Question:

$CaO$ and $NaCl$ have the same crystal structure and approximately the same ionic radii. If $U$ is the lattice energy of $NaCl$, the approximate lattice energy of $CaO$ is

Updated On: Jul 28, 2022
  • U/2
  • U
  • 2U
  • 4U
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The Correct Option is D

Solution and Explanation

Lattice energy $=-\frac{q_{1}q_{2}}{r^{2}}$ where $q_1$ and $q_2$ are charges on ions and r is the distance between them. Since interionic distances in CaO and NaCl are similar, (larger cation has smaller anion and vice versa) therefore, r is almost the same. Therefore, lattice energy depends only on charge. Since the magnitude of charge on $Na^+$ and $Cl^-$ ions is unity and that on $Ca^{2+}$ and $O^{2-}$ ions is 2 each, therefore, the lattice energy of CaO is four times the lattice energy of NaCl, i.e.,4U.
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Concepts Used:

Chemical Bonding and Molecular Structure

Such a group of atoms is called a molecule. Obviously, there must be some force that holds these constituent atoms together in the molecules. The attractive force which holds various constituents (atoms, ions, etc.) together in different chemical species is called a chemical bond.

Types of Chemical Bonds:

There are 4 types of chemical bonds which are formed by atoms or molecules to yield compounds. 

  • Ionic Bonds - Ionic bonding is a type of chemical bonding which involves a transfer of electrons from one atom or molecule to another.
  • Covalent Bonds - Compounds that contain carbon commonly exhibit this type of chemical bonding. 
  • Hydrogen Bonds -  It is a type of polar covalent bonding between oxygen and hydrogen wherein the hydrogen develops a partial positive charge
  • Polar Bonds - In Polar Covalent chemical bonding, electrons are shared unequally since the more electronegative atom pulls the electron pair closer to itself and away from the less electronegative atom.

Factors Affecting Bond Enthalpy in Chemical Bonding:

  • Size of the Atom
  • Multiplicity of Bonds
  • Number of Lone Pair of Electrons Present
  • Bond Angle