Level: JHS, Basic 8 | Subject: Integrated Science | Strand: Diversity of Matter | Topic: Materials
Curriculum reference: B8.1.1.1 Demonstrate understanding of the concept of atom, molecule and atomicity of elements. Indicator B8.1.1.1.1: Explain atoms, molecules and atomicity of elements. All the exemplars are merged into one set of notes.
1. The Atom
- An atom is the smallest particle of an element that can take part in a chemical reaction.
- All matter is made of atoms: the water we drink, the iron nail, the air we breathe.
- An atom has a small centre called the nucleus. The nucleus contains protons (positive charge) and neutrons (no charge).
- Electrons (negative charge) move round the nucleus.
- An atom has no overall charge because the number of protons equals the number of electrons.
2. Models and Diagrams of Atoms
Scientists use models to show what an atom looks like. In a simple model, the nucleus is drawn in the middle as a circle with protons (+) and neutrons. The electrons are drawn as small dots on rings round the nucleus. You can build a model in class with clay, beads or bottle tops.
| Particle | Charge | Where found |
|---|---|---|
| Proton | Positive (+) | Nucleus |
| Neutron | None | Nucleus |
| Electron | Negative (-) | Round the nucleus |
3. The Molecule
- A molecule is a group of two or more atoms joined together.
- A molecule of an element has atoms of the same kind. Example: oxygen (O2) has two oxygen atoms.
- A molecule of a compound has atoms of different kinds. Examples: water (H2O) has two hydrogen atoms and one oxygen atom; carbon dioxide (CO2) has one carbon atom and two oxygen atoms.
4. Atomicity
Atomicity is the number of atoms in one molecule of an element.
| Atomicity | Meaning | Examples |
|---|---|---|
| Monoatomic | One atom in a molecule | Helium (He), neon (Ne), argon (Ar) |
| Diatomic | Two atoms in a molecule | Hydrogen (H2), oxygen (O2), nitrogen (N2), chlorine (Cl2) |
| Triatomic | Three atoms in a molecule | Ozone (O3) |
| Polyatomic | Four or more atoms in a molecule | Phosphorus (P4), sulphur (S8) |
The small number written below a symbol tells how many atoms are in the molecule. Metals such as iron (Fe) and copper (Cu) are written with one atom, as Fe and Cu.
Remember: An atom is the smallest particle of an element. A molecule is two or more atoms joined together. Atomicity is the number of atoms in a molecule of an element.
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Education Always (education.inspiringalways.com). Original notes written to follow the NaCCA Basic 8 Integrated Science curriculum.
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