Science assignment

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Across
  1. 2. Catalyst involved in chemical reactions in living things
  2. 5. Mass of one atom of an element calculated from the total number of protons neutrons and electrons of that atom
  3. 8. A reaction that takes place when two or more substances react to from a new substance
  4. 12. Pure substance that cannot be broken down into other substances
  5. 13. A neutral substance is neither an acid nor a base
  6. 14. Atom that has become electrically charged because it has lost or gained electrons
  7. 15. substance that helps a chemical reaction to proceed more quickly
  8. 16. An experiment in which all reactants and all products of a chemical reaction are accounted for
  9. 19. Positively charged center of an atom that contains protons and neutrons
  10. 20. Chemical reaction that releases energy
  11. 22. Number of protons in the nucleus of one atom of an element
Down
  1. 1. dull, brittle element that does not conduct electricity
  2. 3. A table in which the elements are organized by their physical and chemical properties
  3. 4. Chemical reation that occurs when oxygen reacts with a substance to from an new substance and give off energy
  4. 6. A chemical reaction that absorbs energy
  5. 7. Group 18 elements in the periodic table of elements that is most stable and unreactive elements
  6. 8. Principle that matter is not created or destroyed in a chemical reaction
  7. 9. Change that results when two or more substances react to create a different substance or substances
  8. 10. An experiment in which one or more products of a chemical reaction can escape
  9. 11. Group 17 elements in the periodic table, the most reactive non-metals
  10. 16. Slow chemical change occurs when oxygen in the air reacts with metal
  11. 17. invisible negatively charged particle that orbits the nucleus o an atom
  12. 18. Element that has both metallic and non-metallic properties
  13. 21. Chemical combination of two or more elements in a specific ratio
  14. 23. shiny, malleable, ductile, elements that conduct electricity
  15. 24. Substance that reacts with another substance or substances in a chemical reaction to create new substances with other substances