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elements that do not obey the octet rule

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xiankai:
after finally getting into college, im getting pumped up learning new stuff, havent been around here alot. during a recent lecture about chemical bonding, i came across BeCl2, BCl3, PCl5, SF6, the examples illustrated in the lecture.

what was interesting is the way that the electrons were structured. BeCl2 lacks 4 e- for the Be atom, so it has 1s2 2s2 2p2 and BCl3 lacks 2 e- for the B atom and thus has 1s2 2s2 2p4. what makes these compounds stable? does their electron deficiency affect their stability in any way?

then about PCl5 and SF6. i learnt that the reason that they can possess more than 8 electrons due to the empty energetically accessible 3d subshell. but what is curious is the way the electrons are "restructured". for example

P in PCl5 = 1s2 2s2 2p6 3s2 3p3 --> 1s2 2s2 2p6 3s2 3p6 3d2

let us take into account the valence electrons only for convenience's sakes, where ( = left spin e-, ) = right spin e-

3s2 3p3 () ( ( (

becomes

3s1 3p3 3d1 ( ( ( ( (

and with shared electrons

3s2 3p6 3d2 () () () () ()

how does the e- from the 3s2 orbital jump up to the 3d1 orbital in the first place? surely such a drastic jump requires alot of energy...

Mitch:

--- Quote ---i learnt that the reason that they can possess more than 8 electrons due to the empty energetically accessible 3d subshell.
--- End quote ---

That is completely and totally wrong. Go to your professor and hit them on the back side of their head. Tell him you are a Chemist and you want to know the real Molecular Orbital Theory for what is going on. 3d Orbitals do not need to be invoked at all!

Donaldson Tan:
hint: Be is in period 2. P is in period 3.

billybo:
how about BeH3... Does that have any exceptions because it has too few electrons to bond to 3 Hs.

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