Bonds unlike atoms

The simple Bragg-Williams treauiient of this behaviour assumes an unlike atom bond strengdi which is greater than the like atom bonding and calculates the entropy of mixing as a function of die disorder which counterbalances this negative heat of formation. The relationship between the Curie temperature, Tc, and the bond energies is... 

Polar bond A chemical bond that has positive and negative ends characteristic of all bonds between unlike atoms, 182-183... 

It is shown that the energy of a normal covalent bond A-B between unlike atoms is probably represented more closely by the geometric mean of the bond energies for A-A and B-B than by their arithmetic mean. 

In the above discussion the effect of difference in electronegativity of unlike atoms on bond length (usually a decrease) has been ignored. There is the possibility also of a small change in bond length between unlike atoms, such as of a metal and a metalloid, that reflects the difference in the nature of the overlapping orbitals, in addition to the effects of partial ionic character and of electron transfer. I believe that a thorough... 

Hydrogen bonds between unlike atoms, as in NH4F, would not lead to residual entropy. 

Unlike the geometries for other steric numbers, the five positions in a trigonal bipyramld are not all equivalent, as shown in Figure 9-21a. Three positions lie at the comers of an equilateral triangle around the phosphorus atom, separated by 120° bond angles. Atoms in the trigonal plane are In equatorial positions. The other two positions... 

Plastoquinone, whose line structure appears in the margin, has ten double bonds. Unlike the bonds in the tail of retinal, however, the bonds in the long tail of plastoquinone are not delocalized because s p -hybridized carbon atoms separate them. The delocalized 7t system of plastoquinone is its planar ring of six carbon atoms, with two of the carbon atoms double-bonded to outer oxygen atoms. 

In a covalent single bond between unlike atoms, the electron pair forming the a bond is never shared absolutely equally between the two atoms it tends to be attracted a little more towards the more electronegative atom of the two. Thus in an alkyl chloride (20), the... 

The zincblende (ZB), or sphalerite, structure is named after the mineral (Zn,Fe) S, and is related to the diamond structure in consisting entirely of tetrahedrally-bonded atoms. The sole difference is that, unlike diamond, the atoms each bond to four unlike atoms, with the result that the structure lacks an inversion center. This lack of an inversion center, also characteristic of the wurtzite structure (see below), means that the material may be piezoelectric, which can lead to spurious ringing in the free-induction decay (FID) when the electric fields from the rf coil excite mechanical resonances in the sample. (Such false signals can be identified by their strong temperature dependence due to thermal expansion effects, and by their lack of dependence on magnetic field strength). 

Bonding electrons are not shared equally between unlike atoms, which are bonded together because of the difference in the affinity of different... 

Pauling also suggested that the single bond length between two unlike atoms is approximately given by the arithmetic average of the two bonds <7ab = ( aa + <31bb)/2. 

The existence of many ionic structures in MCVB wave functions has often been criticized by some workers as being unphysical. This has been the case particularly when a covalent bond between like atoms is being represented. Nevertheless, we have seen in Chapter 2 that ionic structures contribute to electron delocalization in the H2 molecule and would be expected to do likewise in all cases. Later in this chapter we will see that they can also be interpreted as contributions from ionic states of the constituent atoms. When the bond is between unlike atoms, it is to be expected that ionic stmctures in the wave function will also contribute to various electric moments, the dipole moment being the simplest. The amounts of these ionic structures in the wave functions will be determined by a sort of balancing act in the variation principle between the diagonal effects of the ionic state energies and the off-diagonal effect of the delocalization. 

The gas in now mixed and recondensed. The P bonds are all reestablished but now each molecule has a number of neighbours consisting of A and B and not, as before, neighbours of the same kind. For every bond formed between two like atoms, an energy LAjP or Lb/P will be released, and for bonds between unlike atoms there will be a different value which we will call LABjP. 

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