Theories of Matter. usually rigid, having definite shape and volume Solids.

Theories of MatterTheories of Matter

• usually rigid, having definite shape and volume

SolidsSolids

• definite volume• assume shape of

containers but may not fill them

• can flow under influence of force

LiquidsLiquids

• low density• can flow• can completely fill its

container• easily compressed and

rarified

GasesGases

• exist when the particles of matter have enough kinetic energy that at least some of their electrons become stripped away

• very high temperatures

PlasmasPlasmas

• fluid-like, as gases or liquids

• consist of a neutral mixture of electrons and positively charged particles

PlasmasPlasmas

• solids, liquids, and gases have been understood for centuries

• states of matter are difficult to define with precision

States of MatterStates of Matter

• Elements: the basic chemical building blocks of matter

• cannot be broken down into simpler substances by ordinary means

Particles of MatterParticles of Matter

• John Dalton developed atomic theory—matter is made up of atoms

• now know that atoms can be subdivided


• Protons: positively charged particles, found in the nucleus of an atom

• Neutrons: neutral particles found in the nucleus of an atom


• Electrons: negatively charged particles occupying a region of space around the nucleus• 1/1860 the mass of a

proton


• Elementary particles: these make up protons, neutrons, and electons• quarks are an example• not fully understood


• atoms can combine:• molecules• formula units• chemical compounds


• Ions: charged particles consisting of one or more atoms with a mismatch between the total numbers of protons and electrons


• inconvenient to measure in grams or kilograms

• relative mass unit• atomic mass unit (amu)• unified atomic mass unit (u)

Atomic MassAtomic Mass

• Mole: amount of a substance containing 6.022 × 1023 particles

• Avogadro’s constant (NA) or Avogadro’s number


• A carbon-12 atom has a mass of 12.00 u. Avogadro’s number of carbon-12 atoms will have a mass of 12.00 g.


• Ideal gas model is a good illustration of the kinetic theory

• Pressure = sum of impulsive forces divided by area of sides

Gas PressureGas Pressure

• more atoms in the container → greater pressure

• smaller “area” on which to exert force → greater pressure


• greater speed (kinetic energy) of atoms in the container → greater pressure


F =F =ΔtΔt

2mv2mv

• The particles in solids are held rigidly with strong intermolecular force.

• These particles can vibrate in place.

Kinetic TheoryKinetic Theory

• The velocity of these vibrations determines the particles’ kinetic energy.

• Large amounts of kinetic energy are indicated with high temperatures.


• Liquids have particles in close association but with more mobility.


• Cohesion: intermolecular attraction similar particles in a liquid have for each other


• Adhesion: intermolecular attraction between particles of dissimilar materials


• The kinetic theory of matter considers matter as a collection of numerous, extremely tiny particles in continuous motion.


• Although the kinetic theory of matter has limitations, it does a good job predicting the behavior of matter under many conditions.


States of MatterStates of Matter

ArrangementArrangement• Crystalline solids: particles

are held in fixed patterns• unit cell• NaCl is a good example• most metals

ArrangementArrangement• Amorphous solids:

particles do not form repeating patterns• glass

• Heterogeneous solids: have combination of crystalline and amorphous solids

Elastic ModulusElastic Modulus• Solids can change shape

in response to certain forces

• Tensile forces tend to pull apart

Elastic ModulusElastic Modulus• Stress (σ): related to the

tension force normal (perpendicular) to the cross-sectional area

• Defined: force per unit area

σ =AF

Elastic ModulusElastic Modulus• Strain (ε): amount

stretched (Δl) divided by the initial length (li)

• usually expressed as a simple decimal or percent

ε =li

Δl

Elastic ModulusElastic Modulus• Elastic modulus (E): ratio

of the normal stress to the linear strain

• units: N/m²• plural: elastic moduli

E =εσ

Elastic ModulusElastic Modulus• determined experimentally

and listed in tables for various substances

• measure of a material’s resistance to change in shape (stiffness)

Elastic ModulusElastic Modulus• If a wire’s elastic modulus,

cross-sectional area, initial length, and the tension exerted on it are known, the change in length can be estimated:

Δl =AEF·li

ForcesForces• Compressive forces: crush

or push particles of matter together

• Shearing forces: tend to cause layers of particles within the solid to slide parallel to each other

Shear ModulusShear Modulus• Shear stress equals the

force exerted parallel to the surface, divided by the surface area.

• Shear strain is the ratio of deformation of the object parallel to the force, divided by the separation of the two surfaces.

• Shear modulus (G) is the ratio of shear stress to shear strain:

G =shear stressshear strain

Stress-Strain GraphStress-Strain Graph

Stress-Strain GraphStress-Strain Graph• Proportional limit:

maximum strain without permanent deformation

Stress-Strain GraphStress-Strain Graph• Elastic limit: limit of

reversible deformation

Stress-Strain GraphStress-Strain Graph• At the fracture point, the

object breaks.

Stress-Strain GraphStress-Strain Graph• Materials work harden

when stress is applied in a cyclic way, causing them to become harder or more brittle.

• This changes the stress-deformation curve.

TransitionsTransitions• Melting: from solid to liquid

• The melting point is usually a predictable temperature at which this occurs


• A solid’s molecules gain (absorb) enough kinetic energy to break out of their rigid arrangements and move more freely


• The melting point of a solid also depends on the pressure

• Water has unusual properties

TransitionsTransitions• Water expands when it

freezes.• higher pressures hinder

freezing• Regelation: melting under

pressure

FluidsFluids• Liquids and gases are

both classified as fluids.• no fixed shape• assume the shape of

their containers• can flow under the

influence of a force

Surface TensionSurface Tension• Cohesion at the surface of

a liquid pulls the molecules at the surface toward the interior.• The net force is inward.• This is especially

evident with polar molecules like water.

Surface TensionSurface Tension• explains why water forms

into droplets• meniscus• overflow a glass with

water

AdhesionAdhesion• a liquid’s surface

molecules may be more attracted to an adjoining surface than to each other

• capillarity• liquids flowing into fibrous

and porous materials

GasGas• particles are very energetic

and widely separated• most gases are elements or

molecular compounds

VaporizationVaporization• a change of state from solid

or liquid to gas• Sublimation: directly

from solid to gas• Boiling: characterized by

rapid formation of vapor bubbles within a liquid

VaporizationVaporization• a change of state from solid

or liquid to gas• Evaporation: vaporization

of a liquid below the boiling point and above the freezing point of the liquid

EvaporizationEvaporization• occurs only at the natural

surface of a liquid• primary means water uses

to return to the atmosphere• liquids cool as they

evaporate

EvaporizationEvaporization• in a closed container, a

dynamic equilibrium may be reached• molecules entering

gaseous phase equal in number to those entering liquid phase

EvaporizationEvaporization• in a closed container, a

dynamic equilibrium may be reached• vapor pressure: pressure

of the gas when the closed system has reached equilibrium

Vapor PressureVapor Pressure• depends on the kind of

liquid and its temperature• volatile liquids have low

cohesive forces with high vapor pressures

Vapor PressureVapor Pressure• nonvolatile liquids tend to

have lower vapor pressure at a given temperature

• nonvolatile liquids tend to have lower vapor pressure at a given temperature

• nonvolatile liquids tend to have lower vapor pressure at a given temperature

CondensationCondensation• vapor goes from the

gaseous state to liquid• depends on multiple factors

SolidificationSolidification• phase transition from liquid

to solid• also called freezing• freezing and melting points

are almost always the same for a pure substance

SolidificationSolidification• gases can enter the solid

phase• deposition• depends on temperature

and other factors

Phase DiagramsPhase Diagrams• shows relationships among

phases of a substance compared to controlling factors such as pressure and temperature

Phase DiagramsPhase Diagrams• Triple point: the

combination of temperature and pressure where all three phases of a substance can coexist

• water: 0.01°C and 0.006 atm

Theories of Matter. usually rigid, having definite shape and volume Solids.

Documents

Transcript of Theories of Matter. usually rigid, having definite shape and volume Solids.