Structure of the atom

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Across
  1. 2. the man who organized the periodic table by atomic mass
  2. 9. Symbol for sodium
  3. 10. Center of the atom
  4. 11. a row of elements
  5. 12. the building block of matter
  6. 14. salt forming
  7. 15. used in wiring and jewelry
  8. 19. the man who reorganized the p. table by atomic number(protons)
  9. 20. radioactive metals that are very dense
  10. 21. Scientist who developed the planetary model of the atom
  11. 24. sum of protons and neutrons (2 words)
  12. 26. a column of elements
  13. 29. negatively charged particle
  14. 30. Symbol for silver
  15. 31. Name of an element used in fluorescent signs
  16. 32. region surrounding the nucleus which is occupied by electrons (two words)
Down
  1. 1. they are the most reactive metals (two words)
  2. 3. non-reactive elements that have a full outer shell. (2 words)
  3. 4. a particle with approximately the same mass as a proton
  4. 5. element often made into electrical wire
  5. 6. rare earth metals
  6. 7. 1/12 the mass of a carbon -12 atom (3 words)
  7. 8. atom of an element with a different number of neutrons
  8. 13. separates the metals and nonmetals on the periodic table
  9. 16. charge particle
  10. 17. element name of a radioactive gas that can accumulate in houses
  11. 18. only element with atoms that do not have neturons
  12. 20. number number of protons in an atom
  13. 22. conducts heat well
  14. 23. a positively charged particle in the nucleus
  15. 25. Atomic number of fluorine (spelled out)
  16. 27. element used in balloons
  17. 28. Element 82