Yb (s) + 3 I2 (g) → 2 YbI3 (s) [white] The ytterbium(III) ion absorbs light in the near infrared range of wavelengths, but not in visible light, so ytterbia, Yb2O3, is white in color and the salts of ytterbium are also colorless. Ytterbium dissolves readily in dilute sulfuric acid to form solutions that contain the colorless Yb(III) ions, which exist as nonahydrate complexes: 2 Yb (s) + 3 H2SO4 (aq) + 18 (l) → 2 [Yb(H2O)9]3+ (aq) + 3 (aq) + 3 H2 (g) Yb(II) vs. Yb(III) Although usually trivalent, ytterbium readily forms divalent compounds. This behavior is unusual for lanthanides, which almost exclusively form compounds with an oxidation state of +3. The +2 state has a valence electron configuration of 4f14 because the fully filled f-shell gives more stability. The yellow-green ytterbium(II) ion is a very strong reducing agent and decomposes water, releasing hydrogen gas, and thus only the colorless ytterbium(III) ion occurs in aqueous solution. Samarium and thulium also behave this way in the +2 state, but europium(II) is stable in aqueous solution. Ytterbium metal behaves similarly to europium metal and the alkaline earth metals, dissolving in ammonia to form blue electride salts. Isotopes Natural ytterbium is composed of seven stable isotopes: 168Yb, 170Yb, 171Yb, 172Yb, 173Yb, 174Yb, and 176Yb, with 174Yb being the most common, at 31.8% of the natural abundance). 27 radioisotopes have been observed, with the most stable ones being 169Yb with a half-life of 32.0 days, 175Yb with a half-life of 4.18 days, and 166Yb with a half-life of 56.7 hours. All of the remaining radioactive isotopes have half-lives that are less than two hours, and most of these have half-lives under 20 minutes. Ytterbium also has 12 meta states, with the most stable being 169mYb (t1/2 46 seconds). The isotopes of ytterbium range in atomic weight from 147.9674 atomic mass unit (u) for 148Yb to 180.9562 u for 181Yb. The primary decay mode of ytterbium isotopes lighter than the most abundant stable isotope, 174Yb, is electron capture, and the primary decay mode for those heavier than 174Yb is beta decay. The primary decay products of ytterbium isotopes lighter than 174Yb are thulium isotopes, and the primary decay products of ytterbium isotopes with heavier than 174Yb are lutetium isotopes. Occurrence Ytterbium is found with other rare-earth elements in several rare minerals. It is most often recovered commercially from monazite sand (0.03% ytterbium). The