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Across 3. the total number of protons and neutrons in a nucleus 5. An electron in one of the outer shells of an atom that can participate in forming chemical bonds with other atoms 7. a table of the chemical elements arranged in order of atomic number 10. an element whose properties are intermediate between those of metals and solid nonmetals 11. a stable subatomic particle with a positive electric charge 12. the mass of an atom of a chemical element 13. the central and most important part of an object 14. a stable subatomic particle with a charge of negative electricity 15. the number of protons in the nucleus of an atom 16. a solid material that is typically hard, shiny, malleable, fusible, and ductile

Down 1. the basic unit of a chemical element 2. each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nucleus 4. where electrons are when they go around the nucleus of an atom 6. a number of people or things that are located close together or are considered or classed together 8. a subatomic particle of about the same mass as a proton but without an electric charge 9. an element not having the character of a metal