Chapter Two Key Terms

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Across 2. Number of protons in an atom's nucleus. 6. Type of waves with highest frequency and shortest wavelength. 9. Type of electrons in the outermost energy level of an atom. 11. Type of waves that travel at the speed of light through space. 12. Forms of the same element with different numbers of neutrons. 13. Type of waves that pass through soft body tissues but stopped by bones. 16. A way of illustrating valence electrons. 18. Greek philosopher who first coined the idea of the atom. 20. The space around the nucleus of an atom where electrons are found. 21. Last name of scientists who discovered electrons. 23. Type of waves that cause sunburn. 24. Last name of chemisty who gave us the law of definite proportions. 26. Last name of chemisty who gave us the law of conservation of matter. 27. Type of wave energy given off by the human body and other warm objects.

Down 1. The four basic elements of matter according to the ancient Greeks [no spaces between words]. 3. A fact of nature that is observed so often it is accepted as truth. 4. Positively charged subatomic particle. 5. Regions of space in which electrons can move about the nucleus. 7. The sum of protons and neutrons in an atom. 8. A testable prediction to explain an observation. 10. Waves transfer ____? 14. Waves with the lowest frequencies of the spectrum. 15. Part of the spectrum our eyes are sensitive to. 17. Small, dense, positively charged central core of an atom. 19. Last name of scientist who discovered the nucleus. 22. Neutral particle found in the nucleus of an atom. 25. An explanation based on many tests.

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