octet exceptions

[Adrienne_4F]

Can someone explain why some of these atoms have octet exceptions? what makes them different from others?

[dgerges 4H]

some exceptions to the octet rule can be found in the 3rd period in the p block because they have an unoccupied d block that lets them expand past the octet rule

[Francis_Nguyen3D]

The first four elements also have octet exceptions where they do not obtain an octet of electrons. This is due to the fact that the first four elements are stable/feel complete with the amount of electrons they currently have.
Another exception would consist of elements such as Boron and Aluminum where they do not require an octet within compounds. This is due to their 3 valence electrons which causes them to only have a total of 6 when bonded. However, they can receive more electrons when bonded with halogens.