Chapter 2: Properties of Matter Chemistry

2.1 Classifying matter: Composition: the combining of parts into a whole Pure substances: always have exactly the same composition Examples: table salt, sugar Uniform composition= samples have the same properties Can be classified into: elements and compounds

Elements Substance that can’t be broken into simpler substances ~100 exist Atom: smallest particle of an element Fixed composition: contains one type of atom Each element has a specific type of atom

Elements Examples: Symbols: Solids- aluminum, carbon Gases- oxygen, nitrogen Liquids- only 2 are liquid at room temperature [mercury and bromine] Symbols: 1813, Berzelius (Swedish chemist) One or two letters 1st capitalized and 2nd lower case Based on Latin names of elements i.e.: gold = Au or aurum Easy communication

Compounds Contains 2 or more elements joined in a fixed proportion 2 hydrogen to 1 oxygen = water Properties are different from the individual substances that they are made of ie: oxygen and hydrogen versus water

Mixtures 2 or more substances that are not chemically combined and can be separated Properties can vary: composition is NOT fixed Can retain properties of the substances being combined Classified by how well distributed the substances are in the mixture

Heterogeneous & Homogeneous Mixtures Heterogeneous: parts of a mixture are noticeably different from one another ie: sand, salad “hetero” = different; “genus” = kind Homogeneous: substances are distributed evenly & it’s hard to tell one from another Appears to be made of one substance ie: water in a swimming pool, stainless steel

Solutions, Suspensions, and Colloids Def: based on size of the largest particles Solution: when substances dissolve and form a homogeneous mixture ie: tap water, windshield wiper fluid 1. Do not separate into layers over time 2. Cannot filter to separate 3. Allows light to pass through

Suspensions Def: a heterogeneous mixture that separates into layers over time “Shake well before using” ie: sand in water 1. Can be filtered to separate 2. Appear “cloudy” 3. Scatter light in all directions

Colloids 1. Do not separate into layers 2. Cannot use a filter to separate 3. Scatters light ie: fog, homogenized milk

2.2 Physical Properties Def: any characteristic observed or measured without changing the composition of the substance(s) Examples: viscosity, conductivity, malleability, hardness, melting point, boiling point, and density

Viscosity Def: a liquid’s resistance to flowing Greater viscosity = slower the liquid flows Lower viscosity = faster the liquid flows Honey is more viscous than water Usually decreases when heated (thins out) ie: Motor oil has to have the correct viscosity in different temperatures

Conductivity Def: a material’s ability to allow heat to flow Conductors: have high conductivity Metals Usually a good conductor of electricity Insulators: have low conductivity Woods Usually a bad conductor of electricity

Malleability Def: ability of a solid to be hammered without shattering Most metals (gold) are very malleable Ice and glass are not very malleable Brittle: solids that shatter when struck

Hardness Def: how hard a solid is Compare by scratching one material on another Kitchen knife against copper sheet Diamond is the hardest known material

Melting, Boiling, and Density Melting and boiling points: Melting point- temp at which substance changes from solid to liquid Boiling point- the temp at which substance changes from liquid to vapor Specific to each compound or element Density: ratio of mass to volume (g/cm3) Used to test purity of a substance

Separating Mixtures Filtration: separates materials based on size of particles ie: coffee filters, wire screen Distillation: separates substances in a solution by boiling point i.e.: fresh water for submarines

2.3 Chemical Properties Def: ability to produce a change in the composition of matter observed when substances change into different substances Examples: flammability and reactivity

Flammability and Reactivity Flammability: material’s ability to burn in the presence of oxygen ie: gasolines, fabrics, drywall Reactivity: how readily a substance combines chemically with other substances oxygen with iron and water = rust nitrogen gas can be used to slow rust production

Chemical & Physical Changes Physical Change: properties change, but substances stay the same ie: phase changes, slicing foods, crumpling paper Most can be reversed, but not all Chemical change: substance reacts and forms one or more new substances ie: baking/cooking, food digesting 1. Unexpected change in color 2. Production of a gas 3. Formation of a precipitate

Chemical versus Physical Change Are different substances present after? Yes- chemical change No- physical change Examples?

Chapter 3: States of Matter

3.1 Solids, Liquids, and Gases States of Matter: classified based on whether shapes and volumes are definite or variable Solids: definite shape & definite volume ie: pencil, desk, chalkboard Orderly arrangement of particles at atomic level Liquids: take shape of container & definite volume ie: water at room temp, pop, juice Slightly random arrangement of particles at atomic level

Gases and Other States Gases: no definite shape and no definite volume ie: helium, “air,” natural gas Takes the shape and volume of its container Random arrangement of particles at the atomic level volume: can be compressed or expanded Plasma: 99% of all observable matter Extremely high temperatures Bose-Einstein BEC: predicted by Einstein in the 1920s, accepted in1995 -273oC, extremely low temperatures Groups of atoms behave as a single particle

Kinetic Theory: Gases Def: all particles of matter are in constant motion Kinetic energy: energy an object has due to motion Gases: constant motion allows gases to fill containers of any size/shape Constant, random motion Motion of particles unaffected by other particles (unless in collision) Forces of attraction among particles can be ignored most of the time

Kinetic Theory: Liquids & Solids Liquids: particles have motion slower than gases & faster than solids Particles flow to new locations & take shape of container Volume constant because forces of attraction keep particles close together ie: students moving through crowded hallways, airports Solids: particles have “slowest” motion, vibration Definite shape and volume Particles vibrate around fixed locations ie: people in a movie theater, in a car on a road trip

3.3 Phase Changes Phase change: reversible, occurs when a substance changes from one state to another Common phase changes: melting, freezing, vaporization, condensation, sublimation, and deposition Temperature: the temp of a substance does not change during a phase change Phase change graphs Melting point = freezing point Boiling point = condensation point

Energy and Phase Changes Energy is absorbed or released during a phase change Endothermic: system absorbs energy ie: ice melting Exothermic: system releases energy i.e.: water freezing into ice

Melting and Freezing Melting: endothermic; going from solid to liquid Molecules gain energy to overcome attractions between particles Complete: all particles have enough energy to “flow” Freezing: exothermic; going from liquid to solid Molecules release energy and attractions between particles have effect Complete: particles vibrate in place Solids at room temperature freeze at very high temps

Vaporization Def: substance changes from liquid to gas, endothermic Evaporation: liquid gas at temps below the boiling point Takes place at the surface of a liquid Vapor- gas phase of a substance that is usually solid or liquid at room temp Vapor pressure- caused by collisions of vapor and walls of a container Boiling: vapor pressure becomes = to atmospheric pressure Molecules below surface have kinetic energy to overcome particle attractions Bubbles quickly rise to the surface & burst

Condensation Def: substance changes from gas or vapor to liquid Exothermic i.e.: Fog on mirror, dew on grass

Sublimation and Deposition Sublimation: substance changes from solid to gas or vapor without changing to a liquid 1st Endothermic ie: dry ice Deposition: gas or vapor changes directly into solid without 1st changing to a liquid Exothermic ie: frost on windows