# Matter is made of atoms and molecules

> The particle picture behind every metal and compound


## Objectives

- Describe matter as tiny particles that are always moving, with spaces between them.
- Tell an atom from a molecule.
- Tell a molecule of an element from a molecule of a compound.

## 1. Matter is made of atoms and molecules: from zero




## 2. Gaps in the rails

Predict:

- Because solid metal never changes its size
- Because the metal gets longer when it gets hot ✓
- To use less metal

The gaps are there because metal gets longer when it gets hot: its particles vibrate more and spread out. The gaps leave room for that expansion.

[ar-EG] الفراغات دي موجودة عشان الـ metal بيطول لما يسخن: الـ particles بتاعته بتهتز أكتر وتتباعد. والفراغات بتسيب مكان للتمدد ده.
## 3. Tiny particles, always moving

Atom The smallest building unit of matter that can take part in chemical reactions. A solid metal: the atoms vibrate in place, with small spaces between them. All matter is made of tiny particles. The particles are always moving. In a solid, they vibrate in place. There are spaces between the particles. The particles of a solid do not move.


## 4. Atoms join into molecules

Molecule The smallest part of a substance that can exist freely and has the properties of that substance. Molecule of an element $\ce{O2}$: two atoms of the **same** kind. Molecule of a compound $\ce{H2O}$: atoms of **different** kinds (2 H + 1 O). Count the kinds of atom A metal such as iron is built from a huge number of iron atoms. A molecule must be made of different atoms.


## 5. Element or compound?

Sort each molecule. In a solid iron nail, the particles do not move at all.


## 6. Summary

Matter is made of tiny particles, always moving, with spaces between them. Back to the hook: heated rail particles vibrate more and need more space. A molecule is made of atoms of one kind ($\ce{O2}$) or of different kinds ($\ce{H2O}$). Where you will meet it Ch.1 p.13: paramagnetism appears in **ions or atoms or molecules** with unpaired electrons. Can you explain why $\ce{O2}$ is a molecule but not a compound? $\ce{O2}$ is made of two atoms of the same kind, so it is a molecule of an element. A molecule of a compound has atoms of different kinds, like $\ce{H2O}$.



Chapter: Transition Elements (https://yaani.ai/en/learn/chemistry/chem-s3-en.ch1)
Source: https://yaani.ai/en/lesson/chem-s3-en.lesson-sci.matter-particles