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Across 1. The center of an atom; made up of protons and neutrons 4. A neutral subatomic particle in the nucleus of an atom. 7. The total number of protons and neutrons in the nucleus of an atom. 11. A chart that organizes information about all known elements according to their properties. 12. An atom that has gained or lost one or more elctrons. 13. A vertical column of elements in the periodic table. 15. An electron that may be found in the outermost energy level of an atom. 16. The number of protons in the nucleus of an atom. 17. A positively charged subatomic particle in the nucleus of an atom. 19. The elements that make up the zig-zag line and have properties of both metals and nonmetals. 20. The smallest unit of a compund that has all the properties of a compound.

Down 2. A substance that cannot be broken down into a simpler substance. 3. The elements located on the left of the zig-zag line and are good conductors of heat and electrictity. 5. Describes how an element reacts towards another element. 6. Any of the possible rings an atom may have. 8. A negatively charged subatomic particle found in the energy levels of an atom. 9. A horizontal row of elements in the periodic table. 10. The region around a nucleus of an atom where the electrons are located. 14. The elements located on the right side of the zig-zag line and are poor conductors of heat and electricity 18. The smallest particle that has properties of an element.