Based on coulomb's law of electrostatic attraction of oppositely-charged species, which of the following chlorine-containing compounds would be predicted to have the greatest (most exothermic) lattice energy? cacl2 nacl mgcl2 kcl ccl4

Based on Coulomb's Law of electrostatic attraction of oppositely-charged species, the chlorine-containing compound that is predicted to have the greatest (most exothermic) lattice energy is; MgCl₂

     The lattice energy is defined as the energy required to dissociate one mole of an ionic compound to its constituent gaseous ions.

       Thus; F =  (q₁  ×  q ₂)/r²

        Now, Lattice energy is inversely proportional to the size of the ions. This implies that as the size of the ions increases, then the lattice energy will decrease. The size of the ions is also called the atomic radii.

Thus, as atomic radii increases, lattice energy will decrease.

      From the formula above and definition, we can tell that Lattice energy decreases down a group. Also, lattice energy will increase as the charges increase.

Now, the compounds we are dealing with are;

CaCl₂ - Calcium Chloride

NaCl - Sodium Chloride

MgCl₂ - Magnesium Chloride

KCl - Potassium Chloride

CCl₄ - Carbon tetrachloride

The charges of the metals that form the chlorides above are;

Ca = +2

Na = +1

Mg = +2  

K =  +1

The highest charges are Ca and Mg.

Now, they both belong to group two of the periodic table with Ca below Mg in the periodic table and as such Mg will have a greater Lattice energy.

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