Beryllium exception

[Jessica Lutz 2E]

In 3.67, the central Beryllium atom in BeCl2 is allowed to only have 4 electrons. Why is this an exception?

[sandros]

Beryllium and lithium both form a duplet instead of forming an octet. This is mainly related to the fact that the energy required to give Li and Be a full octet is much higher than the energy required to give up one or two electrons and form a duplet (the same way as helium does).

[Suhail Zaveri]

This is only because beryllium only has 4 valence electrons, it does not have enough electrons in order to fulfill the octet rule, therefore it does not follow the octet rule due to limited electrons.

[Rachel N 1I]

There are also multiple exceptions to the octet rule including boron and aluminum

[Clarissa Molina 1D]

Are Be and Li the only atoms that form duplets or do other atoms form duplets as well?