Carter's Puzzizle

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Across
  1. 2. Low temperature
  2. 4. State of matter that fills space
  3. 7. State of matter with fixed shape
  4. 8. When something becomes different
  5. 10. H20 liquid we drink
  6. 14. Substance with pH above 7
  7. 16. Process where New substance is formed
  8. 19. White solid used in food
  9. 21. State of matter that flows
Down
  1. 1. Center of an atom
  2. 3. Mass per unit volume
  3. 5. Substance with pH below 7
  4. 6. Outer electrons used in bonding
  5. 9. Pure substance made of one type of atom
  6. 11. Energy that makes things warmer
  7. 12. Row on the periodic table
  8. 13. Basic unit of matter
  9. 15. Amount of matter in an object
  10. 17. Combine two things together
  11. 18. Sweet substance
  12. 20. Mixture of gases we breathe