Scientific Method and Periodic Table Crossword Puzzle

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Across
  1. 4. vertical columns in the periodic table called
  2. 5. Fe is the symbol for what element
  3. 6. this step involves using the 5 senses
  4. 9. electrons in the outermost shell
  5. 10. most abundant elements of the periodic table
  6. 12. the difference between atomic mass and atomic number
  7. 13. equals the number of protons
  8. 14. horizontal columns in the periodic table
  9. 15. minimum times an experiment should be conducted
  10. 16. number of electrons in the second and third shell
  11. 17. variable that is measured
  12. 18. these elements have the nickname of the staircase
  13. 19. most exciting step of the scientific method
  14. 20. final step of the scientific method
Down
  1. 1. equals the number of protons
  2. 2. written as an if then statement
  3. 3. found in the nucleus
  4. 7. number of electrons in the first shell/cloud/energy level
  5. 8. pure substance made up of only one atom
  6. 11. what is changed in an experiment/testing