View source for Octet rule

The number of dots you have around the [[Lewis electron-dot symbols of elements]] represents the actual number of valence electrons for the element. 

Elements belonging to Group VIIIA are called the  noble gases. These elements have 8  [[Lewis electron-dot symbols of elements#Symbol|valence electrons]] and are said to have a complete octet of electrons. This is the equivalent of a filled energy level, or a closed shell. This special arrangement of EIGHT electrons makes the noble gases relatively unreactive. Although Helium is the only noble gas with two valence electrons, you will recall that the first energy level can only accommodate two electrons. 

A thorough understanding of the Rule of Eight or the '''Octet Rule''' is essential for further study involving chemical bonding of atoms and the formation of compounds. It turns out that in the formation of molecules from atoms, most atoms attempt to achieve this configuration of 8 valence electrons around each atom. In order to achieve this, atoms tend to lose or gain electrons to ions in order to achieve an octet of electrons.

==Ion formation==

{| border=1 cellpadding="5" align="center"
!scope="col"|Group
!scope="col"|Number of valence electrons 
!scope="col"|Gain or lose electrons
!scope="col"|Charge of ions 
!scope="col"|Examples	
|-
|align="center"|IA
|align="center"|1
|align="center"|lose 1 electron
|align="center"| +1
|align="center"|H<sup>+</sup>, Li<sup>+</sup>, Na<sup>+</sup>, K<sup>+</sup>
|-
|align="center"|IIA
|align="center"|2
|align="center"|lose 2 electrons
|align="center"| +2
|align="center"|Mg<sup>+2</sup>, Ca<sup>+2</sup>, Sr<sup>+2</sup>
|-
|align="center"|IIIA
|align="center"|3
|align="center"|lose 3 electrons
|align="center"| +3
|align="center"|Al<sup>+3</sup>, Ga<sup>+3</sup>
|-
|align="center"|IVA
|align="center"|4
|align="center"|lose 4 electrons<br />gain 4 electrons
|align="center"| +4<br />-4
|align="center"|Sn<sup>+4</sup>, Pb<sup>+4</sup><br />C<sup>-4</sup>
|-
|align="center"|VA
|align="center"|5
|align="center"|gain 3 electrons
|align="center"| -3
|align="center"|N<sup>-3</sup>, P<sup>-3</sup>
|-
|align="center"|VIA
|align="center"|6
|align="center"|gain 2 electrons
|align="center"| -2
|align="center"|O<sup>-2</sup>, S<sup>-2</sup>
|-
|align="center"|VIIA
|align="center"|7
|align="center"|gain 1 electron
|align="center"| -1
|align="center"|F<sup>-</sup>, Cl<sup>-</sup>
|-
|align="center"|VIIIA
|align="center"|8
|colspan="3" align="center"|Complete octet makes the noble gases unreactive
|}

==Number of bonds==
The location of an element in the periodic table allows us to predict the number of covalent bonds that it can form.  When an element forms a bond with another element, a line is drawn to represent the sharing of a pair of electrons between the two elements.

* Hydrogen belonging to '''Group IA''' has '''one''' valence electron, shares this valence electron with another atom to form '''one''' covalent bond.
{| border=1 align="center" width="450"
! Electron - Dot Symbol
! Covalent Bonding
! Number of Covalent Bond
|-
|align="center"|[[File:edot_H.gif]]
|align="center"|[[File:edot_H_bond.gif]]
|align="center"|1
|}
* Boron belonging to '''Group IIIA''' has '''three''' valence electrons, shares its valence electrons with other atoms to form '''three''' covalent bonds.
{| border=1 align="center" width="450"
! Electron - Dot Symbol
! Covalent Bonding
! Number of Covalent Bond
|-
|align="center"|[[File:edot_B.gif]]
|align="center"|[[File:edot_B_bond.gif]]
|align="center"|3
|}
* Carbon and Silicon belonging to '''Group IVA''' have '''four''' valence electrons, shares their valence electrons with other atoms to form '''four''' covalent bonds.
{| border=1 align="center" width="450"
! Electron - Dot Symbol
! Covalent Bonding
! Number of Covalent Bond
|-
|align="center"|[[File:edot_C.gif]]
|align="center"|[[File:edot_C_bond.gif]]
|align="center"|4
|-
|align="center"|[[File:edot_Si.gif]]
|align="center"|[[File:edot_Si_bond.gif]]
|align="center"|4
|}
* Nitrogen and Phosphorus belonging to '''Group VA''' has '''five''' valence electrons, shares three of its '''five''' valence electrons with other atoms to form three covalent bonds. The other two valence electrons form one nonbonding electron pair.
{| border=1 align="center" width="450"
! Electron - Dot Symbol
! Covalent Bonding
! Number of Covalent Bond
|-
|align="center"|[[File:edot_N.gif]]
|align="center"|[[File:edot_N_bond.gif]]
|align="center"|3
|-
|align="center"|[[File:edot_P.gif]]
|align="center"|[[File:edot_P_bond.gif]]
|align="center"|3
|}
* Oxygen and Sulfur belonging to '''Group VIA''' has '''six''' valence electrons. These elements need two valence electrons to complete an octet of electrons. They share two of the six valence electrons with other atoms to form two covalent bonds. The other four valence electrons form two nonbonding electron pair.
{| border=1 align="center" width="450"
! Electron - Dot Symbol
! Covalent Bonding
! Number of Covalent Bond
|-
|align="center"|[[File:edot_O.gif]]
|align="center"|[[File:edot_O_bond.gif]]
|align="center"|2
|-
|align="center"|[[File:edot_S.gif]]
|align="center"|[[File:edot_S_bond.gif]]
|align="center"|2
|}
* Fluorine, Chlorine, Bromine and Iodine belonging to '''Group VIIA''' has '''seven''' valence electrons. These elements need '''one''' valence electron to complete an octet of electrons. They share one of the seven valence electrons with other atoms to form one covalent bond. The other six valence electrons form three nonbonding electron pair.
{| border=1 align="center" width="450"
! Electron - Dot Symbol
! Covalent Bonding
! Number of Covalent Bond
|-
|align="center"|[[File:edot_F.gif]]
|align="center"|[[File:edot_F_bond.gif]]
|align="center"|1
|-
|align="center"|[[File:edot_Cl.gif]]
|align="center"|[[File:edot_Cl_bond.gif]]
|align="center"|1
|-
|align="center"|[[File:edot_Br.gif]]
|align="center"|[[File:edot_Br_bond.gif]]
|align="center"|1
|-
|align="center"|[[File:edot_I.gif]]
|align="center"|[[File:edot_I_bond.gif]]
|align="center"|1
|}

==Exceptions to the Octet Rule==

There are exceptions to the Octet rule for atoms below period two.

* Boron and aluminum compounds commonly have six electrons around the metal center (eg AlH<sub>3</sub>, BH<sub>3</sub>). Compounds with less than an octet around each atom are called electron deficient. Part of this is due to their low electronegativity properties.
* Phosphorus and Sulfur have a tendency to exceed their octets (eg PF<sub>5</sub>, SF<sub>6</sub>). Phosphorus and sulfur expand their octets to accommodate more than eight electrons because they have empty 3d orbitals.

The Octet Rule is a simplistic view on the concept of bonding. Molecular Orbital Theory provides a better description of the complexity of molecular bonding.


==Content suitability==
BCIT courses:
<span class="pops">[http://www.bcit.ca/study/outlines/chem0011  CHEM 0011]</span>