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Across
  1. 3. Neutral particle in nucleus
  2. 7. Lightest element
  3. 9. Element found in all life forms
  4. 11. Ionized gas state
  5. 13. Major gas in Earth’s atmosphere
  6. 15. Substance made of two or more elements
  7. 16. State of matter with no fixed volume
  8. 18. Pure substance made of one kind of atom
  9. 20. Physical blend of substances
  10. 21. Arrangement of elements by properties
  11. 23. Atom with a charge
  12. 24. State of matter with definite shape
Down
  1. 1. Light noble gas
  2. 2. Ability to do work
  3. 4. Gas essential for respiration
  4. 5. Force holding atoms together
  5. 6. Positively charged particle in nucleus
  6. 8. Same element, different number of neutrons
  7. 10. Process that changes substances
  8. 12. Repeating pattern in elements
  9. 14. Two or more atoms bonded together
  10. 17. Smallest unit of an element
  11. 19. Negatively charged particle
  12. 22. State of matter with fixed volume
  13. 24. One- or two-letter code for an element