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Name: John
Status: educator
Grade: 9-12
Location: MO
Country: USA
Date: Spring 2010

I've been teaching about the periodic table recently and I keep getting a question for which my teacher resources provide no clear answer. When discussing elements as either metals or nonmetals, how are the elements commonly grouped as metalloids classified? Also, in what family should astatine be included?

Wikipedia covers his question pretty thoroughly...

Burr Zimmerman

Hi John,

The elements that you refer to that are neither metals nor nonmetals (but that have some characteristics of both) are in fact officially classified as Metalloids. There are, as you probably know, a total of seven of them: Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium and Polonium. Because of their semi-metallic characteristics, at least four of these are used as either the basis for semiconductor devices (Silicon and Germanium), or as so-called "dopant" elements in used in the process to make semiconductor devices (Boron and Arsenic).

Astatine is a little difficult to characterize since it is the rarest element in the earth's crust. Only a few tens of grams of this element are believed to exist naturally. It is highly radioactive and with a half-life of only about 8 hours, and with only trace amounts available, verification of its properties is impossible. Nonetheless, Astatine is classified as a Halogen, and a nonmetal (not a metalloid). Physical properties are expected to be much like Iodine, but even darker in color and less volatile. Chemically, it is expected to act like all the other halogens, but to be less chemically active than Iodine.

Bob Wilson

Hi John

I am not a chemist. I am an engineer, but I have learned how to research questions like this.

So I Googled "Astatine .wiki", and my favorite source, Wikipedia produced this:

This highly radioactive element has been confirmed by mass spectrometers to behave chemically much like other halogens, especially iodine (it would probably accumulate in the thyroid gland like iodine), though astatine is thought to be more metallic than iodine.

So, please check out this URL for the complete story of Astatine:

Here you will find a description of the "characteristics of metals .wiki"

All of the books I have read call radioactive Uranium a metal, And since Astatine is a radioactive element, I would also call it a metal, But Wikipedia is quite the source, being drafted, reviewed, and edited by the entire community. So it is quite the resource. There are also other sources that surface with these searches, some easier to understand than others.

Here are the short answers to your questions:

Q1: When discussing elements as either metals or nonmetals, how are the elements commonly grouped as metalloids classified?

A1: See:

Q2: Also, in what family should astatine be included?

A2: Halogen


Sincere regards,
Mike Stewart

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