Question about monoisotopic elements

[marc32123]

Question about monoisotopic elements...

Of the 80 elements with at least one stable isotope, 26 have only one single stable isotope. The mean number of stable isotopes for the 80 stable elements is 3.1 stable isotopes per element. The largest number of stable isotopes that occur for a single element is 10 (for tin, element 50).

What does it mean for an element to have only one single stable isotope? I don't quite get it. I read that beryllium has only one stable isotope, which is beryllium-9. Does that mean that other than the normal beryllium, which has 4 protons and 4 neutrons and a mass number of 8, there is only one stable nuclide that isn't radioactive for beryllium? And what if beryllium-9 is called a stable isotope, what would the normal beryllium-8 with 4 protons and 4 neutons be called?

 

[tiny-tim]

hi marc32123! welcome to pf!

… beryllium has only one stable isotope, which is beryllium-9. Does that mean that other than the normal beryllium, which has 4 protons and 4 neutrons and a mass number of 8, there is only one stable nuclide that isn't radioactive for beryllium? And what if beryllium-9 is called a stable isotope, what would the normal beryllium-8 with 4 protons and 4 neutons be called?

miraculum?

from http://en.wikipedia.org/wiki/Monoisotopic_element …

The single mononuclidic exception is beryllium, which has 4 protons and 5 neutrons.
This isotope is prevented from having equal numbers of neutrons and protons (4 of each) by the instability toward double-alpha decay, which is favored due to the extremely tight binding of helium-4 nuclei.
It is prevented from having a stable isotope with 4 protons and 6 neutrons by the very large mismatch in proton/neutron ratio for such a light element. (Nevertheless, beryllium-10 has a half-life of 1.36 million years, which is too short to be primordial, but still indicates unusual stability for a light isotope with such an imbalance).​

 

[marc32123]

Thanks but still I am wondering, if beryllium-9 is called a stable isotope of beryllium, what would the normal beryllium-8 with 4 protons and 4 neutons be called?

 

[tiny-tim]

… what would the normal beryllium-8 with 4 protons and 4 neutons be called?

that's a rather strange use of the word "normal"!

it would only be a resonance, but i suppose you could call it "bihelium", since it is essentially an unstable combination of two helium nuclei (ie two alpha-particles) …

each helium nucleus exists in its own tightly-bound little world, pretty much oblivious of the other helium nucleus!

 

[jtbell]

what would the normal beryllium-8 with 4 protons and 4 neutons be called?

⁸Be undergoes alpha decay with a half-life of about 7 x 10^-17 s. I would call that "highly unstable."

http://en.wikipedia.org/wiki/Isotopes_of_beryllium

(what other kind of ⁸Be is there? )