Which one has the highest melting point ?

Options

A. Ionic crystal
B. Molecular crystal
C. Covalent crystal
D. Metallic crystal

Answer

To determine which type of crystal has the highest melting point among ionic crystals, molecular crystals, covalent crystals, and metallic crystals, we can analyze the properties of each type of crystal.

### Step-by-Step Solution:

1. **Understanding Melting Point**:
- The melting point is the temperature at which a solid becomes a liquid. It is influenced by the types of bonds and forces present in the crystal structure.

**Hint**: Remember that stronger bonds typically lead to higher melting points.

2. **Ionic Crystals**:
- Ionic crystals are composed of positive and negative ions held together by strong electrostatic forces (ionic bonds). These crystals are generally hard and brittle and have high melting points due to the significant energy required to break the ionic bonds.

**Hint**: Consider the strength of the ionic bonds when thinking about melting points.

3. **Molecular Crystals**:
- Molecular crystals are formed by molecules held together by weaker intermolecular forces such as van der Waals forces, dipole-dipole interactions, and hydrogen bonds. As a result, they typically have low melting and boiling points compared to ionic and covalent crystals.

**Hint**: Weak intermolecular forces lead to lower melting points.

4. **Covalent Crystals**:
- Covalent crystals consist of a three-dimensional network of atoms connected by strong covalent bonds. These structures are very hard and have very high melting points because breaking covalent bonds requires a significant amount of energy.

**Hint**: Strong covalent bonds contribute to very high melting points.

5. **Metallic Crystals**:
- Metallic crystals are held together by metallic bonds, which involve the attraction between positively charged metal ions and a sea of delocalized electrons. The melting point of metallic crystals can vary widely depending on the metal, but they generally have moderate to high melting points.

**Hint**: The melting point of metals can vary, but they are usually not as high as covalent crystals.

6. **Comparison of Melting Points**:
- Based on the analysis:
- Ionic crystals have high melting points.
- Molecular crystals have low melting points.
- Covalent crystals have very high melting points due to strong covalent bonds.
- Metallic crystals have moderate to high melting points.

7. **Conclusion**:
- Among the four types of crystals, covalent crystals have the highest melting point due to the presence of strong covalent bonds that form a giant three-dimensional network.

**Final Answer**: Covalent crystals have the highest melting point.