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Grade: 12th pass

                        

How can we calculate the elecroneatiity of Zno by followiny Pouling principle in electron volts(ev).

4 years ago

Answers : (1)

dolly bhatia
54 Points
							
Pauling Electronegativity:
Linus Pauling was the original scientist to describe phenomena of electronegativity. Best way to describe his method is to look at a hypothetical molecule (XY). By comparing measured X-Y bond energy with theoretical X-Y bond energy (computed as average of the X-X bond energy and Y-Y bond energy), we can describe affinities of these two atoms with respect to each other.
Δ Bond Energies = (X-Y)measured – (X-Y)expected
If electronegativities of X and Y are the same, then one could expect measured bond energy to equal theoretical (expected) bond energy and therefore the delta bond energies would be zero. If electronegativities of these atoms are not the same, one could see a polar molecule where one atom would start to pull electron density toward itself, causing it to become partially negative. 
By doing careful experiments and calculations, Pauling came up with a slightly sophisticated equation for relative electronegativities of two atoms in a molecule: EN(X)-EN(Y) = 0.102 (Δ1/2). In this equation, factor 0.102 is a conversion factor between kJ and eV to keep units consistent with bond energies.
By assigning value of 4.0 to Fluorine(most electronegative element), Pauling set up relative values for all elements. This was when he first noticed the trend that electronegativity tended to increase as one moved left to right and bottom to top along periodic table. Range of values for Pauling’s scale of electronegativity ranges from fluorine to francium (least electronegative = 0.7). furthermore, if electronegativity difference between two atoms is very large, then bond type tends to be more ionic, however, if difference in electronegativity is small, then it is a nonpolar covalent bond.
Absolute electronegativity (or electron affinity) is surface-independent but its exact determination is difficult due to spontaneous along c-axis in ZnO. ZnO has been used by mankind since smelting of brass and its semiconductor properties have been under investigation. ZnO is distinct from many other semiconductors from II-VI group, named for groups from periodic table that individual compounds are found, because of large electronegativity between the two atoms. Bond between oxygen, a highly electronegative element and zinc, an atom with very low electronegativity, has such uneven electron distribution between the atoms that individual elements can be treated as ions. This results in unique crystal structure when compared to other group II-VI semiconductors. Bonds in ZnO are oriented in a tetrahedral geometry and the two crystal structures associated with this geometry are zinc-blende and wurtzite. While other group II-VI semiconductors tend to organize themselves in zinc-blende structure, polarity in ZnO bonds predisposes compound into crystallizing in wurtzite type structure. Wurtzite type structure lacks inversion symmetry – there is no space in where atoms can be reflected through one point and have resulting structure to be identical to one before symmetry operation – which results in compounds with this structure behaving piezoelectrically. This happens because when stress is applied at apex of tetrahedrally coordinated Zn^+2 and O^-2 ions , centers of cations and anions are displaced , inducing a dipole moment. This is repeated along cells in crystal and causes macroscopic potential (piezopotential) drop along strain direction.
4 years ago
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