(a) solids, liquids and gases in terms of the spacing, ordering and motion…

The idea

This statement asks you to describe the three states of matter using three linked ideas: how far apart the atoms or molecules are (spacing), how regularly they are arranged (ordering), and how they move (motion). In a solid, particles are close together and held in a regular lattice, vibrating about fixed mean positions. In a liquid, particles remain close but are randomly arranged, so they can slide past one another while staying in contact. In a gas, particles are far apart with no regular ordering and move rapidly and randomly, colliding with each other and the container walls. A useful method is to compare the same substance, such as water, as ice, liquid water and steam, and ask which of the three features changes most. MCQ items often test one feature at a time, so read each option carefully and reject any that mixes up ordering with spacing.

What earns the marks

• Solids: particles closely spaced and arranged in a regular, ordered lattice.
• Solids: particles vibrate about fixed mean positions rather than moving from place to place.
• Liquids: particles closely spaced but arranged randomly, with no long-range order.
• Liquids: particles are free to slide past one another while remaining in contact.
• Gases: particles are widely spaced with negligible ordering.
• Gases: particles move rapidly and randomly, colliding with each other and with the container walls.

Common mistakes and how to put them right

• Thinking that particles in a solid do not move at all.

  Put it right: In fact they vibrate about fixed mean positions, so the motion is present but restricted.

• Believing that liquid particles are far apart because liquids flow.

  Put it right: In fact liquid particles remain close together and it is their random arrangement that allows sliding.

• Assuming gas particles are ordered because they fill a container uniformly.

  Put it right: In fact they are randomly arranged and it is their rapid random motion that spreads them throughout the container.

• Confusing spacing with ordering, for example describing a liquid as having a regular lattice simply because its particles are close together.

Exam tips

• For each option, identify which of spacing, ordering or motion it describes, then check it against the correct state.
• Use a three-column comparison table for solid, liquid and gas to make the differences explicit before answering.
• Reject any option that describes a solid as having no motion or a gas as having a fixed arrangement.
• Link each description to a familiar substance so the reasoning stays concrete rather than abstract.