Across
- 2. smallest particle of a chemical element
- 6. a tabular arrangement of the chemical elements
- 7. a subatomic particle with the same mass as a proton but without an electric charge
- 8. a stable subatomic particle with negative charge
- 9. any four substances (earth air fire and water)
Down
- 1. two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons
- 3. to make a feature of the world easier to understand
- 4. the emission of energy as electronic waves
- 5. a stable subatomic particle in all atoms
- 7. the central and most important part of an object