Exceptions?

[Jedrick Zablan 3L]

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]

The elements in group 3 can break the octet rule.

[Abby Soriano 1J]

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.

[Mashkinadze_1D]

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.

[AnnikaMittelhauser4E]

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]

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