Question

Bromine consists of two isotopes with masses of $ 78.92 $ and $ 80.92 $ amu. What is the abundance of these two isotopes?

Answer 1

Hint: Bromine is a chemical element with the symbol $ Br $ and atomic number $ 35 $ . It is the third-lightest halogen, and is a fuming red-brown liquid at room temperature that evaporates readily to form a similarly colored vapor. Elemental bromine is very reactive and thus does not occur free in nature, but in colorless soluble crystalline mineral halide salts, analogous to table salt.

Complete Step By Step Answer:
Bromine has two stable isotopes, $ ^{79}Br $ and $ ^{81}Br $ . These are its only two natural isotopes, with $ ^{79}Br $ making up $ 51\% $ of natural bromine and $ ^{81}Br $ making up the remaining $ 49\% $ Both have nuclear spin $ \dfrac{3}{2} - $ and thus may be used for nuclear magnetic resonance, although $ ^{81}Br $ is more favorable. The relatively $ 1:1 $ distribution of the two isotopes in nature is helpful in identification of bromine-containing compounds using mass spectroscopy. Other bromine isotopes are all radioactive, with half-lives too short to occur in nature. Of these, the most important are $ ^{80}Br $ ( $ {t_{\dfrac{1}{2}}} = 17.1 $ min), $ ^{80m}Br $ ( $ {t_{\dfrac{1}{2}}} = 4.421 $ h), and $ ^{82}Br $ ( $ {t_{\dfrac{1}{2}}} = 35.28h $ ), which may be produced from the neutron activation of natural bromine. The most stable bromine radioisotope is $ ^{77}Br $ ( $ {t_{\dfrac{1}{2}}} = 57.04 $ h) $ ^{79}Br $ and $ ^{81}Br $ , having relative mass abundances of $ 50.686\% $ and $ 49.314\% $ , respectively (Eggenkamp and Coleman, 2000). Variations in isotopic composition are reported as $ {\delta ^{81}}Br $ (SMOB), where SMOB is standard mean oceanic bromide.

Note:
The primary decay mode of isotopes lighter than $ ^{79}Br $ is electron capture to isotopes of selenium; that of isotopes heavier than $ ^{81}Br $ is beta decay to isotopes of krypton; and $ ^{80}Br $ may decay by either mode to stable $ ^{80}Sr $ or $ ^{80}Kr $ .