Atomic structure/periodic table crossword puzzle

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Across
  1. 3. building block of subatomic particles
  2. 4. particles with an electric charge of 1-
  3. 5. a single electron or one of two or more electrons in the outer shell of an atom
  4. 7. weighted-average mass of the mixture of its isotopes
  5. 8. particles with an electric charge of 1+
  6. 10. elements arranged by increasing atomic number and by changes in physical and chemical proporties
  7. 12. the horizontal rows of elements on the periodic table
  8. 13. smallest building block of all matter
Down
  1. 1. neutral particles that do not have an electrical charge
  2. 2. Positively-charged center of the atom
  3. 4. the area around the nucleus of an atom where its electrons are most likely found
  4. 6. an element or substance that is not a metal
  5. 7. the number of protons in an atom
  6. 9. the salt form of an element
  7. 11. Atoms of the same element that have different numbers of neutrons