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Lattice Enthalpy of an Ionic Solid - Understanding Lattice Structure and Enthalpy
IMPORTANT LINKS
The Solid State
Decoding Lattice Structure and Lattice Enthalpy
Ionic compounds are known for their robust molecular force of attraction, which is why they are typically found in solid states. In these ionic solids, the molecules form a three-dimensional grid-like pattern, commonly referred to as a lattice structure. The lattice enthalpy of an ionic solid is the energy needed to separate one mole of the solid ionic compound into gaseous ions entirely.
Lattice enthalpy serves as an indicator of the strength of an ionic compound. The formation of ions involves either the loss or gain of electrons, processes which either require or release energy respectively. Consequently, the strength of an ionic compound can be related to the ease of formation of positive and negative ions from their neutral atoms. This ease of formation is dependent on ionisation enthalpy and electron affinity, as explained below:
- The creation of positive ions necessitates the removal of electrons. The energy needed to remove an electron from an atom is known as ionisation enthalpy. Atoms with lower ionisation potential ( ionisation enthalpy ) will exhibit higher lattice energy.
- Negative ions are formed by the addition of an electron. Electron gain enthalpy refers to the energy released when an electron is added to an atom. Thus, the higher the electron affinity, the greater the lattice energy.
Factors Influencing Lattice Enthalpy1. Ion Charge:
The ions within the lattice crystal are drawn to each other due to the electrostatic force of attraction. This force is directly proportional to the charge magnitude, meaning the higher the charge, the stronger the lattice enthalpy. For instance, while Sodium Chloride and Magnesium Chloride share the same crystal lattice arrangement, the latter's lattice enthalpy is greater. This is due to the 2+ charge on magnesium ions compared to the 1+ charge on sodium ions, reinforcing the notion that electrostatic force of attraction is directly proportional to charge.
2. Atom Size:
Smaller atoms, due to their reduced interatomic distances, have stronger binding forces, leading to higher lattice enthalpy. For instance, as we move down group 17 of the modern periodic table from fluoride to bromide, the lattice energy continually decreases for their lithium salts, due to the increasing atom size from fluoride to bromide.
Dive deeper into lattice enthalpy, crystal lattices and the stability of ionic compounds.
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Frequently Asked Questions
What is a lattice structure?
In ionic solids, the molecules are arranged in a three-dimensional grid-like structure known as a lattice structure.
What is lattice enthalpy?
The amount of energy required to completely separate one mole of the solid ionic compound into constituent gaseous ions is known as lattice enthalpy.
How does the charge on the ion affect lattice enthalpy?
The ions in the lattice crystal are attracted due to an electrostatic force of attraction present between them. This force is directly proportional to the magnitude of charge, hence higher the charge stronger the lattice enthalpy.
How does the size of the atom affect lattice enthalpy?
Smaller atoms have smaller interatomic distances and so have a stronger binding force. This results in higher lattice enthalpy.