atomic theory

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Across
  1. 3. the smallest unit of ordinary matter that forms a chemical element.
  2. 5. appearing or occurring at intervals.
  3. 7. relating to an atom or atoms.
  4. 9. an essential or characteristic part of something abstract.
  5. 13. an inert gaseous element of the noble gas group
  6. 15. a colourless, odourless reactive gas
  7. 16. a rare radioactive gas belonging to the noble gas series.
  8. 18. a substance made by mixing other substances together.
  9. 19. a silver-white metal of the alkaline earth series
  10. 20. a stable subatomic particle with a charge of negative electricity
Down
  1. 1. a stable subatomic particle occurring in all atomic nuclei
  2. 2. A chemical compound is a chemical substance composed of many identical molecules composed of atoms from more than one element held together by chemical bonds.
  3. 4. the emission of ionizing radiation or particles caused by the spontaneous disintegration of atomic nuclei.
  4. 6. a non-metal which has two main forms
  5. 8. a subatomic particle of about the same mass as a proton but without an electric charge
  6. 10. a hard grey metal of the transition series
  7. 11. a radioactive metal occurring in nature only as a product of radioactive decay of uranium.
  8. 12. a hard silver-grey metal of the transition series
  9. 14. a colourless, odourless, highly flammable gas
  10. 17. are variants of a particular chemical element which differ in neutron number