Chemistry Definitions Puzzle

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Across
  1. 4. An atom which has lost or gained electrons (3)
  2. 6. Number of Protons and neutrons (4/6)
  3. 9. A single part of a simple molecular substance, held together by weak intermolecular forces (8)
  4. 10. Has negligible mass (8)
  5. 13. Simplest ratio of atoms in a compound (9/7)
  6. 15. Mass of an atom relative to 1/12th the mass of a Carbon-12 atom (8/6/4)
  7. 18. Bonding type between a metal and a non metal (5)
  8. 19. Going Horizontally across the periodic table (6)
Down
  1. 1. Going Vertically down the periodic table (5)
  2. 2. Containing only one type of element or compound (4)
  3. 3. Actual number of atoms in a compound (9/7)
  4. 5. An atom with the same number of protons but a different number of neutrons (7)
  5. 7. Bonding type between two non metals (8)
  6. 8. Last subatomic particle to be discovered (7)
  7. 11. Containing more than one type of atom chemically bonded (8)
  8. 12. Model of the atom developed by JJ Thompson (4/7)
  9. 13. Containing only one type of atom (7)
  10. 14. Bonding type between metals (8)
  11. 16. Containing more than one type of element or compound not chemically bonded (7)
  12. 17. Has a charge of +1 (6)