Spin, electron magnetic moment from

The increase of the total magnetic moment from USe to UTe is the result of the decrease of spin moment from 5f electrons due to the stronger hybridization effects between U atom and Te atom. 

The unpaired electron has the complication that it is not localized on a single point but, in general, is delocalized on the entire molecule. So, in every point of space where the molecular orbital (MO) containing the unpaired electron has a non-zero value, the average electron magnetic moment sensed by the nucleus is different from zero and is proportional to (Sz) times the fraction of unpaired electron present at that point. Such a fraction is called spin density p, which for a single electron is given by the square of its wavefunction at that point. 

Calculate the spin-only magnetic moment for the following atoms and ions. (Remember the order of loss of electrons from transition metals described near the end of Section 2-2-4.)... 

The other lanthanides ions do not obey this simple relationship. The 4/electrons are well shielded from the entemal field by the overlying 5s and 5p electrons. Thus, the magnetic effect of the motion of the electron in its orbital is not quenched out. Thus, the magnetic moment must be calculated taking into account both the magnetic moment from the unpaired electron spins and that from the orbital motion. In lanthanides the spin contribution S and orbital contribution L couple together to give a new quantum number J. 

The coupling of the unpaired electrons with the nucleus being observed generally results in a shift in resonance frequency that is referred to as a hyperfine isotropic or simply isotropic shift. This shift is usually dissected into two principal components. One, the hyperfine contact, Fermi contact or contact shift derives from a transfer of spin density from the unpaired electrons to the nucleus being observed. The other, the dipolar or pseudocontact shift, derives from a classical dipole-dipole interaction between the electron magnetic moment and the nuclear magnetic moment and is geometry dependent. 

The spin-spin contact and dipolar terms arise from the interaction between the electronic magnetic moment and the internal magnetic field generated by the other electron at the position of the first electron... 

The magnetic moment of an atom is due entirely to partially filled subshells and unpaired spins. The completed subshells do not contribute to the permanent magnetic moment of an atom. In this connection we might remark that most molecules have an even number of electrons whose spins in the ground state are all paired. Also the subshells are usually complete so that there is no contribution to the magnetic moment from the orbital motion. It is unusual for a molecule to have a permanent magnetic moment the possession of a permanent magnetic moment is an important key to the electronic structure of the molecule. 

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