CHAPTER23CHEM - Chapter 23: The Transition Elements and...

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Chapter 23: The Transition Elements and Their Coordination Compounds 23.1 Properties of the Transition Elements: Main group elements in each period change from metal to nonmetal, but all transition elements are metals. Most main group ionic compounds are colorless and diamagnetic, but many transition metal compounds are highly colored and paramagnetic. Electron Configurations of the transition metals and their ions: Condensed ground state e- configuration for the elements in d-block (transition elements) is: [noble gas] ns 2 (n – 1)d x , w/ n= 4 to 7 and x = 1 to 10 In periods 6 and 7, the condensed configuration includes the f -sublevel: [noble gas] ns 2 (n – 2)f 14 (n – 1)d x , w/ n = 6 or 7 and x = 1to 10. The partial (valence-level) e-configuration for the d-block elements excludes the noble gas core and the filled inner f sublevel: ns 2 (n – 1)d x , w/ n= 4 to 7 and x = 1 to 10 Exception: Cr [Ar]4s 1 3d 5 , Cu [Ar]4s 1 3d 10 (only one e- in 4s-block, other e- used to fill all of 3d-block) Atomic and Physical Properties of the transition elements: period across; group down Trends across a period PERIOD 4: 1. Atomic size: decreases overall across a period (decrease to the left). But there is a smooth, steady decrease across the main group elements (b/c e- are added to outer orbitals, which shield the increasing nuclear charge poorly) while in the transition elements atomic size decreases at first but then remains fairly constant (same size) b/c d-electrons fill inner orbitals so they shield outer e- from the increasing nuclear charge very efficiently. So, the outer 4s e- are not pulled closer. 2. Electronegativity: usually increases across a period (to the right towards F), but transition elements show small change in E.N., consistent w/ the small change in size. Main group shows steady, steep increase, while transition elements all have intermediate electronegative values. 3. Ionization energy: ionization of main group steeply increases from left to right, as e- become more difficult to remove from poorly shielded, increasing nuclear charge. In transition metals, the first ionization energies increase relatively little b/c the inner 3d e- shield effectively so 4s e- experiences only a slightly higher effective nuclear charge. Trends w/in a group: 1. Atomic size : as usual, atomic size increases from period 4 to 5 (down), same as for main-group, but there is no increase from Period 5 to 6 (both are about same size). Lanthanides (w/the f-sublevel) appear btw the 4d and 5d level, so element in period 6 is separated from the one above it in period 5 by 32 elements (ten 4d, six 5p, two 6s, and fourteen 4f orbitals) instead of just 18. The extra shrinkage that results from the increase in nuclear charge due to the addition of 14 protons is called lanthanide contraction . This decrease is about equal to the normal increase btw periods, so period 5 and 6 transition elements are about the same atomic sizes. 2.
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This note was uploaded on 11/14/2010 for the course CHEM 1A taught by Professor Okamura during the Fall '08 term at UC Riverside.

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CHAPTER23CHEM - Chapter 23: The Transition Elements and...

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