Extra Credit Puzzle

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Across
  1. 3. Equal sharing of electrons
  2. 7. A substance undergoes a chemical reaction
  3. 12. Where all elements are found
  4. 17. In an Atom & has a neutral charge
  5. 18. Formed from a single atom
  6. 19. Substance combines with another to form a new substance
  7. 21. Atom loses valance electron and gains them from another
Down
  1. 1. Releases energy
  2. 2. Absorbs Heat
  3. 4. Measurement of how tightly packed together something is
  4. 5. One element replaces a similar element in a compound
  5. 6. Atoms of the same element with different #'s of neutrons
  6. 8. A mathematical sentence
  7. 9. A subatomic particle with a positive charge
  8. 10. The substances that go into a chemical reaction
  9. 11. Negatively charged Particle
  10. 13. The appearance changes but matter in substance doesn't
  11. 14. Gold,Copper,Tin
  12. 15. Process of rotting
  13. 16. Hydrogen,Oxygen,Carbon
  14. 20. Formed by chemical reactions