Pure covalent molecules are ususlly held in a crystal structure by

Options

A. Dipole-dipole attractin
B. Electrostatic attraction
C. Hydrogen bonds
D. Vander Waal's attraction

Answer

To answer the question, "Pure covalent molecules are usually held in a crystal structure by?", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Pure Covalent Bonds**:
- Pure covalent bonds occur when two atoms share electrons equally. This typically happens when the atoms involved have the same or very similar electronegativities. An example of this is the bond between two chlorine atoms (Cl-Cl).

2. **Identifying the Nature of Attraction in Pure Covalent Crystals**:
- In pure covalent crystals, the molecules are held together by weak intermolecular forces. Since there is no significant difference in electronegativity, the primary attractive forces are not ionic or dipole-dipole interactions.

3. **Types of Intermolecular Forces**:
- The main types of intermolecular forces include:
- **London Dispersion Forces**: These are weak forces that arise from temporary shifts in electron density in molecules, leading to temporary dipoles.
- **Dipole-Dipole Interactions**: These occur in polar molecules where there is a significant difference in electronegativity.
- **Hydrogen Bonding**: A strong type of dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine.

4. **Conclusion**:
- In pure covalent crystals, the dominant forces holding the molecules together are **London Dispersion Forces**. These forces are present in all molecules, but they are the primary attractive force in pure covalent substances where there is no significant electronegativity difference.

### Final Answer:
Pure covalent molecules are usually held in a crystal structure by **London Dispersion Forces**.

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