Particles and states of matter

Closely packed in a fixed, regular pattern

HintThey are locked in place and cannot swap positions, only vibrate.

The whyBecause the particles are held in a fixed lattice and can only vibrate, a solid keeps its own shape and cannot be compressed.

Quickly and randomly in all directions

HintWith almost nothing holding them, they fly about and fill any space.

The whyGas particles have lots of energy and are widely spaced, so a gas has no fixed shape or volume and can be squashed into a smaller space.

Melting

HintIt is what ice does on a warm day.

The whyHeating gives the particles enough energy to break out of their fixed pattern, so the solid structure gives way and it flows as a liquid.

It stays constant

HintEnergy is being given out as the structure locks together, so the reading holds still.

The whyDuring freezing the energy released as particles lock into place keeps the temperature fixed until all the liquid has solidified.

Boiling

HintIt is the one that makes bubbles rise from the bottom of the pan.

The whyEvaporation happens only at the surface and at any temperature; boiling happens all through the liquid at its fixed boiling point.

The surface

HintOnly the topmost particles, in contact with the air, can escape.

The whyAt the surface, the fastest particles can escape into the air. This can happen at any temperature, which is why a puddle dries up without boiling.

Diffusion

HintIt is how the smell of baking travels across a room with no fan.

The whyParticles in liquids and gases move randomly, so over time they spread out evenly from where they are concentrated — no stirring required.

Particles colliding with the walls

HintBillions of tiny moving bits keep bumping the sides.

The whyEach collision gives a tiny push. Countless particles hitting the walls every second add up to the steady outward pressure of the gas.

Into the gaps between the water particles

HintThe sugar is still there after it dissolves — so where could it be hiding out of sight?

The whyThe sugar particles spread out and hide in the gaps between the solvent particles, so the solution looks clear even though the sugar is still there.

same

HintNo particles are lost, so nothing is added to or taken from the reading on the balance.

The whyDissolving does not destroy any particles — they are all still present, just spread out — so the mass of the solution equals the salt plus the water.

It is made of only one type of particle

HintNothing else is mixed in — a single kind throughout.

The whyIn everyday speech 'pure' can mean 'natural', but in chemistry it strictly means one substance only — one kind of particle, with nothing else present.

Changing state

HintThe energy is busy rearranging particles, not making them hotter.

The whyDuring melting or boiling the energy supplied breaks the forces between particles rather than raising the temperature, so the graph levels off.