No, the particles themselves in a gas, liquid, and solid are not the same weight. The weight of a particle is determined by its atomic mass.

Here's why it's a bit tricky:

* The same substance can be a gas, liquid, or solid: Think of water (H₂O). The water molecules in ice (solid), liquid water, and water vapor (gas) all have the same weight because they are made of the same atoms.

* The difference is in the spacing and movement: What changes is how close the particles are to each other and how they move.

* In a solid, particles are tightly packed and vibrate in place.

* In a liquid, particles are more spread out and can move around each other.

* In a gas, particles are very spread out and move freely.

To summarize: The particles themselves don't change weight when a substance changes state, but the overall density and volume of the substance do change.