Unit crossword puzzle

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Across
  1. 5. is the law of mass
  2. 6. are on the outer levels of a atom
  3. 7. start before a chemical reaction
  4. 10. result from a chemical reaction
Down
  1. 1. end after chemical reaction
  2. 2. is the positive part of the nucleus
  3. 3. are the negative part of the nucleus
  4. 4. does not create new substances
  5. 8. is the horizontal rows in a periodic table
  6. 9. are the vertical columns in a periodic table