Chapter 2 Properties of Matter

Chapter 2Properties of Matter Chemists 6:45

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

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

Examples of elements • At room temp (20°C, or 68°F), most solids, some gases, 2 liquids

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)

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)

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

Heterogeneous Mixtures • parts of mixture noticeably different from one another • Sand, trail mix, Lucky Charms, Italian salad dressing

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?

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

Solutions, Suspensions, and Colloids • 3 major classifications of mixtures: • Based on size of largest particles:

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

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

Colloids • 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 Matter Concept map

Physical Properties Section 2.2

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

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

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

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

Melting & boiling points • Melting pt – solid to liquid • Boiling pt – liquid to gas • These characteristics can be used to separate substances out of mixtures On p.47

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

Using properties to separate mixtures • FILTRATION • Separating materials based on size of particles • brewing coffee • iced tea

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

Recognizing physical changes • Physical change – some properties of a material change, but substance remains same • Ex. Melting ice cream, cut hair, crumple paper

chemical Propertiessection 2.3

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

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

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

Recognizing chemical changes • Look for: • gas produced • heat produced • **change in color • precipitate (solid) formed • **Color change alone can also be physical change

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

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

Chapter 2 Properties of Matter