# States of matter, melting and boiling points

> When a solid lets go


## Objectives

- Name the three states of matter and the changes between them.
- Define the melting point and the boiling point.
- Link stronger forces between particles to higher melting and boiling points.

## 1. General properties: mass, radius and metallic property




## 2. Ice and iron

Predict: what decides how high a substance's melting point is?

- The size of the piece
- How fast you heat it
- How strongly its particles hold each other ✓

To melt, the particles must partly break free, so the melting point depends on how strongly they hold each other. The size of the piece and how fast you heat it do not change the temperature at which melting starts.

[ar-EG] عشان المادة تسيح، الـ particles لازم تفلت من بعضها جزئيًا، فالـ melting point بتعتمد على قد إيه الـ particles ماسكة في بعض. حجم الحتة وسرعة التسخين مش بيغيّروا درجة الحرارة اللي الـ melting بيبدأ عندها.
## 3. Melting point

Matter is solid, liquid or gas Melting point The temperature at which a solid changes into a liquid. Pure ice melts at 0 °C. Below it, water is solid; above it, liquid.


## 4. Heat the water

Boiling point The temperature at which a liquid changes into a gas (vapour). Heat pure water at normal air pressure. Watch its particles. temperature Solid: particles vibrate in fixed places. 0 °C, the melting point: solid turns into liquid. Liquid: particles slide past each other. 100 °C, the boiling point: liquid turns into gas. Gas: particles are far apart and move freely.


## 5. Stronger forces, higher values

Melting points of some familiar substances To melt or boil, particles must break free from their neighbours. So the **stronger the forces** between the particles, the **higher** the melting and boiling points.


## 6. Read the numbers

Substance A melts at 45 °C. Substance B melts at 1085 °C. Which has stronger forces between its particles?

- You can't tell without the mass of each sample
- A
- B ✓

B melts at a much higher temperature, so its particles need far more heating to break free: the forces between them are stronger. A melting point does not depend on the mass of the sample.

[ar-EG] الـ B بتسيح عند درجة حرارة أعلى بكتير، يعني الـ particles بتاعتها محتاجة تسخين أكتر بكتير عشان تفلت، فالـ forces بينها أقوى. والـ melting point مش بتعتمد على كتلة العينة.
## 7. Summary

Stronger forces between particles → higher melting and boiling points Matter is solid, liquid or gas. Melting point: solid → liquid. Boiling point: liquid → gas. Stronger forces between particles → higher melting and boiling points. Next in Chapter 1: transition metals melt at very high temperatures. Why? Can you explain why a high melting point means strong forces between particles?



Chapter: Transition Elements (https://yaani.ai/en/learn/chemistry/chem-s3-en.ch1)
Source: https://yaani.ai/en/lesson/chem-s3-en.lesson-phys.states-melting-boiling