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Jedrick Zablan 3L
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Joined: Sat Aug 17, 2019 12:17 am


Postby Jedrick Zablan 3L » Sat Nov 02, 2019 2:11 pm

How do we know which elements typically are exceptions to the octet rule? Do we have to memorize them or is there a specific trend or group in the periodic table?

Astrid Lunde 1I
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Re: Exceptions?

Postby Astrid Lunde 1I » Sat Nov 02, 2019 2:16 pm

The elements in group 3 can break the octet rule.

Abby Soriano 1J
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Joined: Sat Aug 24, 2019 12:16 am

Re: Exceptions?

Postby Abby Soriano 1J » Sat Nov 02, 2019 2:24 pm

The first five elements (H, He, Li, Be, B) can have incomplete octets, as can all group 13 elements. Elements in period 3 and higher can have expanded octet shells because of their d-orbitals.

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Re: Exceptions?

Postby Mashkinadze_1D » Sat Nov 02, 2019 2:24 pm

In general, for exceptions we can imagine what is necessary for the full octet, and for some why they can have more than an octet. For those with an incomplete octet, they are in the boron group and the reason they can form only three bonds is this benefits them as they have three valence electrons only. For anything pas P this can have more than octet due to the fact that there is now a d block that can be used allowing electrons to go into the d suborbital.

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Re: Exceptions?

Postby AnnikaMittelhauser4E » Sat Nov 02, 2019 2:27 pm

As mentioned above, the elements in group 3 can break the octet rule likely by forming an expanded octet. This is because they have access to the unfilled 3d orbitals for bonding. I think other groups above n=2 can also access their respective unfilled d-orbitals to have expanded octets.

Additionally, certain elements (mostly B and Al for our purposes I think) are likely to bond without forming a full octet because they require 5 electrons to make an octet, and those electrons are hard to come by. They commonly form compounds where they have 6 electrons.

Matthew ILG 1L
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Joined: Sat Aug 17, 2019 12:15 am

Re: Exceptions?

Postby Matthew ILG 1L » Sat Nov 02, 2019 2:37 pm

The way I learned in high school, the elements in third period and below are typically allowed to break the octet rule.

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