elements and periodic table

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Across
  1. 2. This element is a noble gas with the symbol "He".
  2. 3. Table The name of the table that organizes all known elements.
  3. 5. The positively charged particle in the nucleus.
  4. 7. The scientist who created the first periodic table.
  5. 10. Elements in the same group have similar __________ properties.
  6. 12. This element has the symbol "O".
  7. 13. This element has the symbol "Na".
Down
  1. 1. A negatively charged particle that orbits the nucleus.
  2. 3. The atomic number represents the number of these in the nucleus.
  3. 4. Mass The average mass of all the isotopes of an element.
  4. 6. A horizontal row on the periodic table.
  5. 8. The central part of an atom, containing protons and neutrons.
  6. 9. A vertical column on the periodic table.
  7. 11. The smallest unit of matter that retains the properties of an element.