Polarizability large radii

Soft species easy to oxidize (bases) or reduce (acids) high polarizability large radii small differences in electronegativities between the acceptor and donor atoms low charge densities at acceptor and donor sites often have low-lying empty orbitals (bases) often have a number of d electrons (acids). 

A soft Lewis acid has a relatively high polarizability. Large atoms and low oxidation states often convey softness. Contrast with Hg , a typical soft acid. The ionic radius of Hg is 116 pm, almost twice the size of... 

The hydride ion is large, with a radius of 154 pm (1), falling between the fluoride and chloride ions. The large radius of the ion and its low charge make it highly polarizable and contribute to covalent character in... 

Phosphonium-based ILs are highly basic [118], having the generic formula [PRjR j X, where both R and R are alkyl groups, and X is a halide. Large radius and polarizable lone pair of electrons make them more nucleophilic. Phosphonium-based materials are one of the most thermally stable commercial ILs. Ultra-low vapor pressure and relatively high viscosity index make phosphonium-based ILs particularly attractive for high-temperature applications. 

Although we have illustrated the effects of polarizability of ions by considering a few cases where the effects are large, there must be some polarization effect for any combination of ions. However, there is an even more important consideration. It is known that the apparent radius of a given ion depends somewhat on the environment of the ion. For example, an ion surrounded by four nearest neighbors will appear to be slightly different in size from one that is surrounded by six ions of opposite charge. We have treated the ionic radius as if it were a fixed number that is the same in any type of... 

Soft Low-charge density Large ionic radius Easily excited outer shell electrons Cu+ High polarizability Low electronegativity Low-energy vacant orbitals Easily oxidized RSH, RS-, CN", CO... 

The hydride ion provides however a notable exception. This is not due to faults in the calculation, for a full variation-calculation (33) gives for the polarizeability a = 30 cm /naole while crystal data (34) lead to the much smaller value 3 cm /mole — a contraction of the electron-cloud radius by a factor of ]/10 1.8. An unusually large effect would of... 

A practical way of describing the environment is to consider the DNA molecule to be placed inside a cavity. Physically, the cavity is due to the sugar-phosphate backbone and the hydrophobicity of the DNA bases. Its characteristic size R is determined by the radius of the helix k 10 A. The space outside the cavity is filled with water, with dielectric constant 78 at room temperature, in which counterions are dissolved with equilibrium densities (far from the DNA molecule) Na= ci- Neglecting the polarizability of the backbone and the bases, we assume the cavity to be empty. It is readily shown that, because of the large dielectric constant of water, the interaction with the ions may be neglected [64]. 

The stability will once more increase with increasing charge and decreasing radius of the ion. A large moment or a large polarizability will favour the stability, provided on the other hand the shortest distance r remains small or at any rate the dipole is situated eccentrically. 

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