Question

Periclase, crystalline Mgo, has the same unit cell as NaCl. In this unit cell the Mg2+ ions occupy all of the face-centered positions and 02-ions occupy all of the octahedral holes. Periclase has an edge length of 4.212 Å. A representation of the unit cell is shown below. Magnesium ions have a radius of 0.89 Å. Determine the ionic radius, in A, of 02-ions in periclase. 02- Mg2+

Answer 1

MX Z crystaine Mgo is Fcc (face center cubic) i emg2+ ions occupy au of face-center possition and o2-ions occupy au of the octahydral hores. For F.C.C per unit celu atoms (2)=4 Density of solid (ngo) is calculated by M= molar mass of ngo NX a3 2= No. of atoms per unit cell Mosar mass of mgo (24-116) = 40 g/mol eube. Avogadro number, NA= 6.023x10² unit cen (Z) = 4 edge length of cube (aj = 4.212 A = 4.212x 10 cm N = Avogadro number a=redge-length of 23 No. of atoms pen --8 Чох ч D 6:023x1023 x (4.212 x 1083 160 45 D = 3.55 g/cm3 Density of peniciase is 3.55 g/cm3

Lattice energy of naci is - 787.2 KI/mae fe -U. E-A= ejeefron affinity of U2, OH-348.6 KI) more Born-Heben cycle of Nach enstali -Na (s) ts Na (4) + I.? Na Laj- -cl2 (g) + 2 Dg ILG) EA, coca. - AHS Nach(s)k According to Hesse's Law - +OHF = +S+ I.P+{ D + £.A+U where, Otf = He at of formation of wac, OH = -411-28/mor = subumation energy of wa, H = 107.5 KJ/more Jp = jonisation potential of na, SH° = 495.8kJ/more D - Dissociation energy of c12.0H° = 242.6 kJ/moe S put this values of above equation and we get -418:2 = 107.5 + 495.8+ { (242.0)-348.6+U -u= 411.2 + 376 U = -787.2 KJ/mne