states and changes of matter

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Across
  1. 2. formed through gaining or losing electrons to have 8 electrons
  2. 3. central
  3. 4. variants of a particular chemical element that have the same number of protons
  4. 7. chemical structure with an uneven distribution of electron density
  5. 9. group of chemical elements
  6. 10. chemical elements located on the upper right side of the periodic table
  7. 15. the number of protons found in the nucleus of an atom
  8. 16. symbolic representation of a substance's composition
  9. 17. negatively charged particles located in the outermost electron shell
Down
  1. 1. a link formed when two nonmetal atoms share pairs of valence electrons
  2. 5. visual representation of an atom's valence electrons
  3. 6. smallest unit of an element
  4. 8. only one type of atom
  5. 11. the smallest particle
  6. 12. positively charged metal ions and a shared sea of valence electrons
  7. 13. a class of chemical elements
  8. 14. when one atom transfers valence electrons to another