Chemistry| the periodic table

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Across
  1. 3. known as inert gases, elements known for their stability
  2. 4. the regions surrounding the nucleus where electrons may be found
  3. 7. A list of all known elements arranged in order of increasing atomic number
  4. 9. Centre of an atom, made of protons and neutrons
Down
  1. 1. rows on the periodic table
  2. 2. Number of particles in the nucleus
  3. 5. Horizontal rows on the periodic table
  4. 6. Forms of the same element that have different molecular structures and therefore different properties
  5. 8. substance composed of atoms with the same atomic number (118 are known to exist)