chem exam 3 flashcards

8/14/2019 Chem Exam 3 Flashcards

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Tro, Chemistry: A Molecular Approach 1

Potential Energy Between

Charged Particles

=

r

qq 21

0potential

4

1E


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Bonding

a chemical bond forms when the potentialenergy of the bonded atoms is less than the

potential energy of the separate atoms have to consider following interactions:nucleus-to-nucleus repulsion

electron-to-electron repulsionnucleus-to-electron attraction


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Types of Bonds

Types of Atoms Type of BondBond

Characteristic

metals to

nonmetalsIonic

electrons

transferred

nonmetals to

nonmetalsCovalent

electrons

shared

metal to

metalMetallic

electrons

pooled


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Ionic Bonds

when metals bond to nonmetals, some electronsfrom the metal atoms are transferred to the

nonmetal atomsmetals have low ionization energy, relatively easy to

remove an electron from

nonmetals have high electron affinities, relativelygood to add electrons to


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Covalent Bonds

nonmetals have relatively high ionization energies, soit is difficult to remove electrons from them when nonmetals bond together, it is better in terms of

potential energy for the atoms to share valenceelectrons

potential energy lowest when the electrons are between thenuclei

shared electrons hold the atoms together by attractingnuclei of both atoms


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Determining the Number of Valence

Electrons in an Atom the column number on the Periodic Table will tell you

how many valence electrons a main group atom hasTransition Elements all have 2 valence electrons; Why?

1A 2A 3A 4A 5A 6A 7A 8A

Li Be B C N O F Ne

1 e-1 2 e-1 3 e-1 4 e-1 5 e-1 6 e-1 7 e-1 8 e-1


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Lewis Symbols of Atoms

aka electron dot symbols use symbol of element to represent nucleus and

inner electrons

use dots around the symbol to represent valenceelectronspair first two electrons for thes orbital

put one electron on each open side forp electrons

then pair rest of thep electrons

Li Be

B

C

N

O

F

Ne


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Lewis Symbols of Ions

Cations have Lewis symbols withoutvalence electrons

Lost in the cation formation

Anions have Lewis symbols with 8 valenceelectrons

Electrons gained in the formation of the anion

Li Li+1

F

1

F


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Octet Rule when atoms bond, they tend to gain, lose, or share electrons to

result in 8 valence electrons

ns2np6 noble gas configuration

many exceptions H, Li, Be, B attain an electron configuration like He

He = 2 valence electrons

Li loses its one valence electronH shares or gains one electron

though it commonly loses its one electron to become H+

Be loses 2 electrons to become Be2+

though it commonly shares its two electrons in covalent bonds, resulting in 4valence electrons

B loses 3 electrons to become B3+ though it commonly shares its three electrons in covalent bonds, resulting in 6

valence electrons

expanded octets for elements in Period 3 or below using empty valence dorbitals


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Lewis Theory

the basis of Lewis Theory is that there arecertain electron arrangements in the atom thatare more stable

octet rule

bonding occurs so atoms attain a more stableelectron configuration

more stable = lower potential energyno attempt to quantify the energy as the calculation

is extremely complex


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Energetics of Ionic Bond Formation

the ionization energy of the metal is endothermicNa(s) Na+(g) + 1 e H = +603 kJ/mol

the electron affinity of the nonmetal is exothermicCl2(g) + 1 e

Cl(g) H = 227 kJ/mol

generally, the ionization energy of the metal is largerthan the electron affinity of the nonmetal, therefore theformation of the ionic compound should beendothermic

but the heat of formation of most ionic compounds isexothermic and generally large; Why?Na(s) + Cl2(g) NaCl(s) Hf = -410 kJ/mol


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Ionic Bonds

electrostatic attraction is nondirectional!!no direct anion-cation pair

no ionic molecule

chemical formula is an empirical formula, simplygiving the ratio of ions based on charge balance

ions arranged in a pattern called a crystal lattice

every cation surrounded by anions; and every anionsurrounded by cations

maximizes attractions between + and - ions


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Born-Haber Cycle

method for determining the lattice energy of anionic substance by using other reactionsuse Hesss Law to add up heats of other processes

H

f(salt) = H

f(metal atoms, g) + H

f(nonmetal atoms, g)

+ Hf(cations, g) + Hf(anions, g) + Hf(crystal lattice)

Hf(crystal lattice) = Lattice Energy

metal atoms (g) cations (g), Hf = ionization energy

dont forget to add together all the ionization energies to get to the

desired cation

M2+ = 1st IE + 2nd IE

nonmetal atoms (g) anions (g), Hf = electron affinity


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Trends in Lattice Energy

Ion Size

the force of attraction between chargedparticles is inversely proportional to the

distance between them

larger ions mean the center of positive charge(nucleus of the cation) is farther away from

negative charge (electrons of the anion)

larger ion = weaker attraction = smaller lattice

energy


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Trends in Lattice Energy

Ion Charge the force of attraction between

oppositely charged particles is

directly proportional to the product

of the charges larger charge means the ions are

more strongly attracted

larger charge = stronger attraction =

larger lattice energy

of the two factors, ion chargegenerally more important

Lattice Energy =

-910 kJ/mol

Lattice Energy =

-3414 kJ/mol


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Ionic Bonding

Model vs. Reality ionic compounds have high melting points and boiling

points

MP generally > 300C

all ionic compounds are solids at room temperature

because the attractions between ions are strong,breaking down the crystal requires a lot of energy

the stronger the attraction (larger the lattice energy), the

higher the melting point


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Ionic Bonding

Model vs. Reality ionic compounds conduct electricity in the liquid state

or when dissolved in water, but not in the solid state

to conduct electricity, a material must have chargedparticles that are able to flow through the material

in the ionic solid, the charged particles are locked inposition and cannot move around to conduct

in the liquid state, or when dissolved in water, the ionshave the ability to move through the structure and

therefore conduct electricity


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Covalent Bonding:

Bonding and Lone Pair Electrons Covalent bonding results when atoms share pairs

of electrons to achieve an octet

Electrons that are shared by atoms are called

bonding pairs Electrons that are not shared by atoms but belong

to a particular atom are called lone pairs

aka nonbonding pairs

O S O

Lone PairsBonding Pairs


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Single Covalent Bonds

two atoms share a pair of electrons2 electrons

one atom may have more than one single bond

F

F

F

F

HH O

HH O

F F


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Double Covalent Bond

two atoms sharing two pairs of electrons4 electrons

O

O

O

O

O O


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Triple Covalent Bond

two atoms sharing 3 pairs of electrons6 electrons

N

N

N

N

N N


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Covalent Bonding

Model vs. Reality molecular compounds have low melting points and

boiling pointsMP generally < 300C

molecular compounds are found in all 3 states at roomtemperature

melting and boiling involve breaking the attractionsbetween the molecules, but not the bonds betweenthe atoms the covalent bonds are strong the attractions between the molecules are generally weak the polarity of the covalent bonds influences the strength of

the intermolecular attractions


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Ionic Bonding

Model vs. Reality

some molecular solids are brittle and hard, butmany are soft and waxy

the kind and strength of the intermolecularattractions varies based on many factors

the covalent bonds are not broken, however, thepolarity of the bonds has influence on these

attractive forces


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Ionic Bonding

Model vs. Reality molecular compounds do not conduct electricity in the

liquid state

molecular acids conduct electricity when dissolved inwater, but not in the solid state

in molecular solids, there are no charged particlesaround to allow the material to conduct

when dissolved in water, molecular acids are ionized,and have the ability to move through the structure and

therefore conduct electricity


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Bond Polarity covalent bonding between unlike atoms results in

unequal sharing of the electronsone atom pulls the electrons in the bond closer to its

side

one end of the bond has larger electron density than theother

the result is a polar covalent bondbond polarity

the end with the larger electron density gets a partialnegative charge

the end that is electron deficient gets a partial positivecharge


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Electronegativity

measure of the pull an atom has on bondingelectrons

increases across period (left to right) and

decreases down group (top to bottom)fluorine is the most electronegative element

francium is the least electronegative element

the larger the difference inelectronegativity, the more polar the bondnegative end toward more electronegative atom


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29

Electronegativity and Bond Polarity If difference in electronegativity between bonded atoms

is 0, the bond is pure covalentequal sharing

If difference in electronegativity between bonded atomsis 0.1 to 0.4, the bond is nonpolar covalent

If difference in electronegativity between bonded atoms0.5 to 1.9, the bond is polar covalent

If difference in electronegativity between bonded atomslarger than or equal to 2.0, the bond is ionic

100%

0 0.4 2.0 4.0

4% 51%Percent Ionic Character

Electronegativity Difference


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Bond Dipole Moments the dipole moment is a quantitative way of describing the

polarity of a bonda dipole is a material with positively and negatively charged ends

measured

dipole moment, , is a measure of bond polarity it is directly proportional to the size of the partial charges anddirectly proportional to the distance between them

= (q)(r)

not Coulombs Lawmeasured in Debyes, D

the percent ionic character is the percentage of a bondsmeasured dipole moment to what it would be if full ions


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Lewis Structures use common bonding patternsC = 4 bonds & 0 lone pairs, N = 3 bonds & 1 lone pair,

O= 2 bonds & 2 lone pairs, H and halogen = 1 bond, Be

= 2 bonds & 0 lone pairs, B = 3 bonds & 0 lone pairs

often Lewis structures with line bonds have the lone

pairs left off their presence is assumed from common bonding patterns

structures which result in bonding patternsdifferent from common have formal charges

B C N O F


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Exceptions to the Octet Rule

expanded octetselements with empty dorbitals can have more

than 8 electrons

odd number electron species e.g., NOwill have 1 unpaired electron

free-radical

very reactive incomplete octetsB, Al


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Bond Energies chemical reactions involve breaking bonds in reactant

molecules and making new bond to create the products

the Hreaction can be calculated by comparing the cost

of breaking old bonds to the profit from making newbonds

the amount of energy it takes to break one mole of abond in a compound is called the bond energy

in the gas state

homolytically each atom gets bonding electrons


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Using Bond Energies to Estimate Hrxn the actual bond energy depends on the surrounding

atoms and other factors

we often use average bond energies to estimate the Hrxnworks best when all reactants and products in gas state

bond breaking is endothermic, H(breaking) = +

bond making is exothermic, H(making) = Hrxn = (H(bonds broken)) + (H(bonds formed))


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Bond Lengths

the distance between the nuclei ofbonded atoms is called the bondlength

because the actual bond lengthdepends on the other atoms aroundthe bond we often use the average

bond lengthaveraged for similar bonds from

many compounds


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Trends in Bond Lengths

the more electrons two atoms share, the shorter thecovalent bond

CC (120 pm) < C=C (134 pm) < CC (154 pm)

CN (116 pm) < C=N (128 pm) < CN (147 pm)

decreases from left to right across periodCC (154 pm) > CN (147 pm) > CO (143 pm)

increases down the columnFF (144 pm) > ClCl (198 pm) > BrBr(228 pm)

in general, as bonds get longer, they also get weaker


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Metallic Bonds

low ionization energy of metals allows them tolose electrons easily the simplest theory of metallic bonding involves

the metals atoms releasing their valence electrons

to be shared by all to atoms/ions in the metalan organization of metal cation islands in a sea of

electrons

electrons delocalized throughout the metal structure

bonding results from attraction of cation for thedelocalized electrons


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Metallic Bonding

Model vs. Reality

metallic solids conduct electricity because the free electrons are mobile, it

allows the electrons to move through themetallic crystal and conduct electricity

as temperature increases, electricalconductivity decreases

heating causes the metal ions to vibratefaster, making it harder for electrons tomake their way through the crystal


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Metallic Bonding

Model vs. Reality

metallic solids conduct heat

the movement of the small, light electrons

through the solid can transfer kinetic energyquicker than larger particles

metallic solids reflect light

the mobile electrons on the surface absorbthe outside light and then emit it at the same

frequency


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Metallic Bonding

Model vs. Reality

metallic solids are malleable and ductile because the free electrons are mobile, the

direction of the attractive force between themetal cation and free electrons is adjustable

this allows the position of the metal cationislands to move around in the sea of

electrons without breaking the attractionsand the crystal structure


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Metallic Bonding

Model vs. Reality metals generally have high melting points and boiling

pointsall but Hg are solids at room temperature

the attractions of the metal cations for the free electronsis strong and hard to overcome

melting points generally increase to right across period the charge on the metal cation increases across the

period, causing stronger attractions

melting points generally decrease down column the cations get larger down the column, resulting in a

larger distance from the nucleus to the free electrons


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Structure Determines Properties!

properties of molecular substances depend onthe structure of the molecule

the structure includes many factors, including:

the skeletal arrangement of the atomsthe kind of bonding between the atomsionic, polar covalent, or covalent

the shape of the molecule

bonding theory should allow you to predict theshapes of molecules


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Using Lewis Theory to Predict

Molecular Shapes Lewis theory predicts there are regions of

electrons in an atom based on placing shared

pairs of valence electrons between bondingnuclei and unshared valence electrons located

on single nuclei

this idea can then be extended to predict theshapes of molecules by realizing these regions

are all negatively charged and should repel


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VSEPR Theory

electron groups around the central atom will bemost stable when they are as far apart aspossible we call this valence shell electron

pair repulsion theorysince electrons are negatively charged, they shouldbe most stable when they are separated as much aspossible

the resulting geometric arrangement will allowus to predict the shapes and bond angles in themolecule


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Electron Groups the Lewis structure predicts the arrangement of valence

electrons around the central atom(s) each lone pair of electrons constitutes one electron group

on a central atom

each bond constitutes one electron group on a centralatom regardless of whether it is single, double, or triple

O N O

there are 3 electron groups on N1 lone pair

1 single bond

1 double bond


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Molecular Geometries

there are 5 basic arrangements of electron groupsaround a central atombased on a maximum of 6 bonding electron groups

though there may be more than 6 on very large atoms, it is very rare

each of these 5 basic arrangements results in 5 differentbasic molecular shapes in order for the molecular shape and bond angles to be a

perfect geometric figure, all the electron groups must bebonds and all the bonds must be equivalent

for molecules that exhibit resonance, it doesnt matterwhich resonance form you use the moleculargeometry will be the same


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Linear Geometry when there are 2 electron groups around the central

atom, they will occupy positions opposite each otheraround the central atom

this results in the molecule taking a linear geometry the bond angle is 180

ClBeCl

OCO


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Trigonal Geometry when there are 3 electron groups around the central

atom, they will occupy positions in the shape of atriangle around the central atom

this results in the molecule taking a trigonal planargeometry

the bond angle is 120

F

FBF


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Not Quite Perfect Geometry

Because the bonds are

not identical, the

observed angles are

slightly different from

ideal.


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Tetrahedral Geometry when there are 4 electron groups around the central

atom, they will occupy positions in the shape of atetrahedron around the central atom

this results in the molecule taking a tetrahedralgeometry

the bond angle is 109.5

F

FCF

F


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Trigonal Bipyramidal Geometry when there are 5 electron groups around the central atom, they

will occupy positions in the shape of a two tetrahedra that arebase-to-base with the central atom in the center of the shared

bases

this results in the molecule taking a trigonal bipyramidal

geometry the positions above and below the central atom are called the

axial positions

the positions in the same base plane as the central atom are

called the equatorial positions the bond angle between equatorial positions is 120

the bond angle between axial and equatorial positions is 90


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Octahedral Geometry

when there are 6 electron groups around the centralatom, they will occupy positions in the shape of twosquare-base pyramids that are base-to-base with thecentral atom in the center of the shared bases

this results in the molecule taking an octahedralgeometry it is called octahedral because the geometric figure has 8

sides

all positions are equivalent the bond angle is 90


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The Effect of Lone Pairs

lone pair groups occupy more space on the centralatombecause their electron density is exclusively on the

central atom rather than shared like bonding electrongroups

relative sizes of repulsive force interactions is:Lone Pair Lone Pair > Lone Pair Bonding Pair > Bonding Pair Bonding Pair

this effects the bond angles, making them smallerthan expected


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Derivative Shapes

the molecules shape will be one of basicmolecular geometries if all the electron groups

are bonds and all the bonds are equivalent molecules with lone pairs or different kinds of

surrounding atoms will have distorted bond

angles and different bond lengths, but the shapewill be a derivative of one of the basic shapes


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Derivative of Trigonal Geometry when there are 3 electron groups around the central

atom, and 1 of them is a lone pair, the resulting shape

of the molecule is called a trigonal planar - bent

shape

the bond angle is < 120

OSO

OSO

OSO

Derivatives of Tetrahedral


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Derivatives of Tetrahedral

Geometry

when there are 4 electron groups around the centralatom, and 1 is a lone pair, the result is called apyramidal shapebecause it is a triangular-base pyramid with the central

atom at the apex

when there are 4 electron groups around the centralatom, and 2 are lone pairs, the result is called atetrahedral-bent shape it is planar

it looks similar to the trigonal planar-bent shape, except theangles are smaller

for both shapes, the bond angle is < 109.5

Derivatives of the


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Derivatives of the

Trigonal Bipyramidal Geometry when there are 5 electron groups around the central atom, and

some are lone pairs, they will occupy the equatorial positionsbecause there is more room

when there are 5 electron groups around the central atom, and1 is a lone pair, the result is called see-saw shape

aka distorted tetrahedron

when there are 5 electron groups around the central atom, and2 are lone pairs, the result is called T-shaped

when there are 5 electron groups around the central atom, and

3 are lone pairs, the result is called a linear shape the bond angles between equatorial positions is < 120

the bond angles between axial and equatorial positions is 1000C

dimensionality of the network affects other physicalproperties

The Diamond Structure:


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a 3-Dimensional Network

the carbon atoms in a diamond each have 4covalent bonds to surrounding atoms

sp

3

tetrahedral geometry

this effectively makes each crystal one giant

molecule held together by covalent bondsyou can follow a path of covalent bonds from any

atom to every other atom

The Graphite Structure:

2 Di i l N k


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a 2-Dimensional Network

in graphite, the carbon atoms in a sheet are covalentlybonded together forming 6-member flat rings fused together

similar to benzenebond length = 142 pm

sp2each C has 3 sigma and 1 pi bond

trigonal-planar geometryeach sheet a giant molecule

the sheets are then stacked and held together bydispersion forcessheets are 341 pm apart

Band Theor


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Band Theory

the structures of metals and covalent networksolids result in every atoms orbitals being

shared by the entire structure for large numbers of atoms, this results in a

large number of molecular orbitals that have

approximately the same energy, we call this an

energy band

Band Theory


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Band Theory when 2 atomic orbitals combine they produce

both a bonding and an antibonding molecularorbital

when many atomic orbitals combine they

produce a band of bonding molecular orbitalsand a band of antibonding molecular orbitals

the band of bonding molecular orbitals is calledthe valence band

the band of antibonding molecular orbitals iscalled the conduction band

Band Gap


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Band Gap

at absolute zero, all the electrons will occupy thevalence band

as the temperature rises, some of the electrons

may acquire enough energy to jump to theconduction band

the difference in energy between the valence

band and conduction band is called the band gapthe larger the band gap, the fewer electrons there are

with enough energy to make the jump

Band Gap and Conductivity the more electrons at any one time that a substance has in the


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yconduction band, the better conductor of electricity it is

if the band gap is ~0, then the electrons will be almost as likelyto be in the conduction band as the valence band and thematerial will be a conductor metals

the conductivity of a metal decreases with temperature

if the band gap is small, then a significant number of theelectrons will be in the conduction band at normal temperaturesand the material will be a semiconductor graphite

the conductivity of a semiconductor increases with temperature

if the band gap is large, then effectively no electrons will be inthe conduction band at normal temperatures and the materialwill be an insulator

Doping Semiconductors


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doping is adding impurities to the semiconductorscrystal to increase its conductivity

goal is to increase the number of electrons in theconduction band

n-type semiconductors do not have enough electronsthemselves to add to the conduction band, so they aredoped by adding electron rich impurities

p-type semiconductors are doped with an electrondeficient impurity, resulting in electron holes in thevalence band. Electrons can jump between these holesin the valence band, allowing conduction of electricity

Diodes


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Diodes

when a p-type semiconductor adjoins an n-typesemiconductor, the result is an p-n junction

electricity can flow across the p-n junction inonly one direction this is called a diode

this also allows the accumulation of electrical

energy called an amplifier

Solubility


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when one substance (solute) dissolves in another

(solvent) it is said to be solublesalt is soluble in waterbromine is soluble in methylene chloride

when one substance does not dissolve in another it is

said to be insolubleoil is insoluble in water

the solubility of one substance in another

depends on two factors natures tendencytowards mixing, and the types of

intermolecular attractive forces

Solubility


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y there is usually a limit to the solubility of one

substance in anothergases are alwayssoluble in each othertwo liquids that are mutually soluble are said to be

misciblealcohol and water are miscibleoil and water are immiscible

the maximum amount of solute that can be dissolvedin a given amount of solvent is called the solubility

the solubility of one substance in another varies withtemperature and pressure

Mixing and the Solution Process

Entropy


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Entropy

formation of a solution does not necessarilylower the potential energy of the system the difference in attractive forces between atoms of

two separate ideal gases vs. two mixed ideal gasesis negligible

yet the gases mix spontaneously

the gases mix because the energy of thesystem is lowered through the release ofentropy

entropy is the measure of energy dispersalthroughout the system

energy has a spontaneous drive to spread outover as large a volume as it is allowed

Relative Interactions and Solution Formation


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when the solute-to-solvent attractions are weaker thanthe sum of the solute-to-solute and solvent-to-solvent

attractions, the solution will only form if the energydifference is small enough to be overcome by theentropy

Solute-to-Solvent >Solute-to-Solute +

Solvent-to-SolventSolution Forms

Solute-to-Solvent =Solute-to-Solute +

Solvent-to-SolventSolution Forms

Solute-to-Solvent < Solute-to-Solute +Solvent-to-Solvent

Solution May orMay Not Form

Will It Dissolve?


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Chemists Rule of Thumb

Like Dissolves Like

a chemical will dissolve in a solvent if it has a similarstructure to the solvent

when the solvent and solute structures are similar,the solvent molecules will attract the solute particles

at least as well as the solute particles to each other

Heats of Hydration


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Heats of Hydration

for aqueous ionic solutions, the energy added toovercome the attractions between water molecules and

the energy released in forming attractions between the

water molecules and ions is combined into a termcalled the heat of hydration

attractive forces in water = H-bonds

attractive forces between ion and water = ion-dipole

Hhydration = heat released when 1 mole of gaseous ionsdissolves in water

Solution Equilibrium


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the dissolution of a solute in a solvent is an equilibriumprocess

initially, when there is no dissolved solute, the onlyprocess possible is dissolution

shortly, solute particles can start to recombine toreform solute molecules but the rate of dissolution >>

rate of deposition and the solute continues to dissolve

eventually, the rate of dissolution = the rate ofdeposition the solution is saturated with solute and no

more solute will dissolve

Solubility Limit


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Solubility Limit

a solution that has the maximum amount of solutedissolved in it is said to be saturated

depends on the amount of solvent

depends on the temperatureand pressure of gases

a solution that has less solute than saturation is said tobe unsaturated

a solution that has more solute than saturation is said tobe supersaturated

Temperature Dependence of Solubility


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of Solids in Water

solubility is generally given in grams of solute that willdissolve in 100 g of water

formost solids, the solubility of the solid increases asthe temperature increases

when Hsolution is endothermic

solubility curves can be used to predict whether a

solution with a particular amount of solute dissolved inwater is saturated (on the line), unsaturated (below the

line), or supersaturated (above the line)

Temperature Dependence of Solubility


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of Gases in Water solubility is generally given in moles of solute

that will dissolve in 1 Liter of solution

generally lower solubility than ionic or polar

covalent solids because most are nonpolarmolecules

forall gases, the solubility of the gas decreases

as the temperature increasesthe Hsolution is exothermic because you do not needto overcome solute-solute attractions

Pressure Dependence of Solubility of


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151

Gases in Water

the larger the partial pressure of a gas in contactwith a liquid, the more soluble the gas is in theliquid

Henrys Law


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Henry s Law

the solubility of a gas (Sgas) is

directly proportional to its

partial pressure, (Pgas)Sgas = kHPgas

kH is called Henrys Law

Constant

Concentrations


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Concentrations

solutions have variable composition to describe a solution, need to describe components

andrelative amounts

the terms dilute and concentrated can be used asqualitative descriptions of the amount of solute insolution

concentration = amount of solute in a given amount ofsolutionoccasionally amount of solvent

Solution Concentration

Molarity


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Molarity

moles of solute per 1 liter of solution used because it describes how many

molecules of solute in each liter of solution

if a sugar solution concentration is 2.0 M,1 liter of solution contains 2.0 moles of

sugar, 2 liters = 4.0 moles sugar, 0.5 liters

= 1.0 mole sugarmolarity =

moles of solute

liters of solution


M l li


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Molality, m moles of solute per 1 kilogram of solventdefined in terms of amount of solvent, not solution

like the others

does not vary with temperaturebecause based on masses, not volumes

solventofkgsoluteofmolesmmolality, =

Percent


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parts of solute in every 100 parts solution

mass percent = mass of solute in 100 partssolution by massif a solution is 0.9% by mass, then there are 0.9

grams of solute in every 100 grams of solutionor 0.9 kg solute in every 100 kg solution

SolutionofMassSolventofMassSoluteofMass

%100

gSolution,ofMass

gSolute,ofMassPercentMass

=+

=

Percent Concentration( l t )P t


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SolutionofMassSolventofMassSoluteofMass

%100gSolution,ofMass

gSolute,ofMassPercentMass

=+

=

SolutionofVolumeSolventofVolumeSoluteofMass

%100mLSolution,ofVolume

gSolute,ofMasseMass/VolumPercent

+

=

SolutionofVolumeSolventofVolumeSoluteofVolume

%100mLSolution,ofVolume

mLSolute,ofVolumePercentVolume

+

=

%100

(solution)Whole

(solute)PartPercent =

Using Concentrations as


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Conversion Factors

concentrations show the relationship betweenthe amount of solute and the amount of solvent12%(m/m) sugar(aq) means 12 g sugar 100 g solution

or 12 kg sugar 100 kg solution; or 12 lbs. 100 lbs. solution

5.5%(m/v) Ag in Hg means 5.5 g Ag 100 mL solution22%(v/v) alcohol(aq) means 22 mL EtOH 100 mL solution

The concentration can then be used to convert theamount of solute into the amount of solution, or viceversa

Preparing a Solution
http://wps.prenhall.com/wps/media/objects/477/488990/st1301.htmlhttp://wps.prenhall.com/wps/media/objects/477/488990/st1301.html


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need to know amount of solution andconcentration of solution

calculate the mass of solute needed

start with amount of solutionuse concentration as a conversion factor5% by mass 5 g solute 100 g solution

Dissolve the grams of solute in enough solvent to

total the total amount of solution.



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PPM

grams of solute per 1,000,000 g of solution

mg of solute per 1 kg of solution

1 liter of water = 1 kg of waterfor water solutions we often approximate the kg of

the solution as the kg or L of water

grams solutegrams solution x 106

mg solute

kg solution

mg solute

L solution

Solution ConcentrationsMole Fraction,XA


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, A

the mole fraction is the fraction of the moles of onecomponent in the total moles of all the componentsof the solution

total of all the mole fractions in a solution = 1

unitless the mole percentage is the percentage of the moles

of one component in the total moles of all thecomponents of the solution

= mole fraction x 100%

mole fraction ofA =XA =moles of components A

total moles in the solution

Converting Concentration Units assume a convenient amount of solution

given %(m/m) assume 100 g solution


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given %(m/m), assume 100 g solution

given %(m/v), assume 100 mL solution

given ppm, assume 1,000,000 g solution

given M, assume 1 liter of solution

given m, assume 1 kg ofsolvent

givenX, assume you have a total of 1 mole of solutes in the solution

determine amount of solution in non-given unit(s) if assume amount of solution in grams, use density to convert to mL andthen to L

if assume amount of solution in L or mL, use density to convert to grams

determine the amount of solute in this amount of solution, in

grams and moles determine the amount of solvent in this amount of solution, in

grams and moles

use definitions to calculate other units

Thirsty Solutions


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Thirsty Solutions

a concentrated solution will draw solventmolecules toward it due to the natural drive for

materials in nature to mix

similarly, a concentrated solution will draw puresolvent vapor into it due to this tendency to mix

the result is reduction in vapor pressure

Raoults Law


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Raoult s Law

the vapor pressure of a volatile solvent above asolution is equal to its mole fraction of its

normal vapor pressure,P

Psolvent in solution = solventPsince the mole fraction is always less than 1, the

vapor pressure of the solvent in solution will always

be less than the vapor pressure of the pure solvent

Ionic Solutes and Vapor Pressuredi R l L h ff f l


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according to Raoults Law, the effect of solute on

the vapor pressure simply depends on the numberof solute particles

when ionic compounds dissolve in water, theydissociate so the number of solute particles is a

multiple of the number of moles of formula units

the effect of ionic compounds on the vaporpressure of water is magnified by the dissociation

since NaCl dissociates into 2 ions, Na+ and Cl, onemole of NaCl lowers the vapor pressure of water twice

as much as 1 mole of C12H22O11 molecules would

Raoults Law for Volatile Solute


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when both the solvent and the solute can evaporate,both molecules will be found in the vapor phase

the total vapor pressure above the solution will be thesum of the vapor pressures of the solute and solvent

for an ideal solution

Ptotal = Psolute + Psolvent

the solvent decreases the solute vapor pressure in the

same way the solute decreased the solvents

Psolute = solutePsolute and Psolvent = solventPsolvent

Ideal vs. Nonideal Solution


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in ideal solutions, the made solute-solventinteractions are equal to the sum of the broken

solute-solute and solvent-solvent interactions

ideal solutions follow Raoults Law

effectively, the solute is diluting the solvent

if the solute-solvent interactions are stronger or

weaker than the broken interactions the solutionis nonideal

Vapor Pressure of a

N id l S l ti


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Nonideal Solution when the solute-solvent interactions are stronger than

the solute-solute + solvent-solvent, the total vapor

pressure of the solution will be less than predicted by

Raoults Lawbecause the vapor pressures of the solute and solvent are

lower than ideal

when the solute-solvent interactions are weaker than

the solute-solute + solvent-solvent, the total vaporpressure of the solution will be larger than predicted by

Raoults Law

Freezing Point Depression the freezing point of a solution is lower than the freezing


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point of the pure solvent

for a nonvolatile solute

therefore the melting point of the solid solution is lower

the difference between the freezing point of the solutionand freezing point of the pure solvent is directly

proportional to the molal concentration of solute particles

(FPsolvent FPsolution) = Tf = mKf the proportionality constant is called the Freezing Point

Depression Constant,Kf the value ofKf depends on the solvent

the units ofKf are C/m

Boiling Point Elevation the boiling point of a solution is higher than the boiling


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g p g g

point of the pure solvent for a nonvolatile solute

the difference between the boiling point of the solutionand boiling point of the pure solvent is directly

proportional to the molal concentration of soluteparticles

(BPsolution BPsolvent) = Tb = mKb the proportionality constant is called the Boiling Point

Elevation Constant, Kb the value of Kb depends on the solvent

the units of Kb are C/m

Osmosis osmosis is the flow of solvent through a semi-


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osmosis is the flow of solvent through a semi

permeable membrane from solution of lowconcentration to solution of high concentration

the amount of pressure needed to keep osmotic

flow from taking place is called the osmoticpressure

the osmotic pressure, , is directly proportional

to the molarity of the solute particlesR = 0.08206 (atmL)/(molK)

= MRT

Colligative Properties

lli i i i h l


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colligative properties are properties whose value

depends only on the number of solute particles, and noton what they are

Vapor Pressure Depression, Freezing Point Depression,

Boiling Point Elevation, Osmotic Pressure

the vant Hoff factor, i, is the ratio of moles of soluteparticles to moles of formula units dissolved

measured vant Hoff factors are often lower than you

might expect due to ion pairing in solution


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Colloids


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a colloidal suspension is a heterogeneousmixture in which one substance is dispersed

through another

most colloids are made of finely divided particles

suspended in a medium

the difference between colloids and regularsuspensions is generally particle size colloidal

particles are from 1 to 100 nm in size

Properties of Colloids


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p

the particles in a colloid exhibit Brownianmotion

colloids exhibit the Tyndall Effectscattering of light as it passes through a suspensioncolloids scatter short wavelength (blue) light more

effectively than long wavelength (red) light

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