable when there are eight electrons in its valence shell.
  • By satisfying the duet rule or the octet rule, ions are more stable.
  • Both ions form because the ion is more stable than the atom due to the octet rule.
  • This is because Mg has two valence electrons and it would like to get rid of those two ions to obey the octet rule.
  • This is because Mg has two valence electrons and it would like to get rid of those two ions to obey the octet rule.

• Formulas of Ionic Compounds

  • An ionic formula must satisfy the octet rule for the constituent atoms and electric neutrality for the whole compound.
  • The transfer of electrons allows the atoms to effectively achieve the much more stable electron configuration of having eight electrons in the outermost valence shell (octet rule).
  • First, the charge on the constituent ions can be determined based on the transfer of valence electrons necessary in order to satisfy the octet rule.

• Physical Properties of Covalent Molecules

  • These cases of electron sharing can be predicted by the octet rule.
  • The octet rule is a chemical rule that generalizes that atoms of low atomic number (< 20) will combine in a way that results in their having 8 electrons in their valence shells.
  • In a covalent bond, the shared electrons contribute to each atom's octet and thus enhance the stability of the compound.
  • A H atom needs one additional electron to fill its valence level, and the halogens need one more electron to fill the octet in their valence levels.
  • Lewis bonding theory states that these atoms will share their valence electrons, effectively allowing each atom to create its own octet.

• Introduction to Lewis Structures for Covalent Molecules

  • We refer to this chemical tendency of atoms as 'the octet rule,' and it guides us in predicting how atoms combine to form molecules and compounds.
  • These are exceptions to the octet rule because they only require 2 electrons to have a full valence level.
  • It therefore has 7 valence electrons and only needs 1 more in order to have an octet.
  • In order to achieve an octet for all three atoms in CO2, two pairs of electrons must be shared between the carbon and each oxygen.
  • You can see that this is how the octet rule is satisfied for all atoms in this case.

• Formal Charge and Lewis Structure

  • Generally, most Lewis structures follow the octet rule; they will share electrons until they achieve 8 electrons in their outermost valence shell.
  • However, there are exceptions to the octet rule, such as boron, which is stable with only 6 electrons in its valence shell.
  • Most atoms may have an incomplete octet of electrons.
  • However, atoms can share electrons with each other to fulfill this octet requirement.
  • If the octet rule is still not satisfied, atoms may form a double (4 shared electrons) or triple bond (6 shared electrons).

• Borates: Boron-Oxygen Compounds

  • The incomplete octet means that Borates act as Lewis acids.
  • When a trigonal boron atom accepts a pair of electrons from a Lewis base, it adopts a tetrahedral configuration (sp3), and the octet rule is satisfied.

• Covalent Bonds

  • If it shares one electron with a carbon atom (which has four valence electrons), the fluorine will have a full octet (its seven electrons plus the one it is sharing with carbon).
  • Carbon will have to form four single bonds with four different fluorine atoms to fill its octet.
  • The formation of a covalent bond allows the nonmetals to obey the octet rule and thus become more stable.
  • If it shares one electron with a carbon atom (which has four valence electrons), the fluorine will have a full octet (its seven electrons plus the one it is sharing with carbon).
  • Carbon will have to form four single bonds with four different fluorine atoms to fill its octet.