Here's why:
* Particle arrangement: Gas particles are very far apart and move randomly in all directions.
* Weak intermolecular forces: The forces of attraction between gas molecules are very weak.
* High kinetic energy: Gas particles have high kinetic energy, meaning they move quickly and collide frequently.
Because of these factors, gas molecules are not held together in a fixed arrangement, and they will expand to fill any container they are placed in.
Think of it this way: Imagine a room full of bouncy balls. If you open the door, the balls will spread out and fill the entire room, taking on the shape of the room. This is similar to how gas behaves.
Liquids and solids, on the other hand, have definite shapes because their particles are more closely packed and have stronger intermolecular forces.
