Atoms, Ions and Isotopes

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Across
  1. 2. Fe
  2. 3. neutrally charged subatomic particle
  3. 8. describes outermost shell/electrons
  4. 9. He
  5. 12. negative ion
  6. 15. centre of an atom
  7. 17. 4 or less electrons
  8. 18. an atom with a different number of neutrons
  9. 19. when an atom has a full outer shell
Down
  1. 1. positive ion
  2. 4. the smallest of the three subatomic particles
  3. 5. maximum number of electrons in first shell
  4. 6. 5 or more electrons
  5. 7. positively charged subatomic particle
  6. 10. protons plus neutrons
  7. 11. atom with an imbalance of protons and electrons
  8. 13. columns of a periodic table
  9. 14. rows of a periodic table
  10. 16. maximum number of electrons in second and third shell