Chapter 7: Particulate Nature of Matter (Chemistry)

In a solid the particles are packed close together and only vibrate about fixed positions. In a liquid they are still close, but they can move past one another, which is why liquids flow.

(iv)

1. True.
2. True. Heat makes the particles move faster, which weakens their hold on one another.
3. True.
4. True.
5. True. This happens by diffusion: camphor particles mix with the moving air particles and spread out.
6. False. Heat gives the camphor particles energy, so they escape into the air (it sublimes). What we smell is the camphor particles themselves reaching our nose. The energy is not "released as a smell".

(i)–(v) are true. (vi) is false: the camphor particles themselves spread through the air and reach our nose.

A chair is made of nothing but particles. Take them all away and there is nothing left: no material, no shape, no weight.

(iii) Nothing of the chair would remain, because matter is made entirely of particles.

In a gas, the particles are far apart and move fast and freely in all directions. The large spaces between them let the particles of another gas move in, so they mix quickly.

In a solid, the particles are tightly packed, held by strong attractions, and only vibrate in place. There is almost no space, and almost no movement, for mixing.

Gas particles are far apart and move freely, so they spread into one another; solid particles are packed tightly and fixed, so they cannot mix.

• Milk is a liquid. Its particles are close but can slide past one another, so it has no fixed shape. It flows and spreads over the table.
• The tumbler is a solid. Its particles are held in fixed positions by strong attractions, so it keeps its shape.

Milk's particles can slide past one another (a liquid flows); the glass's particles are held in fixed positions (a solid keeps its shape).

• Ice: particles closely packed in a regular pattern, vibrating in place.
• Water: still close together, but disordered and able to move past one another.
• Water vapour: particles far apart, moving quickly in all directions.

Ice: regular and tightly packed; water: close but disordered; vapour: far apart and moving freely.

1. Aluminium foil is a solid: particles in a closely packed, regular arrangement.
2. Glycerin is a liquid: particles close but irregular, able to slide past one another.
3. Methane is a gas: a few particles, far apart from one another.

Solid foil: regular and tightly packed; liquid glycerin: close but irregular; methane gas: widely spaced.

• Solid wax: the candle body and the hardened drips, matching the tightly packed, regular arrangement.
• Liquid wax: the melted pool around the wick, matching the close but irregular arrangement.
• Wax vapour (gas): the white smoke rising from the wick, matching the few, widely spaced particles.

Candle body → regular packed particles (solid); melted pool → close irregular particles (liquid); rising vapour → widely spaced particles (gas).

The salt has dissolved. Its particles have spread out and fitted into the spaces between the water particles. They are far too small to see, but they are still there, and our tongue tastes them.

If the water is evaporated, the salt particles come together again and appear as visible crystals.

Salt particles dissolve and spread into the spaces between water particles; they are too small to see but can still be tasted.

They are solids. Each grain, and each tiny particle of flour, has its own fixed shape and volume, and does not flow on its own like a liquid.

The heap seems to take the container's shape only because the separate small pieces can roll and slide over one another and fill the space.

Solids: each grain or flour particle keeps its fixed shape and volume; the pile only fills the jar because the separate pieces slide over one another.