We can define average bond enthalpies and bond lengths for ionic bonds, just like we have for covalent bonds. Which ionic bond is predicted to have the smaller bond enthalpy, Li—F or Cs—F?

Verified step by step guidance

1. Step 1: Understand the concept of bond enthalpy. Bond enthalpy is the energy required to break one mole of a bond in a gaseous substance. For ionic bonds, it is influenced by the charges on the ions and the distance between them.
2. Step 2: Consider the factors affecting bond enthalpy in ionic compounds. The bond enthalpy is generally higher for ions with higher charges and smaller ionic radii, as these factors increase the electrostatic attraction between the ions.
3. Step 3: Compare the ionic radii of Li+ and Cs+. Lithium (Li) is in the second period of the periodic table, while cesium (Cs) is in the sixth period. This means that Li+ has a smaller ionic radius compared to Cs+.
4. Step 4: Analyze the effect of ionic radii on bond enthalpy. A smaller ionic radius (Li+) results in a shorter bond length and stronger electrostatic attraction compared to a larger ionic radius (Cs+), leading to a higher bond enthalpy.
5. Step 5: Conclude which bond has the smaller bond enthalpy. Since Cs+ has a larger ionic radius than Li+, the Cs—F bond is predicted to have a smaller bond enthalpy compared to the Li—F bond.

Key Concepts

Ionic Bonding

Ionic bonding occurs when electrons are transferred from one atom to another, resulting in the formation of charged ions. The electrostatic attraction between these oppositely charged ions creates a strong bond. The strength of ionic bonds is influenced by the charges of the ions and the distance between them, which is critical for understanding bond enthalpy.

Bond Enthalpy

Bond enthalpy, or bond dissociation energy, is the amount of energy required to break a bond in a molecule in the gas phase. It is a measure of bond strength; higher bond enthalpies indicate stronger bonds. In ionic compounds, bond enthalpy can vary significantly based on the size and charge of the ions involved, affecting the stability of the ionic bond.

Trends in Ionic Radii

Ionic radii refer to the size of ions in a crystal lattice. As you move down a group in the periodic table, ionic radii increase due to the addition of electron shells. This increase in size affects bond length and bond enthalpy; larger ions typically form longer and weaker bonds, which is essential for predicting the bond enthalpy of Li—F versus Cs—F.