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Transition Metals 23 and Coordination Chemistry Visualizing Concepts 23.1 Analyze/Plan. Given the diagram of a trend moving across the fourth period of the chart, decide which atomic property the trend represents. Solve. Periodic properties are explained in terms of effective nuclear charge, Zeff. Moving from left to right in a period, Zeff increases because the increase in Z is not offset by a significant increase in shielding. Increasing Zeff leads to increasing ionization energy and electronegativity, but decreasing atomic radius. The chart shows a general decrease in magnitude of the property from K to Ge, so the property must be atomic radius. 23.2 Analyze. Given the formula of a coordination compound, determine the coordination geometry, coordination number, and oxidation state of the metal. Plan. From the formula, determine the identity of the ligands and the number of coordination sites they occupy. From the total coordination number, decide on a likely geometry. Use ligand and overall complex charges to calculate the oxidation number of the metal. Solve. (a) The ligands are one coordination site each, and en, ethylenediamine, two coordination sites, for a coordination number of 4. This coordination number has two possible geometries, tetrahedral and square planar. Pt is one of the metals known to adopt square planar geometry when CN = 4. N Pt N (b) CN = 4, coordination geometry = square planar (c) Pt(en)Cl₂ is a neutral compound, the en ligand is neutral, and the ligands are each -1, so the oxidation state of Pt must be +2, Pt(II). 23.3 Analyze. Given a ball-and-stick figure of a ligand, write the Lewis structure and answer questions about the ligand. Plan. Assume that each atom in the Lewis structure obeys the octet rule. Complete each octet with unshared electron pairs or multiple bonds, depending on the bond angles in the ball-and-stick model. Black = C, blue = N, red = gray = H. 692