Question: out of Cao ,MgO ,BeO ,SrO which compound is the strongest ?...

Question

out of Cao ,MgO ,BeO ,SrO which compound is the strongest ?

Answer 1

Solution

The strength of an ionic compound is primarily determined by its lattice energy. A higher lattice energy indicates a stronger ionic bond and a more stable compound.

Lattice energy ( $U$ ) is directly proportional to the product of the charges of the ions ( $q_1 q_2$ ) and inversely proportional to the internuclear distance ( $r_0$ , which is the sum of the ionic radii):

U \propto \frac{q_1 q_2}{r_0}

In the given compounds (CaO, MgO, BeO, SrO), the anion is oxide (O²⁻), and the cations are Be²⁺, Mg²⁺, Ca²⁺, and Sr²⁺. All cations have a charge of +2, and the anion has a charge of -2. Therefore, the product of charges $q_1 q_2$ is constant for all these compounds.

Thus, the lattice energy primarily depends on the internuclear distance $r_0$ . Since $r_0 = r_{cation} + r_{anion}$ and $r_{anion}$ (radius of O²⁻) is constant, the lattice energy is inversely proportional to the size of the cation:

U \propto \frac{1}{r_{cation}}

The cations Be²⁺, Mg²⁺, Ca²⁺, and Sr²⁺ belong to Group 2 of the periodic table. As we move down a group, the ionic radius increases due to the addition of new electron shells.

The order of increasing ionic radii for these cations is:

Be²⁺ < Mg²⁺ < Ca²⁺ < Sr²⁺

Since lattice energy is inversely proportional to the ionic radius of the cation, the compound with the smallest cation will have the highest lattice energy and thus be the strongest. Be²⁺ is the smallest cation among the given options. Therefore, BeO will have the highest lattice energy and be the strongest compound.

The order of lattice energy is:

BeO > MgO > CaO > SrO

The strongest compound is BeO.