chemistry

123456789
Across
  1. 2. smallest particle of a chemical element
  2. 6. a tabular arrangement of the chemical elements
  3. 7. a subatomic particle with the same mass as a proton but without an electric charge
  4. 8. a stable subatomic particle with negative charge
  5. 9. any four substances (earth air fire and water)
Down
  1. 1. two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons
  2. 3. to make a feature of the world easier to understand
  3. 4. the emission of energy as electronic waves
  4. 5. a stable subatomic particle in all atoms
  5. 7. the central and most important part of an object