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Across 2. an isotope of this element with a mass number of 25 has 13 neutrons 5. original 4 elements were air, earth, fire and __________ 8. an isotope of this element with a mass number of 87 has 37 protons 9. a pure substance made up of more than one kind of atom is called a ______ 11. of the elements uranium, plutonium, bismuth and selenium, which one is artificially produced? 12. cobalt-60 is used in the treatment of 19. an element which has 7 electrons in its highest orbit and is liquid at room temperature 20. wrote the "Skeptical Chymist" 21. Of the elements carbon, nitrogen, oxygen or fluorine, which one has 5 electrons in its highest filled shell? 24. an isotope of this element with a mass number of 39 has 19 neutrons 26. came up with the first useable periodic table 28. neutral ____ has 74 electrons 31. decomposed mercuric oxide into its elements 33. a vertical column of the periodic table is called a chemical ___ 35. the name of an isotope with 1 proton and 1 neutron 36. when an alkali metal reacts with water it produces ___ gas

Down 1. the most reactive halogen is 3. the number of protons is called the ___number 4. a colourless, non-reactive element used in light bulbs and welding aluminum is 6. Cavendish burned hydrogen in pure _____ to produce water. 7. a group of atoms joined together 10. the ____'s stone could change lead into gold 13. an element with an atomic mass of 112.4 14. an isotope with an unstable nucleus is said to be 15. first came up with the idea of atoms 16. he explained the spectrum of hydrogen using his model of the atom 17. a non-reactive element used in airships 18. an element used to disinfect water in pools and drinking water. 19. isolated phosphorus from urine 22. kept the 4 element hypothesis alive for 2000 years 23. an element with 52 protons 25. the third orbit in an atom of potassium contains how many electrons? 27. first suggested matter is made of 4 elements 29. an element which has similar properties to sodium, but has a smaller atomic mass is 30. different forms of the same kind of atom with different numbers of neutrons are called 32. published the Atomic Theory 34. for sodium to have the stable electron arrangement of a noble gas, it would have to ___ an electron