Molecular structure of solids, liquids and gases
In nature water occurs in three states: solid (ice), liquid (water) and gas (steam). Their molecules are the same — the difference is in how the molecules are arranged and how they move. In a gas the molecules are far apart and move constantly and randomly, and the attractive force between them is very small. So a gas fills both the shape and the whole volume of its container and is easily compressed: it has neither its own shape nor its own volume. In a liquid the molecules are close and the attraction is noticeable, so a liquid keeps its volume but cannot keep its shape and takes the shape of the vessel; it is very hard to compress. In a solid the molecules (atoms) are closest and arranged in order, vibrating about their places: it keeps its own shape and volume. In a crystal of table salt NaCl, sodium and chlorine atoms form a crystal lattice. The way atoms are arranged changes the properties: pencil graphite and diamond both consist of carbon atoms but are arranged differently.
“Squeezing in a syringe” (needle-free syringe, with an adult): (1) fill the syringe with air, close the tip with a finger and press the plunger — the air compresses; (2) repeat with the syringe filled with water — the water hardly compresses. Safety: use only a needle-free syringe; do not spray water at eyes. Link the results to the arrangement of gas and liquid molecules.