Transition Elements Atomic Structure and Properties

The square ot the radial part of th(e wavefunction of an orbital provides information about how tho electron density within the orbital varies as a function of distance from the nucleus. These radial distribution functions show that, in a given principle shell, the maximum electron density is reached nearer to the nucleus as the quantum number I increases. However, the proportion of the total electron density which is near to the nucleus is larger for an electron in an s orbital than in a p orbital. 

Lanthanides Element Valence shelP Ionic radius (pm) M3 Actinides Element Valence shell Ionic radius (pm) M3 M  

Because, in transition metal ions, the energy of the 3d subshell lies below that of the 4s subshell, the remaining valence shell electrons in 3d-block metal ions occupy the 3d rather than the 4s subshell. The second- and third-row d-block elements show similar general trends of 

Quantum mechanics shows that if electrons in different orbitals have parallel spins (t, t) they occupy a larger volume of space than if they have antiparallel spins (t, i). Intuitively this would suggest that the electron-electron repulsion will be smaller in the system with parallel spins than in that with antiparallel spins. In fact such systems do show an additional stability due to an exchange energy, , This is, in elTect. an expression of Hund s rule. 

Hund s rule stator that the lowest energy, or ground, state ia an atom or ion will be that witti ttie highest spin multiplioiy Tlial IS the state with the most unpaired cHectrons. As an C xam[ i , thc energy of an atom or 11)11 wiiii Itiroo luter electrons will bo lower wtion they havi-parallel spins iT, T, T). m a spin triplet, than when one pair of ti ie electrons ha.s antiparallel spins 1.4. i ). in a spin doublet. 

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