What are the criteria for classifying elements as metalloids and halogens?

[thesparrow]

I'm currently studying grade 11 chemistry... And the periodic table of elements slightly confuses me.

I am having trouble understanding which are metalloids, and halogens. In the handout that my teacher gave me, it listed the following as metalloids: B, Si, Ge, As, Sb, Te, Po, and At. It also says the halogens are: F, Cl, Br and I.

On my school agenda, the included periodic table of elements lists the following as metalloids: B, Si, Ge, As, Sb, and Te. It says the halogens are: F, Cl, Br, I, and At.

On Wikipedia, it says these are metalloids: B, Si, Ge, As, Sb, Te and Po. It says the halogens are: F, Cl, Br, I and At.

Which is correct?!

:(

 

[Mike H]

The term "halogen" simply refers to the Group 17 elements as a whole. So as astatine (At) is an element in Group 17 of the periodic table, it can be described as a halogen. Whether something is a metal, non-metal, or metalloid has no impact on this classification. The chalcogens, for example, are all elements in Group 16 (oxygen, sulfur, and so on).

I think people are still arguing over whether polonium and astatine are metalloids in the literature. This is mostly since no one has ever been able to develop any consensus definition of the term. I have the recollection that astatine is more likely to be listed as a non-metal, and that polonium is more likely to be listed as a metalloid, but I would definitely ask your teacher which particular list he or she will be using for the class.