matter

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Across
  1. 4. the number of protons and neutrons in a nucleus
  2. 7. a substance that can not be broken down into simpler substances
  3. 8. an atom that gains or losses one or more eletrons in its outermost energy level has a net electric charge
  4. 9. atoms in the same element that have different mass numbers
Down
  1. 1. the number of protons in a nucleus
  2. 2. the center of an atom
  3. 3. a tiny particle that has mass and has an electric charge
  4. 4. anything that has volume and mass
  5. 5. it has a negative charge at the same magnitude as the proton
  6. 6. a tiny particle with the same mass as a proton but has no electrical charge