CHAPTER 2 PROPERTIES OF MATTER

1. CHAPTER 2PROPERTIES OF MATTER Chemists 6:45

2. PURE SUBSTANCES • Matter w/ same composition throughout • Table salt or sugar • Every pinch tastes equally salty/sweet • 2 categories: • Elements • compounds

3. ELEMENTS • substance that cannot be broken down into simpler substances. • fixed comp b/c it has only 1 type of atom • Cutting copper wire into smaller and smaller pieces until you end up with copper atoms • No 2 elements contain same type atom

4. EXAMPLES OF ELEMENTS At room temp (20°C, or 68°F), most solids, some gases, 2 liquids

5. SYMBOLS FOR ELEMENTS • 1813 - Jöns Berzelius (Swedish chemist) suggested symbols • 1 or 2 letters with 1st letter always CAPITALIZED • If 2 letters, 2nd letter not cap • Some Latin name of elements • Gold is Au (aurum) • Lead is Pb (plumbum)

6. COMPOUNDS • Substance made of 2 or more simpler substances • Can be broken down into simpler substances (elements or other cmpds) • Always joined in fixed proportion • H20 – 1 drop or 1 gallon, always 2 parts hydrogen for every 1 part oxygen • Silicon dioxide (clear crystals in sand) 1 pt silicon : 2 pts oxygen (di- means 2)

7. MIXTURES • Similar to cmpds b/c multiple substances • Different b/c properties can vary b/c composition NOT fixed • salsa – each bite has different amt of onion, pepper, etc • Pizza – each slice has diff amt toppings

8. HETEROGENEOUS MIXTURES • parts of mixture noticeably different from one another • Sand, trail mix, Lucky Charms, Italian salad dressing

9. How are the two brands of mixed nuts alike? How are they different? • What is the percent by mass of each type of nut? • Do the contents of each can meet the FDA regulations? Explain. • On the Brand A label, the nuts are listed in this order: peanuts, Brazil nuts, almonds, cashews, pecans, and hazelnuts. What do you think determines the order?

10. HOMOGENEOUS MIXTURES • Substances evenly distributed • difficult to distinguish one substance from another • Appears to contain only one substance • Stainless steel (iron, chromium, and nickel), Kool-Aid, and pool water

11. SOLUTIONS, SUSPENSIONS, AND COLLOIDS 3 major classifications of mixtures: Based on size of largest particles:

12. SOLUTIONS • small particles dissolved creating a homogeneous mixture • Windshield washer fluid, sweetened tea, Kool-Aid • Particles too small to settle out, be trapped by filter, or scatter light

13. SUSPENSIONS • Heterogeneous mixture separates into layers over time • Italian salad dressing, dirt particles in the air, quicksand • Large particles can be trapped by filter and scatter light making suspensions cloudy

14. COLLOIDS Matter Concept map • Intermediate size particles – larger than solution, smaller than suspension • Large enough to scatter light, too small to settle out / filtered • Milk, shaving cream, smoke, fog

15. PHYSICAL PROPERTIES SECTION 2.2

16. VISCOSITY resistance to flow High viscosity  slow flow high visc: – honey, lava, motor oil low visc: – water, vinegar, olive oil

17. CONDUCTIVITY measure of material’s ability to allow flow of heat / electricity Metals  high conductivity – called conductors Wood, rubber, and styrofoam low conductivity – poor conductors

18. MALLEABILITY Material’s ability to be hammered w/o shattering Most metals malleable ex. gold, lead, iron

19. HARDNESS Material’s resistance to be scratched Harder substances “scratch” softer ones Grinding wheels high $ b/c Contains diamond chips

20. MELTING & BOILING POINTS On p.47 Melting pt – solid to liquid Boiling pt – liquid to gas These characteristics can be used to separate substances out of mixtures

21. DENSITY Tests purity of substances Mass - volume ratio Methanol is fuel burned in some racing motorcycles. Must be 99.65% pure

22. USING PROPERTIES TO SEPARATE MIXTURES FILTRATION Separating materials based on size of particles brewing coffee iced tea

23. DISTILLATION When solution can’t be filtered, distillation used Distillation provides fresh water for submarines Fresh H2O and sea H2O separated b/c differences in boiling pts

24. RECOGNIZING PHYSICAL CHANGES Physical change – some properties of a material change, but substance remains same Ex. Melting ice cream, cut hair, crumple paper

25. CHEMICAL PROPERTIESSECTION 2.3

26. OBSERVING CHEMICAL PROPERTIES Candle burns causes hydrogen and carbon from paraffin to turn into carbon dioxide (new substance that was not originally present) Chemical properties observed only when substances are changing into different substances

27. FLAMMABILITY Burning in presence of OXYGEN Burning substances used as fuel Gasoline coal wood Sometimes not desirable Children’s sleepwear – low flammability Difficult to ignite Burns slowly

28. REACTIVITY When oxygen from air reacts with iron from car & water from air…..rust forms completely new substance……… Oxygen + water + iron = iron oxide (rust) Nitrogen is less reactive – N gas used in submarine tanks to replace reactive O gas

29. RECOGNIZING CHEMICAL CHANGES Look for: gas produced heat produced **change in color precipitate (solid) formed **Color change alone can also be physical change

30. IS A CHANGE CHEMICAL OR PHYSICAL? Color change as physical change…despite color change, iron is still iron Gas produced as physical change/…water boiling changes phases (liquid to gas) but still H2O

31. PHYSICAL V.S. CHEMICAL CHANGE When matter undergoes chemical change, comp of matter changes When matter undergoes physical change, comp remains same