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Across 4. Symbolic representation of the number and type of atoms of elements ina compound 5. Matter with a fixed volume which takes the shape of its container 8. Represents species involved in a chemical reaction 10. Starting substance in a chemical change or reaction 11. Forms of an element with the same number of protons but a different number of neutrons in the nuclei 12. Number of protons in the nucleus of an atom; an indicator of the placement of an element on the periodic table 15. Chemical reaction which releases energy 19. Substance produced by a chemical change or reaction 20. Two or more substances combined with no fixed ratio 21. A 'pure' substance that consists of one type of atom 22. The name given to force holding atoms together in a compound

Down 1. State of matter in which particles have fixed positions resulting in a definitive volume; particles show vibration motion only 2. A neutral particle found in the nucleus of an atom, of approximately the same size and mass as a proton 3. Two or more particles (atoms) chemically combined 6. The total of the number of protons and neutrons in an atom 7. Matter which takes the shape and occupies the volume of its container 9. Chemical reaction that absorbs energy 13. Two or more elements combined chemically in a fixed, whole-number ratio 14. Mass per unit volume 15. Small negatively charged subatomic particle that moves rapidly around the atom's nucleus 16. The colection of protons and neutrons in the centre of an atom 17. Smallest particle of matter that cannot be divided by chemical or physical means 18. Positively charged particle in the nucleus of an atom