18 e Rule for Transition Elements Remember the dot structure for CO? -1 +1 C∷O:> :C≡O:> ∷C=O: Consider Cr,a transition element: Chromium:[Ar](4s)2(3d)4-6 valence e Like most transition elements,Cr needs 18 e in its shell. O 12 e from CO's +6 e from Cr =18 total e;formula is Cr(CO)e Dot structures can predict C≡O: molecules;if we are given :O蕊C8 an exception,we can explain its existence,and figure out some of its chemical properties. 4Cr 18 e- Rule for Transition Elements • Remember the dot structure for CO? C O C O • Consider Cr, a transition element: Chromium: [Ar] (4s)2 (3d)4 → 6 valence e- • Like most transition elements, Cr needs 18 e- in its shell. O C C O C O C O 12 e- from COʼs + 6 e- from Cr = 18 total e- ; formula is Cr(CO)6 Dot structures can predict molecules; if we are given an exception, we can explain its existence, and figure out some of its chemical properties. C O -1 +1 XIV-4