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Video transcript

let's do one more example of constructing a Lewis diagram that might be a little bit interesting so let's say we want to construct the Lewis structure or Lewis diagram for xenon difluoride so pause this video and have a go of that all right now let's work through this together so first step we just have to account for the valence electrons xenon right over here it is a noble gas it has eight valence electrons one two three four five six seven eight in that fifth shell it's in the fifth period so it has eight valence electrons and then fluorine we have looked at fluorine multiple times we know that it has seven valence electrons one two three four five six seven in that second shell and we have two of these fluorines so two times seven and then this gives us a total of 8 plus 14 valence electrons which gets us to 22 valence electrons in total now the next step and we've done this multiple times in multiple videos now is we would try to draw the structure with some single covalent bonds and we would put xenon as our central atom because it is less electronegative than fluorine so let's put a xenon there and let's put two fluorines on either side so fluorine there and a fluorine there and let's set up some single covalent bonds and so how many of our valence electrons have we now accounted for well two in that in that bond and then two in that bond so we've accounted for four so minus four valence electrons we now have a total of 18 valence electrons now the next step is we want to allocate them to our terminal atoms and try to get them to a full octet each of these fluorines already have two valence electrons that they are sharing so we need to give each of them six more so two four six two for six so I've just allocated 12 more valence electrons so minus 12 valence electrons means that we still have six valence electrons left to allocate and there's only one place where we can allocate those leftover six valence electrons and that's at the central atom at the Xenon so let's do that so two four and six and there you have it we have the Lewis diagram the lewis structure for xenon difluoride now what's interesting here is our fluorines they have an octet of valence electrons but what's going on with Zenon Zenon has 2 4 6 8 10 valence electrons hanging around so this is one of those examples of an exception to the octet rule where we go beyond eight valence electrons which is possible for elements in the third or higher period
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