01Structure of the atom
An atom has a tiny, dense nucleus at its centre, containing positively-charged protons and neutral neutrons.
Negatively-charged electrons move around the nucleus in shells (energy levels). Atoms are mostly empty space.
- Proton — positive charge, in the nucleus
- Neutron — no charge, in the nucleus
- Electron — negative charge, orbits the nucleus
02Elements and the periodic table
An element is a substance made of only one type of atom — it cannot be broken down into anything simpler by chemical means.
The periodic table arranges all known elements by their properties. Each element has a chemical symbol, such as O for oxygen or Na for sodium.
03Compounds and chemical bonds
A compound forms when atoms of two or more different elements join together in a fixed ratio, through a chemical reaction, creating chemical bonds.
A compound has completely different properties from the elements that made it.
04Mixtures vs compounds
In a mixture, substances are only physically combined (not chemically bonded), so they keep their own properties and can be separated by physical methods.
In a compound, the elements are chemically bonded and can only be separated by chemical reactions.
05Chemical formulas
A chemical formula shows which elements are in a compound, and how many atoms of each. For example, H₂O means 2 hydrogen atoms bonded to 1 oxygen atom.
| Term | 한국어 | Meaning |
|---|---|---|
| atom | 원자 | The smallest particle of an element |
| proton | 양성자 | Positively charged particle in the nucleus |
| neutron | 중성자 | Neutral particle in the nucleus |
| electron | 전자 | Negatively charged particle orbiting the nucleus |
| element | 원소 | A substance made of only one type of atom |
| compound | 화합물 | Two or more elements chemically bonded together |
| mixture | 혼합물 | Substances physically combined, not chemically bonded |