2.1 Classifying matter: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
ElementsElementsSubstance 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
ElementsElementsExamples:
◦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
CompoundsCompoundsContains 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
MixturesMixtures2 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 Heterogeneous & Homogeneous MixturesMixturesHeterogeneous: 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 Solutions, Suspensions, and ColloidsColloids
Def: based on size of the largest
particlesSolution: 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
SuspensionsSuspensionsDef: 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
ColloidsColloids
1. Do not separate into layers
2. Cannot use a filter to separate
3. Scatters light
ie: fog, homogenized milk
2.2 Physical Properties2.2 Physical PropertiesDef: any characteristic observed
or measured without changing the composition of the substance(s)
Examples: viscosity, conductivity, malleability, hardness, melting point, boiling point, and density
ViscosityViscosity
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
ConductivityConductivity
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
MalleabilityMalleabilityDef: 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
HardnessHardness
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 Melting, Boiling, and DensityDensity
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 elementDensity: ratio of mass to volume
(g/cm3)◦Used to test purity of a substance
Separating MixturesSeparating MixturesFiltration: 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 2.3 Chemical PropertiesProperties
Def: ability to produce a change in the composition of matter◦observed when substances change
into different substances
Examples: flammability and
reactivity
Flammability and Flammability and ReactivityReactivity
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 Chemical & Physical ChangesChangesPhysical 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 Chemical versus Physical ChangeChange
Are different substances present
after?
◦Yes- chemical change
◦No- physical change
Examples?
3.1 Solids, Liquids, and 3.1 Solids, Liquids, and GasesGasesStates 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 StatesGases and Other StatesGases: 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 temperaturesBose-Einstein BEC: predicted by Einstein in the 1920s, accepted
in1995 -273oC, extremely low temperatures Groups of atoms behave as a single particle
Kinetic Theory:Kinetic Theory: Gases GasesDef: 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 & Kinetic Theory: Liquids & SolidsSolids
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 Changes3.3 Phase ChangesPhase 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 Energy and Phase ChangesChanges
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 FreezingMelting and FreezingMelting: 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 solidMolecules release energy and attractions between
particles have effect
◦Complete: particles vibrate in place
◦Solids at room temperature freeze at very high temps
VaporizationVaporizationDef: 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
CondensationCondensationDef: substance changes from gas or
vapor to liquid
◦Exothermic
◦i.e.: Fog on mirror, dew on grass