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Across 3. a negatively charged particle 6. credited with the earliest idea of atoms existing. He was a Greek philosopher. 8. an electrically nuetral group of atoms that act as a single unit 10. smallest particle of an element that retains the chemical properties of that element 12. number of protons in the nucleus of an atom, which determines the chemical properties of an element and its place in the periodic table. (2 Words) 14. when atoms or ions join together to form new substances 15. metals + nonmetals = ? (2 Words) 16. atoms that have a positive or negative charge 17. a positively charged particle

Down 1. nonmetals + nonmetals = ? (2 Words) 2. credited with the "planetary" model of the atom that shows electrons orbiting the nucleus 4. discovered the nucleus 5. a small region located in the center of an atom 7. credited with the development of an early atomic theory 9. credited with the discovery of the nuetron 11. a particle with no charge 13. credited with the discovery of the electron and the "plum pudding" model of the atom