States of Matter
Elementary School
Definition
The physical forms in which matter exists—solid, liquid, and gas—determined by how its particles are arranged and how much energy they have. Solids hold their shape, liquids flow and take their container's shape, and gases spread to fill any space.
Worked examples
Ice (solid) melts to water (liquid) at \(0\,^\circ\)C\(\), then boils to steam (gas) at \(100\,^\circ\)C\(\).
The same substance changes state as energy increases, showing how particle arrangement and energy determine the state.
A rock keeps its shape and volume (solid); juice pours into a cup and takes its shape (liquid); helium fills an entire balloon (gas).
Each state has distinct properties based on how tightly its particles are packed and how freely they move.
Common mistakes
- Liquids have no definite volume and expand to fill their container. → Liquids have a definite volume but take the shape of their container. Only gases expand to fill all available space; liquids maintain a fixed volume.
- Gas particles are larger than liquid or solid particles of the same substance. → The particles are the same size; gases just have much more space between them. State changes affect spacing and energy, not the size of individual particles.
- Solids cannot move their particles at all. → Solid particles vibrate in fixed positions but do not flow past each other. All matter's particles have some kinetic energy and motion, even in solids.
Where you'll use it next
You'll use states of matter when studying phase changes and energy transfer, explaining weather phenomena like evaporation and condensation, and later in chemistry when exploring intermolecular forces and phase diagrams.
See also
Reviewed by Pat Cheng, M.Ed. — StudyPug Curriculum Lead · Last updated June 6, 2026