Classify the following as amorphous or crystalline solids: polyurethane, naphtalene, benzoic acid, teflon, potassium nitrate, cellophane, polyvinyl chloride, fibre glass, copper.

Answer

To classify the given substances as amorphous or crystalline solids, we need to understand the characteristics of each type of solid:

1. **Crystalline Solids**: These solids have a well-defined, ordered arrangement of particles. They form a regular geometric structure and have distinct melting points.

2. **Amorphous Solids**: These solids do not have a long-range order in their arrangement of particles. They are often isotropic and do not have a definite melting point; instead, they soften over a range of temperatures.

Now, let's classify the given substances step by step:

### Step 1: Classify Polyurethane
- **Polyurethane** is a type of plastic that does not have a regular arrangement of particles.
- **Classification**: Amorphous Solid

### Step 2: Classify Naphthalene
- **Naphthalene** is a molecular solid that has a well-defined crystalline structure.
- **Classification**: Crystalline Solid

### Step 3: Classify Benzoic Acid
- **Benzoic Acid** is also a molecular solid with a regular arrangement of particles.
- **Classification**: Crystalline Solid

### Step 4: Classify Teflon
- **Teflon** is another type of plastic that lacks a regular arrangement of particles.
- **Classification**: Amorphous Solid

### Step 5: Classify Potassium Nitrate
- **Potassium Nitrate** is an ionic compound that has a well-defined crystalline structure.
- **Classification**: Crystalline Solid

### Step 6: Classify Cellophane
- **Cellophane** is a type of plastic that does not have a regular arrangement of particles.
- **Classification**: Amorphous Solid

### Step 7: Classify Polyvinyl Chloride (PVC)
- **Polyvinyl Chloride (PVC)** is a synthetic plastic polymer that does not have a regular arrangement of particles.
- **Classification**: Amorphous Solid

### Step 8: Classify Fiber Glass
- **Fiber Glass** is a composite material that is also considered amorphous due to its irregular structure.
- **Classification**: Amorphous Solid

### Step 9: Classify Copper
- **Copper** is a metallic solid that has a well-defined crystalline structure.
- **Classification**: Crystalline Solid

### Summary of Classifications:
- **Amorphous Solids**: Polyurethane, Teflon, Cellophane, Polyvinyl Chloride, Fiber Glass
- **Crystalline Solids**: Naphthalene, Benzoic Acid, Potassium Nitrate, Copper