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Across 3. A substance that cannot be chemically interconverted or broken down 5. When two elements or substances are put together to form another substance 6. The positively charged central core of an atom 7. Positively charged ion 10. Negative charged ion 11. Contain equal numbers of protons but different numbers of neutrons

Down 1. An subatomic particale with a neutral charge 2. The mass of an atom of a chemical element expressed in atomic mass units ; Normally a decimal (2 Words) 4. A subatomic particle occurring in all elements, with a positive electric charge 8. The vertical section of periodic table 9. The horizontal row on a periodic table 10. Smallest form of matter