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Explain crystal structure of sodium chloride (NaCl). |
Answer» Solution :CRYSTAL STRUCTURE of sodium chloride (NaCl) (rock salt) :  The crystal LATTICE structure of NaCl is in three steps. This process is exothermic reaction. (i) Ionization enthalpy `(Delta_(i)H)` : `Na_((g)) rarr Na_((g))^(+) + e^(-) ...Delta_(i) H = 495.8 kJ mol^(-1)` (ii) Electron gain enthalpy `(Delta_(eg)H)` : `(Cl_((g)) + e^(-) rarr Cl_((g))^(-) ... Delta_(eg) H = - 348.7 kJ "mol"^(-1))/(because "(i) + (ii) enthalphy= 147.1 kJ mol"^(-1))` The sum of the two step is endothermic means energy is REQUIRED. (iii) Lattice enthalpy `(Delta_(L)H)`: `Na_((g))^(+) + Cl_((g))^(-) rarr NaCl_(s) .... Delta_(L) H = - 788 kJ " mol"^(-1)` `therefore` (i) + (ii) + (iii) enthalpy = - 640.9 kJ `"mol"^(-1)` Therefore, the energy released in the process is more than the energy absorbed in formation of NaCl. |
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