Here's a breakdown:

* Molecular Arrangement:

* Solids: Molecules in solids are tightly packed in a fixed, ordered structure (lattice). They have strong intermolecular forces holding them together, restricting their movement.

* Liquids: Molecules in liquids are more loosely packed than in solids and have more freedom to move around. While they maintain some order, it's less rigid than in solids.

* Intermolecular Forces:

* Solids: Strong intermolecular forces like ionic bonds or metallic bonds keep molecules in their fixed positions, resisting expansion.

* Liquids: While weaker than solids, liquids still have intermolecular forces that can be overcome with added energy (heat).

* Heat Energy:

* When you heat a substance, you add energy, causing its molecules to move faster.

* In solids, the molecules vibrate more strongly but remain in their fixed positions.

* In liquids, the increased energy allows molecules to move farther apart, leading to greater expansion.

In simpler terms: Imagine solid molecules as tightly packed marbles in a box. When heated, they vibrate more but stay in place. Now imagine liquid molecules as marbles loosely arranged in a bag. Heating them allows the marbles to move around and spread out more, causing the bag to expand.

Key takeaway: The more freedom of movement that molecules have in a substance, the more they can spread out when heated, resulting in greater expansion. This is why liquids, with their more loosely packed and mobile molecules, expand more than solids.