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Across 3. Atoms of the same _________ have the same amount of electrons in their outer shell. 7. Electrons are found in electron ______. 8. Rutherford’s version of the atom was comparable to the _______ ________. 12. __________ have the same atomic number but different mass number. 14. Chadwick discovered the _______. 15. The __________ has a mass of about 5.486 x 10^-4 amu. 17. Which atomic model did JJ Thomson make. 18. The outermost shell of an atom is the _________ shell. 19. An __________ atom has an electronic configuration of 2,6.

Down 1. Greek word the word atom came from. 2. ________ particles were shot at foil in the gold foil experiment. 4. Atoms of the same period have the same amount of electron ________. 5. The _________ charge of an atom is found in its nucleus. 6. The __________ __________ arranges atoms by increasing atomic number. 9. ________ is equal to the mass number – neutron number. 10. Who discovered the electron. 11. Argon-40 has 18 __________. 13. Charged atoms are __________. 14. 99% of an atom’s mass is found in its _________. 16. The mass number is also known as the __________ number.