Periodic Crossword

123456789
Across
  1. 2. Horizontal rows on the Periodic Table.
  2. 4. Positively charged particles in an atom.
  3. 7. Positively charged center of an atom.
  4. 8. Vertical columns on the Periodic Table.
  5. 9. Negatively charged particles in an atom.
Down
  1. 1. Particles that differ in number between isotopes.
  2. 3. Atoms of the same element that have different masses.
  3. 5. Smallest known particle that makes up protons and neutrons.
  4. 6. The smallest form of matter that still retains the properties of an element.