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Across 1. the new substances formed in a chemical reaction are called __________ (Fact 269) 3. _______ is the study of the physical structure of Earth, its history, and the forces that shape it (Fact 79) 5. A/an ________ is a pure substance (made of identical particles) made of two or more elements chemically combined (Fact 262) 8. there are seven __________ (rows) and 18 columns or groups of elements on the Periodic Table (Fact 259) 10. __________ are organic compounds that make up parts of cell membranes and other organelles (Fact 279) 13. ______________ are organic compounds made by living things (Fact 275) 14. _________ is the hereditary material in humans and in almost all other organisms (Fact 171) 15. compounds can be broken down into the elements that for them through _______ ___________ (Fact 264) 18. ______________ or life science is the study of living things (Fact 154) 19. elements can be classified into three categories, metals, __________, or metalloids (semi-metals) (Fact 255) 22. _________ is the study of the properties and interactions of matter (Fact 219) 23. a _______ ________ is a force of attraction that holds two or more atoms together due to the rearrangement of electrons between them (Fact 266) 24. ___________ is the study of matter, energy, motion, and forces (Fact 219) 25. the law of __________ of mass (matter) states that mass is not created or destroyed during ordinary physical or chemical changes (Fact 270)

Down 2. human beings have _____ ______ pairs of chromosomes (Fact 183) 4. all chemical reactions involve thermal energy being absorbed (___________) or released (exothermic) (Fact 271) 5. almost all organic compounds contain the element ________ (Fact 272) 6. the main organ of the excretory system is the ________; it functions to eliminate wastes from the bloodstream and the body (Fact197) 7. carbon is the backbone of organic compounds because it can form four _____ _______ with itself and with atoms of other elements (Fact 273) 9. living things are made of the elements carbon, hydrogen, nitrogen, phosphorus, and _______ (Fact 274) 11. the starting substances in a chemical reaction are called __________ (Fact 268) 12. ___________ is the study of Earth's atmosphere (Fact 81) 16. ____________ are organic compounds used by organisms as an energy source and energy storage (Fact 277) 17. proteins re made of smaller particles called ______ ______ (Fact 280) 20. 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) 21. the two types of carbohydrates are __________and and sugars (Fact 278)