Matter is made of atoms and molecules
The particle picture behind every metal and compound
1. Matter is made of atoms and molecules: from zero
2. Gaps in the rails
Railway tracks are laid with small gaps between the steel rails. Why leave gaps in solid metal?
Pick the right answer
Predict:
- A. To use less metal
- B. Because the metal gets longer when it gets hot
- C. Because solid metal never changes its size
الشرح
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.
3. Tiny particles, always moving
Atom
The smallest building unit of matter that can take part in chemical reactions.
- 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.
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
O2: two atoms of the same kind.
Molecule of a compound
H2O: atoms of different kinds (2 H + 1 O).
| Molecule | Atoms | Kinds of atom | Molecule of |
|---|---|---|---|
| O2 | 2 O | 1 | an element |
| H2O | 2 H + 1 O | 2 | a compound |
A metal such as iron is built from a huge number of iron atoms.
5. Element or compound?
Sort into groups
Sort each molecule.
N2CO2Cl2NH3CO
True or false?
In a solid iron nail, the particles do not move at all.
الشرح
Particles of matter are always moving. In a solid they vibrate in place.
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 (O2) or of different kinds (H2O).
Can you explain why O2 is a molecule but not a compound?
Reveal
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 H2O.