Nucleus defined

A three-membered ring ihiist bn since three points (the three cerbon nuclei) define a plane. A fpi)i ftt Mled ring need not be planar, but pudteriqg... 

The continuous electron density plus the discrete set of nuclei define the total charge density D(r) of a molecular system. The electrostatic potential U(r) [50-52] is related to D(r) through Poisson s equation ... 

In molecular orbital theory the product v oy is again replaced by q>iElectron transfer from ft to q>f results in a shift in charge density in the molecule. Electron density increases in the regions where q>i and positive overlap) and decreases where they have opposite signs (negative overlap). The positively charged nuclei then move in the direction of increased electron density. The motion of the nuclei defines a reaction coordinate. The symmetry of Q is the same as that of the product Pi X q>f. 

The configuration of the nuclei of the total system can be defined by a set of coordinates given by vector R. We divide the whole system into the interacting subsystems ( molecules ) A, B,C,... with their intemal geometries (configurations of the nuclei) defined by Ra, Rfi, Rc, and the fixed numbers of electrons Na, Nb,, Nc, , respectively. The rest of the coordinates ( external ) that determine the intermolecular distances and the orientations of the molecules in a global coordinate system will be denoted as R j ... 

The first thing to note about Fig. 3.1 is that the two hydrogen nuclei define an internuclear axis, which is conventionally labelled z the x and y axes remain undefined, but the xy plane can be - with care. In principle, either the center of nuclear mass or the center of nuclear charge can be chosen to serve as the origin of our coordinate system. When both Hj and are protons, either criterion fixes the origin at i, the point midway between them. However, when is a... 

A stable nucleus remains intact indefinitely, but the great majority of nuclei are unstable. An unstable nucleus exhibits radioactivity, emission of radiation due to its spontaneous disintegration. In Section 23.2, you ll see that each type of unstable nucleus has its own characteristic rate of radioactive decay. In this section, we cover important terms and notation for nuclei, define the types of emission, and desalbe various modes of radioactive decay and how to predict which occurs for a given nucleus in the process, you ll learn how to write nuclear equations. 

The average distance between the electron and their nuclei (defined by the stationary state)... 

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