To determine which compound has the lowest melting point among lithium chloride (LiCl), cesium chloride (CsCl), rubidium chloride (RbCl), and potassium chloride (KCl), we can follow these steps:
### Step-by-Step Solution:
1. **Identify the Compounds**: The compounds we are considering are LiCl, CsCl, RbCl, and KCl. All of these compounds are salts formed from alkali metals and chlorine.
2. **Understand the Trend in Melting Points**: In the alkali metal group (Group 1 of the periodic table), as we move down the group from lithium (Li) to cesium (Cs), the size of the metal cation increases.
3. **Relate Atomic Size to Lattice Energy**: The melting point of ionic compounds is influenced by lattice energy, which is the energy required to separate the ions in the solid state. As the size of the cation increases, the lattice energy decreases because the distance between the ions increases, leading to weaker ionic bonds.
4. **Consider the Effect of Covalent Character**: Lithium chloride (LiCl) has a significant covalent character due to the small size of the lithium ion, which leads to a lower melting point compared to other alkali metal chlorides. This is because covalent bonds generally have lower melting points than ionic bonds.
5. **Compare the Melting Points**: The melting points of the compounds are as follows:
- LiCl: 883 K
- NaCl: 1081 K
- KCl: 1045 K
- RbCl: 990 K
- CsCl: (not provided but generally higher than LiCl)
6. **Conclusion**: Based on the melting points and the reasoning above, lithium chloride (LiCl) has the lowest melting point among the given compounds.
### Final Answer:
The compound with the lowest melting point is **lithium chloride (LiCl)**.
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To determine which compound has the lowest melting point among lithium chloride (LiCl), cesium chloride (CsCl), rubidium chloride (RbCl), and potassium chloride (KCl), we can follow these steps:
### Step-by-Step Solution:
1. **Identify the Compounds**: The compounds we are considering are LiCl, CsCl, RbCl, and KCl. All of these compounds are salts formed from alkali metals and chlorine.
2. **Understand the Trend in Melting Points**: In the alkali metal group (Group 1 of the periodic table), as we move down the group from lithium (Li) to cesium (Cs), the size of the metal cation increases.
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