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Introduction
Introduction
Lattice enthalpy value depends on two (2) important things: charge and size of the ion. If the charge is higher, a molecule will have a stronger lattice enthalpy. If the ion is smaller, a molecule will also have a stronger lattice enthalpy.
These rules can be applied by looking at the lattice enthalpy values. There are two (2) ways to calculate these values: theoretical and experimental. The experimental lattice enthalpy is calculated using the Born-Haber Energy Cycle, which is based on Hess’s Law. The theoretical lattice enthalpy is calculated from the ionic model which assumes that the crystal is made up of perfect, spherical ions and only interacts due to electrostatic forces.
Furthermore, we can see that the values of lattice enthalpy slightly differ from both theoretical and experimental as seen from the table below.
Excerpt 1: Jones online video
From the table, NaF has the highest value. This is because the ionic radius of the fluorine is smaller than chlorine and bromine. Also, the values of experimental are larger than the theoretical values.
Research Question
Research Question
Seeing how different the values are made me wonder about the credibility and usefulness of models in chemistry. It also made me question the importance of having two different values. This leads me to my research question: Investigating the effects of ionic radii and charge difference in experimental and theoretical lattice enthalpy values.
Prediction
Prediction
1. The ionic radii difference increases between cation and anion, it will also increase the percent difference of the Born-Haber Cycle and Born-Landé formula in lattice enthalpy values.
2. The electronegativity between electrons decreases, the percent difference will also increase. As the electronegativity gets smaller, the compound becomes more covalent.
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