The octet ascendancy is a principle in chemistry. It permits us to identify the atomic structure of many chemicals. The octet preeminence is also used in identify the names and also formulas for numerous chemicals.

You are watching: Why are hydrogen and helium exceptions to the octet rule

As you might suspect, the octet preeminence is based upon the number 8. The is a direct consequence that the periodic table has actually 8 main columns (the ones close to the top).

The routine table is shown listed below with the key 8 columns the the regular table. This “main” columns are the ones near the optimal of the table.

The number 1-8 shows the number of valence electrons for some atom. Atoms are unstable uneven they have 8 valence electrons. Thus, just the noble gasses are “born” to it is in stable. All various other atoms should gain, lose, or share electron to be much more like a noble gas. Steady atoms often tend to have 8 valence electrons, favor the noble gasses.

The aspects in the reduced columns in the middle do not have actually numbers, and they generally don’t obey the octet rule.


Chlorine dioxide is a an excellent example that a molecule the doesn’t obey the octet rule. The formula because that chlorine dioxide is ClO2, and it’s generally taken to average the chlorine is bonded twice, instead of the normal once. The doesn’t make feeling in regards to the octet rule, together we’d acquire something follow me the lines of 7 + 2 = 9 as soon as counting the chlorine valence electrons. Arg. Yet it’s a real molecule, chlorine dioxide. No all molecules obey the octet rule.

Chlorine dioxide is a bit special in not complying with the octet rule. The strange electron count means that there should be one unpaired electron. This unpaired electron accounts because that the fairly high reactivity the ClO2. As such, chlorine dioxide uses incorporate industrial oxidants and also disinfects for drinking water and also food. The U.S. Food and Drug administration describes generation and application that this relatively common chemical in21CFR173.300. So, it’s failure to follow the octet rule doesn’t make chlorine dioxide bad, rare or useless… it’s a relatively common, important and useful chemical.

Sulfur hexafluoride (SF6) is another molecule that doesn’t obey the octet rule. It has actually sulfur S bonded to 6 fluorine atom F. With two electrons every bond, that renders 12 electrons because that sulfur. That’s a bit an ext than an octet that 8. So, together a rule, occasionally sulfur can kind 6 bonds rather of the typical 2.

See more: How Much Is 5 Pounds Of Crawfish, Whole Cooked Crawfish / 5 Lb Bag

Sulfur hexafluoride, or SF6, is a genuine chemical. It’s supplied as an electrical insulator inside high voltage equipment. Although non-toxic come breathe, SF6canreact to form harmful substances once exposed to certain varieties of electrical discharges. The alsoacts together a greenhouse gaswhen it at some point leaks from electric equipment right into the atmosphere. Although the lacks an octet, i m sorry usually makes molecules stable, SF6isextremely stable. Sulfur hexafluoride is approximated to float around the atmosphere for centuries. Currently that’s a secure molecule!

The above describes just how the octet rule uses to covalent bonds, as uncovered in molecules. There is a whole 2nd case for how the octet dominance apples because that ionic bonds.

Click below to learn about ionic compounds and also the other situation for making use of the octet rule.