Among the following compounds, the number of compounds having greater magnitude of lattice energy than RbBr, are
NaCl, KF, RbCl, CsBr, NaBr, KCl, CsI, RbI.
Lattice energy depends on ion charges and sizes. Higher charge and smaller ions increase lattice energy. RbBr has large Rb⁺ and Br⁻ ions, so low lattice energy.
Compounds with smaller ions (NaCl, NaBr, KF, KCl) or higher charge (none here) have greater lattice energy. RbCl, CsBr, CsI, RbI have larger ions, so lower lattice energy.
Comparing: NaCl (small Na⁺), NaBr (small Na⁺), KF (small F⁻), KCl (smaller than RbBr) have greater lattice energy. Others have larger ions.
Final Answer: 4
Lattice energy is the energy released when gaseous ions combine to form one mole of a solid ionic compound. It depends primarily on two factors:
All compounds given (NaCl, KF, RbCl, CsBr, NaBr, KCl, CsI, RbI) have +1 and -1 ion charges like RbBr, so we only need to compare ionic sizes.
Step 1: Identify RbBr's ion sizes - Rb⁺ (152 pm) and Br⁻ (196 pm)
Step 2: For each compound, calculate the sum of cation and anion radii. Smaller sum means higher lattice energy than RbBr.
Step 3: Compare each compound:
Final Answer: 5 compounds have greater lattice energy than RbBr: NaCl, KF, RbCl, NaBr, and KCl.
Lattice Energy (Born-Landé equation):
Where N is Avogadro's number, M is Madelung constant, e is electron charge, ε₀ is permittivity of free space, r₀ is distance between ions, and n is Born exponent.