octet rule

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Agustina Santa Cruz 2F
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Joined: Wed Sep 30, 2020 10:01 pm

octet rule

Postby Agustina Santa Cruz 2F » Sun Nov 08, 2020 4:36 pm

How do we know if the octet rule should be followed or not? When is it allowed to be broken?

Khoa Vu 3l
Posts: 86
Joined: Wed Sep 30, 2020 9:59 pm

Re: octet rule

Postby Khoa Vu 3l » Sun Nov 08, 2020 4:50 pm

The three examples of violations to the octet rule we have talked about in class so far are electron-deficient molecules, radicals, and elements with an expanded octet. Typical electron-deficient elements, like Boron and Aluminum (Group 13 elements) with 3 valence electrons would need to gain an additional 5 electrons to fulfill their octet, which is too many, so in compounds like BF3 and AlCl3, they are left with only six valence electrons, which they can gain from coordinate covalent bonds (electron pairs donated from the same atom). For example, Boron in BF3 can satisfy its octet through F- and the lone pair on NH3. Radicals are compounds with an unpaired e-, an odd number of electrons, 7. Radicals are typically highly reactive, such as •CH3 or OH and •H (derived from a photon hitting a water molecule). Lastly, elements with an expanded octet can occur for elements found in the third period or later (n=3) because they would have access to empty d-orbitals to allow for more than the typical 8 electrons found in the octet.

Arnav Saud 2C
Posts: 111
Joined: Wed Sep 30, 2020 9:51 pm

Re: octet rule

Postby Arnav Saud 2C » Sun Nov 08, 2020 4:51 pm

Concerning the octet rule, there are 3 scenarios where the octet rule can be violated. The three are odd-electron molecules, electron-deficient molecules, and expanded valence shell molecules.
Odd election molecules like NO (look up its lewis structure) have 11 electrons which causes an extra electron to be in the molecule.
Electron deficient molecules are stable molecules that have less than 8 electrons around an atom in a molecule. An example is BF3.
Expanded valence shell molecules are found compounds with more than eight electrons assigned to their valence shell. They're only formed by central atoms in the third row of the periodic table or beyond that have empty d orbitals in their valence shells that can participate in covalent bonding. An example of this is PF5.

Heather Szeszulski 1I
Posts: 59
Joined: Wed Sep 30, 2020 9:55 pm

Re: octet rule

Postby Heather Szeszulski 1I » Sun Nov 08, 2020 6:14 pm

Khoa Vu 2B wrote:The three examples of violations to the octet rule we have talked about in class so far are electron-deficient molecules, radicals, and elements with an expanded octet. Typical electron-deficient elements, like Boron and Aluminum (Group 13 elements) with 3 valence electrons would need to gain an additional 5 electrons to fulfill their octet, which is too many, so in compounds like BF3 and AlCl3, they are left with only six valence electrons, which they can gain from coordinate covalent bonds (electron pairs donated from the same atom). For example, Boron in BF3 can satisfy its octet through F- and the lone pair on NH3. Radicals are compounds with an unpaired e-, an odd number of electrons, 7. Radicals are typically highly reactive, such as •CH3 or OH and •H (derived from a photon hitting a water molecule). Lastly, elements with an expanded octet can occur for elements found in the third period or later (n=3) because they would have access to empty d-orbitals to allow for more than the typical 8 electrons found in the octet.


Should we be expected to memorize this? Also does anyone have good resources to understand the concept better?

Madison Muggeo 3H
Posts: 90
Joined: Wed Sep 30, 2020 9:35 pm

Re: octet rule

Postby Madison Muggeo 3H » Sun Nov 08, 2020 6:56 pm

Someone in the GroupMe mentioned organic chemistry tutor on Youtube? I'm not too familiar with him but others seem to like his videos. Also, I would assume that we do have to memorize these.

Tobie Jessup 2E
Posts: 84
Joined: Wed Sep 30, 2020 10:02 pm

Re: octet rule

Postby Tobie Jessup 2E » Sun Nov 08, 2020 9:18 pm

Khoa Vu 2B wrote:The three examples of violations to the octet rule we have talked about in class so far are electron-deficient molecules, radicals, and elements with an expanded octet. Typical electron-deficient elements, like Boron and Aluminum (Group 13 elements) with 3 valence electrons would need to gain an additional 5 electrons to fulfill their octet, which is too many, so in compounds like BF3 and AlCl3, they are left with only six valence electrons, which they can gain from coordinate covalent bonds (electron pairs donated from the same atom). For example, Boron in BF3 can satisfy its octet through F- and the lone pair on NH3. Radicals are compounds with an unpaired e-, an odd number of electrons, 7. Radicals are typically highly reactive, such as •CH3 or OH and •H (derived from a photon hitting a water molecule). Lastly, elements with an expanded octet can occur for elements found in the third period or later (n=3) because they would have access to empty d-orbitals to allow for more than the typical 8 electrons found in the octet.


I was also struggling with this concept but this response was super helpful thanks so much!

Chinmayi Mutyala 3H
Posts: 90
Joined: Wed Sep 30, 2020 9:50 pm

Re: octet rule

Postby Chinmayi Mutyala 3H » Sun Nov 08, 2020 11:25 pm

There are certain times when it can be violated such as P and I which are exceptions because they have an expanded valence orbital. These are just exceptions we'll have to memorize.

Jerry_T
Posts: 89
Joined: Wed Sep 30, 2020 9:46 pm

Re: octet rule

Postby Jerry_T » Sun Nov 08, 2020 11:55 pm

The octet rules applies to the first three rows of the periodic table if I remember correctly. (Correct me if I'm wrong please)


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