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Across 1. atoms have same atomic number but different number of neutrons. 4. 1/12 the mass of a carbon atom. (4 Words) 5. The number of protons in the nucleus of an atom. (2 Words) 7. a horizontal row of the periodic table. 8. neutral subatomic particle in the nucleus of an atom. 9. Greek philosopher who was among the first to suggest the existence of atoms. 12. elements that lose electrons and form cations.(negatively charged. 14. English chemist and science teacher who formulated a theory to describe the structure and reactivity of matter in terms of atoms. (2 Words) 15. equals the number of neutrons plus the number of protons in the nucleus of an atom. (2 Words) 17. an arrangement of elements according to similarities of an element. (2 Words) 19. negatively charged subatomic particle. 21. a group of ions that participates like a single ion. (2 Words) 22. elements that gain electrons and result in to anion (positively charged) 23. a vertical column of elements in the periodic table 24. stream of electrons produced at the negative electrode of a tube containing a gas at low pressure. (2 Words)

Down 2. an instrument used to generate images of individual atoms. (4 Words) 3. the central core of an atom, which is composed of protons and neutrons. 6. charged atoms 10. positively charged atom when an atom gains an electron is called. 11. particle which determines the identity of an isotope 13. negatively charged atom when an atom loses an electron. 16. weighted average mass of the atoms in a naturally occuring sample of an element (2 Words) 18. matter is composed of 4 things. 20. the smallest particle of an element that retains its identity. 21. positively charged subatomic particle in the nucleus of an atom.