Question

For a Na+-Cl- ion pair, attractive and repulsive energies, EA and ER respectively, depend on the distance between the ions r, according to:  

EA= -1.436/r   

ER= 7.32 X 10-6/ r8   

EN= EA + ER  

For the above expressions energy is expressed as electron-volt per Na+-Cl- ion pair, and r is the distance in nanometers.   

Plot EN, EA and ER versus r up-to 0.8 nm.   

On the basis of this plot, determine the equilibrium spacing ro between Na+ and Cl- ions, and the magnitude of the bond energy Eo between the two ions.   

Calculate the values of  Eo and ro and compare these values with those you got from the above plot.  

q2

Answer 1

r(in nm)	EA	ER	EN
0	?	?	?
0.1	-14.36	732	717.64
0.2	-7.18	2.859375	-4.320625
0.3	-4.7866667	0.111568358	-4.675098308
0.4	-3.59	0.011169434	-3.578830566
0.5	-2.872	0.00187392	-2.87012608
0.6	-2.3933333	0.000435814	-2.392897519
0.7	-2.0514286	0.000126977	-2.051301594
0.8	-1.795	4.36306E-05	-1.794956369

so, from graph, the equilibrium spacing ro between Na+ and Cl- ions = 0.3nm and the magnitude of the bond energy Eo between the two ions = -5eV per Na+-Cl- pair