Radioactive isotopes group 17 elements

Radon is the heaviest of the hehum-group elements and the heaviest of the normal gaseous elements. It is strongly radioactive. The most common isotope, Rn, has a half-life of 3.825 days (49). Radon s scarcity and radioactivity have severely limited the examination of its physical properties, and the values given ki Table 3 are much more uncertain than are the values Hsted for the other elements. 

Symbol Co atomic number 27 atomic weight 58.933 a transtion metal, Group VIll (Group 9) element electron configuration [Ar]3d 4s2 valence +2 and +3 also valences 0, +1, +4, and +5 are known natural isotopes Co-59 (99.8%) and Co-57 (0.2%) radioactive isotope Co-60. 

Symbol Ni atomic number 28 atomic weight 58.693 a transition metal element in the first triad of Group VIll(Group 10) after iron and cobalt electron configuration [Ar]3d 4s2 valence states 0, -i-l, +2, and -f-3 most common oxidation state +2 the standard electrode potential, NF+ -1- 2e Ni -0.237 V atomic radius 1.24A ionic radius (NF+) 0.70A five natural isotopes Ni-58 (68.08%), Ni-60 (26.22%), Ni-61 (1.14%), Ni-62 (3.63%), Ni-64 (0.93%) nineteen radioactive isotopes are known in the mass range 51-57, 59, 63, 65-74 the longest-lived radioisotope Ni-59 has a half-life 7.6x10 years. 

Symbol Rb atomic number 37 atomic weight 85.468 a Group I (Group 1) alkali metal element electron configuration [Kr] 5si valence -i-l atomic radius 2.43A ionic radius, Rb+ 1.48A atomic volume 55.9 cc/g-atom at 20°C ionization potential 4.177 V standard electrode potential Rb+ + e Rb, E° = -2.98V two naturally-occurring isotopes, Rb-85 (72.165%) and Rb-87 (27.835%) Rb-87 radioactive, a beta emitter with a half-bfe 4.88xl0i° year twenty-seven artificial radioactive isotopes in the mass range 74—84, 86, 88-102. 

Symbol Na atomic number 11 atomic weight 22.9898 a Group lA (Group 1) alkali metal element electron configuration [NejSs valence +1 atomic radius 1.85A ionic radius, Na" in crystals 1.02A (for a coordination number 6) ionization potential 5.139 eV standard electrode potential, E°(Na+ + e Na) -2.71 V one naturally-occurring stable isotope, Na-23 (100%) sixteen artificial radioactive isotopes in the mass range 19-22, 24—35 longest-lived radioisotope, Na-22, ti/2 2.605 year shortest-lived isotope Na-35, ti/2 1.5 ms. 

CHROMIUM. [CAS 7440-47-3[. Chemical element, symbol Cr. at. nil. 24. at. wi. 51.996, periodic table group 6. mp 1837- 1877°C. bp 2672 C, density 7.2 g/cm. Elemental chromium has a body-centered cubic crystal structure The metal is silver-white with a slight gray-blue tinge, very hard (9.0 on the Mohs scale), capable of taking a brilliant polish, not appreciably ductile or malleable. The element is not aflected by air or HyO al ordinary temperatures, but when heated above 200°C, chromic oxide CryOt is formed. There tire four stable isotopes f0Cr. and, Cr through wCr. Fuur radioactive isotopes have been identihed, all with comparatively short half-lives 4 Cr. Jl,Cr. 1 Cr. and 5Cr, The element was first identified by Vauquelin in 1797. 

---