Which melts first?
Weak attraction, low melting point. Strong attraction, high melting point.
Ice, urea and iron
Ice, urea and iron are all solids. Each one is heated until it melts.
Which one do you think needs the highest temperature to melt?
What this lesson covers
The idea
Solids with weak interparticle forces of attraction have low melting points, while those with strong attractive forces have high melting points.
Ice, urea and iron
Ice, urea and iron are all solids. Each one is heated until it melts.
Which one do you think needs the highest temperature to melt?
- Iron
- Urea
- Ice
Heat each solid
The lines between the particles show how strongly they attract. Heat each solid until it melts.
Attraction and melting point
Solids with weak interparticle forces of attraction have low melting points. Solids with strong attractive forces have high melting points.
Of these three, the particles of iron attract each other most strongly, and those of ice least strongly.
- Solid | Melting point
- Ice | 0 °C
- Urea | 133 °C
- Iron | 1538 °C
Notes
Weak interparticle attractions: low melting point. Strong attractive forces: high melting point. Ice 0 °C, urea 133 °C, iron 1538 °C.
Check yourself
A solid has a very high melting point. What can you say about the attraction between its particles?
Which of these solids has the weakest attraction between its particles?
Iron melts at 1538 °C and urea at 133 °C. How many degrees higher is the melting point of iron?
Answer: 1405 °C
1538 − 133 = 1405 °C. Iron's particles attract each other much more strongly.
Why does ice melt at a much lower temperature than iron?
- There is no attraction at all. The particles of every solid are held together by attractions.
- It is weak. Weak attractions give a low melting point.
- It is strong — correct. Yes. Strong attractive forces give a high melting point.
- Urea (melting point 133 °C). Urea melts at a higher temperature than ice, so its attractions are stronger.
- Ice (melting point 0 °C) — correct. Yes. It has the lowest melting point of the three.
- Iron (melting point 1538 °C). Iron has the highest melting point, so its attractions are the strongest.
- The attraction between particles of ice is weaker — correct. Yes. Weak attractions mean a low melting point.
- Ice is lighter than iron. Weight is not the reason. The strength of the attractions is.
- Ice has no particles. Ice is made of particles too. They are held by weaker attractions.