**Density: States of Matter and Its Properties**

**Definition of Density:**
Density is a physical property of matter that describes the amount of mass per unit volume. It is a measure of how tightly packed the particles of a substance are. The formula for density is given by:

Density = Mass / Volume

**States of Matter:**
Matter exists in three main states: solid, liquid, and gas. Each state has its own unique characteristics and properties.

1. **Solid:** In the solid state, particles are closely packed together and have a fixed shape and volume. The intermolecular forces between particles are strong, causing them to vibrate in fixed positions. Solids have a high density due to the close arrangement of particles.

2. **Liquid:** Liquids have particles that are close together but not as tightly packed as in solids. They do not have a fixed shape, taking the shape of their container, but they have a fixed volume. The intermolecular forces in liquids are weaker than in solids, allowing particles to move more freely. Liquids have a lower density than solids.

3. **Gas:** Gases have particles that are far apart and move freely in all directions. They have neither a fixed shape nor volume, as they completely fill the container they are in. The intermolecular forces in gases are very weak. Gases have the lowest density among the three states of matter.

**Density and States of Matter:**
Density is directly related to the state of matter. The density of a substance can change when it undergoes a change in state.

1. **Melting:** When a solid is heated, it absorbs energy and its particles gain enough kinetic energy to overcome the intermolecular forces holding them together. The solid then melts and becomes a liquid. During melting, the density of the substance generally decreases as the particles become less closely packed.

2. **Boiling / Evaporation:** When a liquid is heated, it also absorbs energy and its particles gain enough kinetic energy to overcome the intermolecular forces. The liquid then boils and becomes a gas. During boiling, the density of the substance decreases even further as the particles move even farther apart.

3. **Condensation:** The reverse process of boiling is condensation. When a gas loses energy, its particles lose kinetic energy and come closer together. The gas condenses to form a liquid, and its density increases.

**Conclusion:**
Density is a property of matter that helps us understand the arrangement of particles in different states of matter. Solids have the highest density, followed by liquids, and gases have the lowest density. Changes in state, such as melting, boiling, and condensation, can affect the density of a substance. Understanding density and its relationship with the states of matter is crucial in various scientific and practical applications.

Density is use to describe how much space an object or substance takes up (its volume) in relation to the amount of matter in that object or substance (its mass). 
Density is the amount of mass per unit of volume.