Complete the crossword, then click on "Check" to check your answer. If you are stuck, you can click on "Hint" to get a free letter. Click on a number in the grid to see the clue or clues for that number.

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Across: 3. The arrangement of elements according to increasing atomic number. 4. The number of protons in the nucleus of an atom. 5. A chemical reaction that absorbs heat. 7. A chemical reaction that releases heat. 8. 2 or more substances that are physically combined. No chemical bonding occured between the substances. 9. The number of protons and neutrons in the nucleus of an atom. 12. The smallest piece of a compound. 13. The smallest unit of an element. The basic unit of matter. 14. Smallest part of an atom. It has a negative charge and is the only part involved in bonding. 15. Change in matter that only alters the size, shape, or form. No chemical bonds are changed.

Down: 1. A substance made of 2 or more elements joined by bonds in a fixed ratio. 2. A chemical bond that is formed when electrons are shared between 2 atoms. 6. A chemical bond formed by the attraction of 2 oppositely charged ions. 10. This type of change involves making/breaking of bonds to form a new type of matter. 11. A pure substance made of only 1 type of atom.