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Lewis Structure: Sulfate Ion

October 9, 2012

Video by Janet Gray Coonce MS


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Review the notes after viewing the video:

Now let’s draw the Lewis dot structure for SO4-2.  That means we will have to add 2 electrons into our Lewis dot structure.  So we have a sulfur atom with 4 oxygen atoms surrounding it.  Oxygen is in period 2 and sulfur is in period 3.  Sulfur is directly below oxygen on the periodic table and they are both in group 6ABoth sulfur and oxygen have 6 valence electrons



We begin drawing the Lewis dot structure by drawing the 6 valence electrons around each sulfur and oxygen atom.



In this step we added an extra electron to each of the 2 oxygen atoms as illustrated.  Now all of the electrons are accounted for and 2 of the oxygen atoms are electro-negative.



In this step we drew a single bond between each atom.  The oxygen atoms on the left and right each have 8 valence electrons and are happy Smile  but rather than forming a double bond, each of them have acquired an extra electron which will satisfy the octet rule but will make the atom electro-negative.  This explains the negative 2 charge of the sulfate ion.  The top and bottom oxygen molecule each have an unpaired electron which is available to join in a bond with sulfur.



Here we draw a bond between the unpaired electrons.  If we count the electrons, each of the oxygen atoms have 8 electrons in their valence shell so the octet rule is satisfied.  Sulfur has 12 electrons.  It can do this.  It is called an expanded octetAtoms belonging to period 3 or more may be able to expand the octet.  Let’s re-draw what we have illustrated here.



he two delocalized electrons make multiple resonance structures possible for the sulfate ion (SO4-2). This is the completed Lewis dot structure for one of them.  All 6 of sulfur’s valence electrons are being shared in bonds with oxygen giving a total of 12 valence electrons, an expanded octet.  The sulfur atom is happy Smile with valence shell complete and its formal charge is neutral. 


Transcription by James C. Gray MD FACOG

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