When we attract dot-and-cross diagram of a molecule we frequently encounter the case when the central atom increases octet or have much more than 8 electrons approximately its valence shell.

You are watching: How many electrons does sulfur need to be stable

Which are the aspects that are capable of law that?

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

This means only period 2 facets such together C, N, O and also F cannot broaden octet and have to obey octet rule.

expansion the octet dominion guidelines

Take keep in mind octet rule is the exception and not the norm, as most of the aspects in the regular Table are duration 3 and beyond, so thus can increase octet if necessary.

Let"s think about the digital configuration the oxygen, a period 2 element.

expansion of octet period 2 instance oxygen

From the electron-in-box diagram we can see the oxygen has 2 unpaired electron so can kind 2 covalent bonds.

In complete oxygen will have 4 electron from the 2 bonds and 4 electrons from that 2 lone pairs which adds up to 8 electrons.

Hence oxygen is octet and also obeys octet rule.

How around sulfur, the period 3 element directly listed below oxygen?

expansion the octet duration 3 instance sulfur octet

Notice that for sulfur it has 3d subshell which is an extremely close in state of energy level together centregalilee.compared come 3s and also 3p subshells since they room all in the same principal quantum shell.

Sulfur can manipulate its 2 unpaired electron to form 2 covalent bonds plus the 4 electrons from its 2 lone pairs to offer a total of 8 electrons.

Hence sulfur obeys octet dominion in this case.

But sulfur deserve to unpair the electrons and also promote one of its electrons (highlighted in green) come an empty 3d orbital.

This procedure is called excitation since 3d subshell is higher in power hence energy is required to move an electron from 3p to 3d subshell.

Since the power difference in between subshells in the same major quantum covering is small, it requires very tiny energy for excitation to take it place.

expansion of octet duration 3 instance sulfur increase octet 10 electrons

After excitation we have the right to see that there are now 4 unpaired electrons which way sulfur have the right to now type 4 covalent bonds plus 1 lone pair which will offer a complete of 10 electron in that valence shell.

Since sulfur currently has more than 8 electrons, we say that it "expands octet".

Sulfur has actually one much more electron pair in that 3s subshell therefore it deserve to undergo excitation one much more time and place the electron in an additional empty 3d orbital.

expansion the octet period 3 instance sulfur expand octet 12 electrons

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

So in addition to being octet, sulfur can broaden octet to have 10 or 12 electrons.

The driving pressure for excitation is the unpairing of electron will permit the aspect to form more covalent bonds, hence an ext energy is exit from the development of much more bonds, and also the final configuration will be much more stable.

So why wouldn"t period 2 facets such as oxygen undergo excitation?

expansion of octet why oxygen cannot increase octet

This is due to the fact that the next easily accessible orbital because that unpairing of electron is in 3s subshell, i m sorry is in the next principal quantum shell.

The energy difference is too large and it calls for too much effort for oxygen come unpair the electron and promote it come the 3s subshell.

Hence oxygen and other duration 2 facets do not use orbitals in the third principal quantum covering for bonding and also cannot broaden octet.

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For the thorough step-by-step discussion on how duration 3 elements expand octet, check out this video!

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

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