Post on 26-Dec-2015
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
Particles of MatterParticles of Matter
• Protons: positively charged particles, found in the nucleus of an atom
• Neutrons: neutral particles found in the nucleus of an atom
Particles of MatterParticles of Matter
• Electrons: negatively charged particles occupying a region of space around the nucleus• 1/1860 the mass of a
proton
Particles of MatterParticles of Matter
• Elementary particles: these make up protons, neutrons, and electons• quarks are an example• not fully understood
Particles of MatterParticles of Matter
• atoms can combine:• molecules• formula units• chemical compounds
Particles of MatterParticles of Matter
• Ions: charged particles consisting of one or more atoms with a mismatch between the total numbers of protons and electrons
Particles of MatterParticles of Matter
• 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
Atomic MassAtomic Mass
• 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.
Atomic MassAtomic Mass
• 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
Gas PressureGas Pressure
• greater speed (kinetic energy) of atoms in the container → greater pressure
Gas PressureGas 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.
Kinetic TheoryKinetic Theory
• Liquids have particles in close association but with more mobility.
Kinetic TheoryKinetic Theory
• Cohesion: intermolecular attraction similar particles in a liquid have for each other
Kinetic TheoryKinetic Theory
• Adhesion: intermolecular attraction between particles of dissimilar materials
Kinetic TheoryKinetic Theory
• The kinetic theory of matter considers matter as a collection of numerous, extremely tiny particles in continuous motion.
Kinetic TheoryKinetic Theory
• Although the kinetic theory of matter has limitations, it does a good job predicting the behavior of matter under many conditions.
Kinetic TheoryKinetic Theory
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
TransitionsTransitions• Melting: from solid to liquid
• A solid’s molecules gain (absorb) enough kinetic energy to break out of their rigid arrangements and move more freely
TransitionsTransitions• Melting: from solid to liquid
• 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