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Across 6. All atoms of the __________ element have the __________ number of protons in their nuclei. 9. The _______________ is a group of protons and usually neutrons. 10. Each kind of element has its own _______ (special) atomic number. For example, carbon is the only element with an atomic number of six. 13. ____________are particles in an atom that have a positive charge. 15. Only the element _________ has an atomic number of eight. 16. Electrons are particles in an atom that have a ______________ charge 18. Electrons move within a sphere-shaped region surrounding the nucleus. The presence of these negative electrons cause this area to have a ___________ charge. 23. The mass of protons and neutron is about ___________. 25. An elements is _____________ (named) by the number of protons in its nucleus. 26. ________________ are small particles of matter made of even smaller particles called protons, neutrons, and electrons. 28. Electrons move within a sphere-shaped region surrounding the nucleus. This region is called the electron ________ because electrons can be found anywhere within it. 29. _______________ are atoms of the same element (same number of protons) that have the different numbers of neutrons. 30. The number fourteen in ________ ___ represents the mass (sum of 7 protons and 7 neutrons) in an atom of this carbon isotope. 31. In 1897 J.J. ________ discovered electrons. His atom model had negative electron embedded in a positively charge sphere. 34. ( 3 words no spaces) Atoms are measured in units called _________ __________ _________. 36. In an _______ the number of positive protons and negative electrons is equal thus making the overall charge of an atom balanced or neutral 37. After J.J. Thompson, in 1911 ___________ created a model in which an atom was mostly empty space with electrons randomly orbiting around a small positive nucleus.

Down 1. ______________ are used to study objects or events too small, too large, too slow, too fast, too dangerous, or too far away to see. 2. Both a protons and a neutron have a mass of ______ amu. 3. The nucleus is the part of an atom that has a __________ charge due to the protons it contains. 4. In 1808, John ________ imagined that atoms as tiny, solid balls that had different mass for each kind of element 5. __________ is the abbreviation for atomic mass unit. 7. Electrons with low _______ move in the cloud close to the nucleus while electrons with higher amount of __________ move around the nucleus a a greater distance. 8. The _________ is the very small, very dense, center core of an atom. 11. ___________ are particles in an atom that have no (neutral) charge. 12. A ______ is a diagram, mental picture, a mathematical statement, or an object that helps explain ideas about the natural world. 14. Most of the size or _________ of atom is the space in which electrons move. 17. Each _______________ has a mass of about 1/2000 amu. 19. The size of the _________ is very tiny compared to the size (volume) of the electron cloud. 20. Models are used to help scientists make and test ____________ (educated guesses.) 21. The ___________ of an element may have different masses but they all react the same way chemically. 22. ___________ are particles that move rapidly around the outside of the nucleus. 24. (two words, no space) The ______________ is the number of protons in the atom oms of that element. 27. (two words, no space) The sum (added together) of the protons and neutrons in an atom is called the ____ ________. Hint-do not count the electrons because they weigh next to nothing. 32. The ________________ (amount of matter) of a electron is very small. It takes about 2000 electrons to equal the ___________ of one proton. 33. The ________ Model proposed that electrons move in specific layers and give off or absorb energy as they move from one "SHELL" to another. 35. Only the element ______ has an atomic number of twenty six.