Phosphate

[Algernon Jackson 2l]

Why is phosphate an exception to the octet rule?

[JoshMoore2B]

Why is phosphate an exception to the octet rule?

It isn't that phosphate itself is an exception to the octet rule, but rather that the phosphorus in the phosphate acts as an exception to the octet rule to create the compound. This is because the phosphorus has access to the 3d orbital, and so it can take on more bonds (in the case of phosphate, 5 instead of the 3 expected by its group) because it is able to store more than 8 electrons in its valence shell, which is called an expanded octet.

[Thomas Vu 1A]

Just to add on, any atom starting with period 3 and beyond (with the exception of Na+ and Mg I think) will be able to have an expanded octet because of access to that 3d orbital.

[shevanti_kumar_1E]

Phosphate can have an expanded octet because it can accommodate more than 8 valence electrons. Atoms in periods 3 or greater have d orbitals in valence shell that can accommodate additional electrons. An example is phosphorus pentachloride (PCl5). In this molecule P has an expanded octet and bonds with 5 Cl.

[rhettfarmer-3H]

Phosphate can have an extended octet because it is the first row of p block before the introduction of the 3d block. Therefore, it is open to be used. Hence, that is why phosphorus and elements in the p block below the 3 p are able to open and sue the 3d block. Also, it is low energy so it's not too taxing for stability.

[AlbertGu_2C]

Phosphate is in the 3p orbital, so it has access to the 3d orbital of electrons, so it can fill that shell to compensate.

[Jasraj Parmar 3H]

Phosphate is in period 3 so it can have an expanded octet and hold up to 18 electrons theoretically.

[Gian Boco 2G]

Phosphate has access to the 3d state, which means it can add extra valence electrons