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Across 1. Volume of space around a nucleus where electrons can be found most of the time. 5. One of two ions that result when a water molecule dissasociates: it has gained an electron and therefore is negative. 7. The ability of an atom to attract electrons toward itself in a chemical bond. 9. Chemical bond in which atoms share one pair of electrons. 10. Amount of heat energy required to raise the temperature of water 1 degree C. 11. One or two letters that represent the name of an element. 13. States that an atom other than hydrogen tends to form bonds until it has eight electrons in its outer shell. 15. Substance that can't be broken down into substances with different properties. 16. Atom of the same element having the same atomic number but a different mass number due to the number of nuetrons. 17. Hydrogen atom that has lost its electron and therefore bears a positive charge. 18. Chemical bond in which ions are attracted to one another by opposite charges. 23. Anything that takes up space and has mass. 24. Substance or group of substances that tend to resist pH changes of a solution. 25. type of molecule that does not interact with water because it is nonpolar. 28. Charged particle that carries a positive oir negative charge. 29. Mass of an atom equal to the number of protons plus the number of neutrons within the nucleus.

Down 2. Number of protons within the nucleus of the atom. 3. Concentric energy levels in which electrons orbit. 4. Union of two or more atoms of the same element:the smallest part of a compound that retains the properties of the compound. 6. Measurement scale for hydrogen ion concentration. 8. Weak bond that arises between a slightly positive hydrogen atom of one molecule and and a slightly negative atom of another molecule. 12. Molecules tending to lower the hydrogen ion concentration in a solution and raise the pH numerically. 14. Negative subatomic particle, moving about in an energy level around the nucleus of an atom. 17. Type of molecule that interacts with water by dissolving in water and/or forming hydrogen bonds with molecules. 19. Neutral subatomic particle, located in the nucleus and assigned one atomic mass unit. 20. Substance having two or more elements united chemically in a fixed ratio. 21. Molecules tending to raise the hydrogen ion concentration in a solution and lower its pH numerically. 22. Positive subatomic particle located in the nucleus and assigned one atomic mass unit. 26. Ionic compound that results from a classical acid-base reaction. 27. Smallest particle of an element that displays the properties of the element.