When we attract dot-and-cross diagram of a molecule we often encounter the situation when the central atom increases octet or have an ext than 8 electrons around its valence shell.

You are watching: Can oxygen have an expanded octet

Which are the elements that are capable of act that?

An facet from period 3 and also below will have the ability to expand octet by making use of the energetically accessible, or low lying d-subshell because that bonding.

This way only period 2 elements such together C, N, O and F cannot expand octet and also have to follow octet rule.

expansion of octet rule guidelines

Take keep in mind octet rule is the exception and also not the norm, as many of the aspects in the periodic Table are duration 3 and beyond, so because of this can broaden octet if necessary.

Let"s take into consideration the digital configuration the oxygen, a duration 2 element.

expansion that octet period 2 example oxygen

From the electron-in-box diagram we have the right to see the oxygen has actually 2 unpaired electrons so can type 2 covalent bonds.

In total oxygen will have actually 4 electrons from the 2 bonds and also 4 electrons from that is 2 lone pairs which adds approximately 8 electrons.

Hence oxygen is octet and obeys octet rule.

How about sulfur, the period 3 element directly below oxygen?

expansion that octet duration 3 instance sulfur octet

Notice that for sulfur it has 3d subshell which is an extremely close in terms of energy level as ptcouncil.netpared come 3s and 3p subshells due to the fact that they space all in the same primary quantum shell.

Sulfur can make use of its 2 unpaired electron to kind 2 covalent bonds add to the 4 electron from its 2 lone bag to provide a total of 8 electrons.

Hence sulfur obeys octet dominion in this case.

But sulfur deserve to unpair its electrons and also promote among its electrons (highlighted in green) to an north 3d orbital.

This process is called excitation due to the fact that 3d subshell is higher in power hence energy is compelled to move an electron from 3p to 3d subshell.

Since the power difference between subshells in the same major quantum shell is small, it calls for very little energy for excitation to take place.

expansion the octet period 3 instance sulfur broaden octet 10 electrons

After excitation we can see the there are currently 4 unpaired electrons which method sulfur have the right to now form 4 covalent bonds add to 1 lone pair i m sorry will provide a full of 10 electrons in that valence shell.

Since sulfur now has an ext than 8 electrons, we say the it "expands octet".

Sulfur has actually one an ext electron pair in that is 3s subshell so it have the right to undergo excitation one an ext time and also place the electron in another empty 3d orbital.

expansion of octet period 3 instance sulfur broaden octet 12 electrons

Now sulfur has actually 6 unpaired electron which method it can type 6 covalent binding to give a complete of 12 electrons roughly its valence shell.

So in enhancement to gift octet, sulfur can broaden octet to have 10 or 12 electrons.

The driving pressure for excitation is the unpairing of electrons will allow the element to form more covalent bonds, hence much more energy is exit from the formation of an ext bonds, and the final configuration will certainly be more stable.

So why wouldn"t duration 2 facets such as oxygen experience excitation?

expansion the octet why oxygen cannot expand octet

This is due to the fact that the next accessible orbital for unpairing of electron is in 3s subshell, i beg your pardon is in the following principal quantum shell.

The energy distinction is too big and it needs too much initiative for oxygen come unpair its electron and also promote it come the 3s subshell.

Hence oxygen and other period 2 aspects do not use orbitals in the third principal quantum covering for bonding and cannot expand octet.

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For the detailed step-by-step conversation on how duration 3 elements expand octet, examine out this video!

Topic: chemical Bonding, physical Chemistry, A Level Chemistry, Singapore

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