Question

Rank the following compounds from largest to smallest according to their expected magnitude in lattice energy. Rank from largest to smallest lattice energy To rank items as equivalent, overlap them. Cs1 KI MgS KBr BeO Largest Lattice Energy Smallest Lattice Energy

Answer 1

Concepts and reason

The amount of energy is released when two gaseous ions bring together to form one mole of ionic solid is called as lattice energy.

Charges on the gaseous ions and their radius effects on the magnitude of the lattice energy.

Compare the ionic charges of the ions that present in the compounds and rank them.

Fundamentals

The mathematical expression for the lattice energy is as follows:

$U = - \frac{{{N_A}M{z^ + }{z^ - }{q_e}^2}}{{4\pi {\varepsilon _{\rm{o}}}{r_{\rm{o}}}}}\left( {1 - \frac{1}{n}} \right)$

Here, N_A is the Avogadro constant, M is the Madelung constant, z⁺ are z⁻ the charge number of cation and anion respectively; ${q_e}$is the elementary charge, ε₀ is the permittivity, r₀ is the distance to closest ion, and n is the Born exponent.

The molecule ${\rm{BeO}}$has ${\rm{B}}{{\rm{e}}^{2 + }}$and${{\rm{O}}^{2 - }}$ions; charges on them are +2 and -2 respectively.

The molecule ${\rm{MgS}}$has ${\rm{M}}{{\rm{g}}^{{\rm{2 + }}}}$and${{\rm{S}}^{2 - }}$ions; charges on them are +2 and -2 respectively.

The molecule ${\rm{CsI}}$has ${\rm{C}}{{\rm{s}}^ + }$and${{\rm{I}}^ - }$ions; charges on them are +1 and -1 respectively.

The molecule ${\rm{KI}}$has ${{\rm{K}}^ + }$and${{\rm{I}}^ - }$ions; charges on them are +1 and -1 respectively.

The molecule ${\rm{KBr}}$has ${{\rm{K}}^ + }$and${\rm{B}}{{\rm{r}}^ - }$ions; charges on them are +1 and -1 respectively.

The expected magnitude in lattice energy of the molecules is as follows:

${\rm{BeO > MgS > KBr > KI > CsI}}$

Order of lattice energy of the molecules form largest to smallest is as follows:

${\rm{BeO > MgS > KBr > KI > CsI}}$

Ans:

Rank from largest to smallest lattice energy is as follows:

${\rm{BeO > MgS > KBr > KI > CsI}}$