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Across 3. there are seven __________ (rows) and 18 columns or groups of elements on the Periodic Table (Fact 259) 5. ______________ or life science is the study of living things (Fact 154) 8. living things are made of the elements carbon, hydrogen, nitrogen, phosphorus, and _______ (Fact 274) 13. all chemical reactions involve thermal energy being absorbed (___________) or released (exothermic) (Fact 271) 15. the two types of carbohydrates are __________and and sugars (Fact 278) 19. human beings have _____ ______ pairs of chromosomes (Fact 183) 20. ___________ is the study of Earth's atmosphere (Fact 81) 21. proteins re made of smaller particles called ______ ______ (Fact 280) 22. ______________ are organic compounds made by living things (Fact 275) 24. a _______ ________ is a force of attraction that holds two or more atoms together due to the rearrangement of electrons between them (Fact 266) 25. compounds can be broken down into the elements that for them through _______ ___________ (Fact 264) 26. __________ are organic compounds that make up parts of cell membranes and other organelles (Fact 279)

Down 1. the main organ of the excretory system is the ________; it functions to eliminate wastes from the bloodstream and the body (Fact197) 2. _______ is the study of the physical structure of Earth, its history, and the forces that shape it (Fact 79) 4. A/an ________ is a pure substance (made of identical particles) made of two or more elements chemically combined (Fact 262) 6. _________ is the hereditary material in humans and in almost all other organisms (Fact 171) 7. ___________ is the study of matter, energy, motion, and forces (Fact 219) 9. the starting substances in a chemical reaction are called __________ (Fact 268) 10. almost all organic compounds contain the element ________ (Fact 272) 11. the law of __________ of mass (matter) states that mass is not created or destroyed during ordinary physical or chemical changes (Fact 270) 12. the new substances formed in a chemical reaction are called __________ (Fact 269) 14. elements can be classified into three categories, metals, __________, or metalloids (semi-metals) (Fact 255) 16. ____________ are organic compounds used by organisms as an energy source and energy storage (Fact 277) 17. carbon is the backbone of organic compounds because it can form four _____ _______ with itself and with atoms of other elements (Fact 273) 18. _________ is the study of the properties and interactions of matter (Fact 219) 23. A/an ___________ is a pure substance (made of identical particles) tht cannot be broken down into simpler substances by physical or chemical means (Fact 253)