Elements and that

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Across
  1. 2. number of atoms in an element
  2. 4. A long molecule
  3. 6. The first word in Group zero's nickname
  4. 8. least reactive group one metal
  5. 9. lithium + ? --> lithium hydroxide + hydrogen
  6. 10. most reactive halogen
Down
  1. 1. The columns in the periodic table
  2. 3. The rows in the periodic table
  3. 5. Number of hydrogen atoms in methane
  4. 7. same number of these in an atom as the protons