Expanded Octets

Moderators: Chem_Mod, Chem_Admin

Jessica Yen Dis2G
Posts: 22
Joined: Fri Sep 25, 2015 3:00 am

Expanded Octets

Postby Jessica Yen Dis2G » Mon Oct 19, 2015 5:58 pm

For elements that can have an expanded octet, how can we tell when the atom can no longer take on any more valence electrons? Would the max number of valence electrons an atom with an expanded octet can have equal the 8 valence electrons in the s and p orbitals, plus the amount of electrons in a d orbital (10)? so would the max number of valence electrons an expanded octet can have just be 18 (10+8)?

Ronald Yang 2F
Posts: 86
Joined: Fri Sep 25, 2015 3:00 am

Re: Expanded Octets

Postby Ronald Yang 2F » Mon Oct 19, 2015 9:54 pm

For elements that can have an expanded octet, usually the max number of valence electrons the central atom can take on is the amount of its outer valence electrons. For example, in PCl5, phosphorus has 5 valence electrons, so usually, it can bond with at most 5 other atoms. Again, in XeF6, xenon has 8 valence electrons, so when xenon bonds with 6 fluorine atoms, xenon has a lone pair left over, showing a total of 8 valence electrons (two in the lone pair, 6 used in bonding).

dbalestra4F
Posts: 19
Joined: Fri Sep 25, 2015 3:00 am

Re: Expanded Octets

Postby dbalestra4F » Sat Oct 24, 2015 12:05 pm

So, elements that can expand their octets can only accept the same number of valence electrons they have?
Can someone point to where in the text I can read this?
Thank you!

Ronald Yang 2F
Posts: 86
Joined: Fri Sep 25, 2015 3:00 am

Re: Expanded Octets

Postby Ronald Yang 2F » Fri Oct 30, 2015 10:31 am

Well, usually the most stable structure would be the one with zero formal charge on every atom, which means the central atom would have the same number of electrons closest to it as the number of valence electrons. For example, SF6 can make 6 bonds because it has 6 valence electrons. XeF2 makes 2 bonds(contributes one electron for each bond) and has 3 lone pairs, amounting to 8 electrons. Otherwise, if it were to make more or less, then there would be a formal charge not zero on a certain atom, possibly the central atom when bounded to atoms like halogens. For example, SF5+ would have Sulfur with 5 bonds, making it's formal charge +1, so usually if the central atom deviates from its number of valence electrons, some kind of atom in the molecule has a formal charge other than 0. At least, that's how I think about it.

Emily Steele 4J
Posts: 9
Joined: Wed Sep 21, 2016 2:56 pm

Re: Expanded Octets

Postby Emily Steele 4J » Tue Nov 29, 2016 10:37 am

So just to clarify on this? it can have as many bonds as valence electrons, but it should be arranged to optimize FC?


Return to “Octet Exceptions”

Who is online

Users browsing this forum: No registered users and 1 guest