The bonds between ions of opposite charge is strongest when the ions are small, the lattice energy of LiF is more exothermic than the lattice energy of CsI. Explain.
To understand why the bonds between ions of opposite charge are strongest when the ions are small, and why the lattice energy of LiF is more exothermic than the lattice energy of CsI, we need to consider several factors: the size of the ions, the magnitude of the charges, and the distance between the ions.
Ionic bonds are formed when a metal donates electrons to a nonmetal, resulting in the formation of positive metal ions (cations) and negative nonmetal ions (anions). These ions are then attracted to each other due to their opposite charges.
1. Size of the ions:
The size of the ions plays a crucial role in determining the strength of the ionic bond. When the ions are small, they can approach each other more closely, which increases the strength of the attraction between them. On the other hand, when the ions are larger, the distance between them is greater, leading to a weaker bond.
2. Magnitude of the charges:
The magnitude of the charges on the ions also affects the strength of the ionic bond. Higher charges result in stronger attractive forces between the ions. Since the charges on the ions in LiF and CsI are both +1 and -1, we can assume that the charges have a comparable magnitude in both compounds.
3. Distance between the ions:
The distance between the ions is determined by the sum of their ionic radii. The smaller the sum of the radii, the closer the ions can get to each other, resulting in stronger bond formation. Hence, smaller ions favor the formation of stronger bonds.
Considering the above factors, let's analyze the difference between LiF and CsI:
LiF:
In lithium fluoride (LiF), both the lithium ion (Li+) and the fluoride ion (F-) are relatively small due to their atomic sizes. The small size of the ions allows them to approach each other closely, leading to a stronger attractive force between them. As a result, the lattice energy released during the formation of LiF is more exothermic.
CsI:
In cesium iodide (CsI), the cesium ion (Cs+) is much larger than the lithium ion in LiF, while the iodide ion (I-) is larger than the fluoride ion. The larger size of the ions in CsI results in a greater distance between them, leading to a weaker attractive force compared to LiF. Consequently, the lattice energy released during the formation of CsI is less exothermic than in LiF.
In summary, the bonds between ions of opposite charge are strongest when the ions are small because smaller ions can approach each other more closely. Consequently, the lattice energy of LiF is more exothermic than that of CsI due to the smaller size of the ions in LiF, allowing for a stronger attractive force between them.