Crossword Puzzle

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Across
  1. 3. The polyatomic ion HCO₃⁻
  2. 6. Electrons in the outermost energy level
  3. 8. positively charged ion
  4. 9. Number of electrons in Sr²⁺
Down
  1. 1. A number placed in front of a chemical formula
  2. 2. An element in Group 17 of the periodic table
  3. 4. GAS An element in Group 18 that is generally unreactive
  4. 5. negatively charged ion
  5. 7. The distance from the center of an atom to its outer edge
  6. 10. Number of oxygen atoms in Ca(HCO₃)₂