Q1.
In which of the above six objects do you think particles are strongly held together?
Answer
In all six — every one of them is a solid, and in a solid the interparticle attractions are always very strong. That is why each of them has a definite shape and a definite volume that hammering does not simply squash away.
If you compare them with one another, the hammer sorts them into three kinds of behaviour:
| Object | What hammering does | What it suggests |
|---|---|---|
| Iron nail, key, piece of aluminium | Dents and flattens, but stays in one piece | Attractions strong, and the particles keep holding on to one another even as they are pushed into new positions |
| Rock salt, stone | Cracks and crumbles into smaller pieces | Attractions are strong too — the pieces are simply groups of particles separated from other groups, and each piece is still hard |
| Wooden block | Dents, and splits if struck hard | Held together strongly enough to keep its shape and volume |
Of the six, the iron nail resists the hammer most, and Table 7.1 supports that reading: iron melts only at 1538 °C, while ice melts at 0 °C. A high melting point means a lot of thermal energy is needed before the particles can be pulled out of their fixed positions — that is, the interparticle attractions are especially strong.
Read the crumbling correctly: rock salt breaking is not evidence of weak attraction. Hammering separates whole groups of particles from other groups; it does not tell you how hard it is to move one particle away from its neighbour. The melting point does.