When we draw dot-and-cross diagram of a molecule we frequently encounter the instance when the central atom expands octet or have more than 8 electrons around its valence shell.

You are watching: How many valence electrons can sulfur have

Which room the aspects that are qualified of law that?

An aspect from duration 3 and also below will be able to expand octet by making usage of that is energetically accessible, or short lying d-subshell because that bonding.

This way only duration 2 aspects such as C, N, O and also F cannot expand octet and also have to obey octet rule.

expansion of octet dominance guidelines

Take keep in mind octet dominion is the exception and also not the norm, as many of the elements in the regular Table are duration 3 and also beyond, so because of this can increase octet if necessary.

Let"s consider the electronic configuration that oxygen, a period 2 element.

expansion the octet duration 2 example oxygen

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

In gaianation.netplete oxygen will have actually 4 electrons from the 2 bonds and 4 electron from the 2 lone bag which adds approximately 8 electrons.

Hence oxygen is octet and also obeys octet rule.

How around sulfur, the period 3 facet directly below oxygen?

expansion that octet period 3 instance sulfur octet

Notice the for sulfur it has actually 3d subshell i beg your pardon is really close in state of power level as contrasted to 3s and also 3p subshells due to the fact that they are all in the same primary quantum shell.

Sulfur can make use of its 2 unpaired electrons to form 2 covalent bonds plus the 4 electrons from that is 2 lone pairs to offer a gaianation.netplete of 8 electrons.

Hence sulfur obeys octet ascendancy in this case.

But sulfur have the right to unpair that is electrons and promote among its electron (highlighted in green) gaianation.nete an empty 3d orbital.

This process is referred to as excitation since 3d subshell is higher in power hence energy is gaianation.netpelled to move an electron indigenous 3p gaianation.nete 3d subshell.

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

expansion of octet duration 3 example sulfur broaden octet 10 electrons

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

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

Sulfur has one an ext electron pair in its 3s subshell for this reason it deserve to undergo excitation one an ext time and place the electron in one more empty 3d orbital.

expansion that octet duration 3 example sulfur expand octet 12 electrons

Now sulfur has actually 6 unpaired electron which method it can form 6 covalent binding to offer a full of 12 electrons about its valence shell.

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

The driving force for excitation is the unpairing of electron will permit the facet to type more covalent bonds, hence an ext energy is released from the development of an ext bonds, and also the last configuration will certainly be an ext stable.

So why wouldn"t duration 2 facets such together oxygen undergo excitation?

expansion that octet why oxygen cannot increase octet

This is since the next accessible orbital because that unpairing of electrons is in 3s subshell, i beg your pardon is in the following principal quantum shell.

The energy difference is too big and it requires too much initiative for oxygen to unpair that is electron and also promote it gaianation.nete the 3s subshell.

Hence oxygen and also other period 2 elements do not usage orbitals in the 3rd principal quantum covering for bonding and cannot expand octet.

For the thorough 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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