[Notes]CHEM15.0 - Fundamentals of Chemistry

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CHEM 15.0 Notes by F5XS Fundamentals of Chemistry

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Chemistry is the study of matter (composition, structure and properties), thechanges it undergoes, and the energy transformations that accompany those

changes.

Matter is the stuff that makes up all material things.

Energy is the capacity to do work or to produce charge.

Technology is the sum total of the processes by which humans modify thematerials of nature to better satisfy their needs and wants. Science is thesystematically allocated and organized body of knowledge based onexperimentation, observation, and careful reasoning. Both of which should bestable, explanatory, and tentative.

Interdependence of science and technology

new technology often requires new understanding

new investigations in science require new technology

The scientific method is a process that lies at the center of scientific inquiry.1] definition of the problem2] data collection/observation3] formulation of hypothesis and testing4] evolution into theory after repeated testing

Hypothesis tentative explanation for a set of observations

validity tested by further experiments

Natural Law

empirical generalization describing the behavior of nature

may be in the form of a qualitative statement or a mathematical formula

A theory is an explanation of observed behavior in terms of a simple modelthat has familiar properties.

A model is a mental image of a phenomenon in terms of something we arefamiliar with; “makes visible the invisible” .

The quality of the investigation and of our resulting understanding of theuniverse depends on…

the cleverness of the questions asked

the skill with which the experiments are carried out

the skill of the investigator to convert the results of the experiment into an ever more sophisticated understanding of the universe

Chemistry/Science is affected by:

budget and profit motives wars and politics

fads and religious beliefs




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Matter

it is the material of the universe

anything that occupies space, has mass and possesses inertia

Mass

amount of matter

constant property of a material regardless of location

equivalent to weight of an object at the same location

Weight

measure of force with which an object of a given mass is attracted by gravity

varies with elevation or distance from gravitational source

Volume is the space occupied by matter.

(Basic) States of Matter

gas – no fixed volume or shape

liquid – distinct volume independent of its container; no specific shape

solid – definite shape and volume

Any material under a study may be a homogenous system or aheterogeneous system.

A phase is, in a sample of matter, any portion that is homogenous andseparated from other part of the sample by a definite surface or boundary.

A property is a characteristic that can be noted to describe or identify matter. An extensive property depends on the amount of substance contained while anintensive property does not depend on the amount of substance contained.

A physical change is a type of change wherein the sample undergoes achange in physical appearance but not in composition while a chemical change is another type of change wherein the sample is transformed into a chemicallydifferent substance. Nuclear change is another type of change wherein the

change originates in the nucleus of an atom; the number and identity of theatoms or elements change.

A pure substance has a fixed composition while a mixture is a combinationof two or more substances in which each substance retains its own chemicalidentity.

An element cannot be broken down into simpler substances by chemicalmeans while a compound is composed of two or more elements unitedchemically in definite proportions.

Ancient views on matter: Chinese and Greek Philosophers

based on speculation

Chinese book, “Shuching,” claimed that matter is made up of earth, fire, water,metal, and wood




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Empedocles of Greece claimed that matter is made up of fire, earth, water,and air

Leucippus and Democritus described matter as “atomos

” (particulate) whileAristotle described matter as “hule” (continuous)

John Dalton, 1803, observed through careful experimental observations andmeasurements that atoms are indivisible, much like a billiard ball, and has mass.This became the first scientific theory of the atom and this was the basis for thebilliard ball model of the atom. He was the first to assign specific masses for eachatom.Dalton’s postulates

matter is composed of tiny indivisible particles called atoms

all atoms of a given element are identical, but differ from atoms of other

elements compound is composed of the atoms of its elements in a definite fixed

numerical ratio

chemical reaction involves the rearranging in atoms in different combinations,the atoms remain intact and do not change

1850’s experiments started to show that atoms possess an inner structure

details on the structure of the atom were made possible due to the advent of …

powerful sources of electrical voltage

studies with gas discharge tubes called “Crooke’s Tube”

discovery of X-rays and radioactivityCrooke’s Tube

glass tube containing gas under low pressure

passing an electric current makes a beam appear to move from the negativeend to the positive end

(Joseph J. Thomson’s observation) rays from the cathode travel in a straightline going to the anode

(Joseph J. Thomson’s observation) adding an electric plate on either side of the tube deflects the beams

Thomson Model (plum pudding model)

atoms can be subdivided into electrically charged particles with which hecalled cathode rays

cathode rays travel in a straight line s evidenced by a shadow that forms whenan object blocks its path

Rutherford’s α-scattering experimentObservation Interpretation

99% of the α particles went straightthrough the gold foil

the atom is mostly empty space

some of the α particles had small

angle deflections

attractive encounters with the

negative electron big angle deflection by some α

particles close encounters with a highly

positive region

a very small percent of the α particleswere deflected back

a direct hit at a very small equallymassive portion




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Characteristics of Rutherford’s nuclear atom

the atom consists of very small, very dense nucleus which is positively

charged, containing most of its mass the atom is mostly empty space and the volume is occupied by the practically

a massless electron

the positively charged concentrated in the nucleus is neutralized by thenegatively charged electrons moving around the nucleus

the estimated radius of the nucleus is 1/50000 times the radius of the atom

Eugene Goldstein’s proton, 1886

used a cathode with holes in a discharged or cathode tube, observed rayspassing through the holes in the cathode opposite the direction of the cathoderays

named it as canal rays consisting of positively charged particles with differed inmass and charge depending on the gas inside the tube

1840 times heavier than the electron

James Chadwick, 1932, the proton

bombarded a thin sheet of Beryllium with α particles

emission of very high energy radiation similar to γ rays

high energy radiation consisted of electrically neutral particles with massslightly greater than that of the proton

Main features of the Atom atoms consist of a cloud of negatively charged electrons

the electron cloud occupies most of the volume of the atom

the nucleus consists of protons and neutrons (collectively known as nucleons)

atoms are electrically neutral

the number of protons (and electrons) of one element is different from thenumber of protons (and electrons) in atoms of any other element

the number of protons in the atom of an element (also the number of electrons) is the atomic number (Z)

mass of an atom is accounted mostly by the nucleons

+

=

, which is the mass number

= +

atoms of the same element which varies in the number of neutrons but havethe same number of protons are called isotopes

Name Symbol Charge Relative Mass Actual Mass (g)

Electron − +1 1/1840 9.11 × 10−28 Proton + −1 1 1.67 × 10−24

Neutron 0 1 1.67 × 10−24

Notation: where is the mass number, is the atomic number, and is the chemical symbol.

Max Planck, 1900

studied the profile of electromagnetic radiation emitted by solids heated tovarious temperatures

intensity of light emitted by the hot object depends on the energyabsorbed/emitted (as gauged by temperature)




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“atoms and molecules could emit or absorb energy only in discrete quantitiesor bundles”, later called quantum

a quantum is the smallest quantity of energy that can be emitted or absorbedin the form of electromagnetic radiation

energy of a single quantum is equal to a constant multiplied by the frequencyof the electromagnetic radiation

= wherein is the Planck’s constant ( ≅ 6.63 × 10−34 ) and is the

frequency in

energy is always emitted or absorbed in whole number multiples of

Albert Einstein, 1905

used the quantum theory to solve the photoelectric effect

energy is quantized, transformed only in discrete quantities called quanta

electromagnetic radiation, which was thought to exhibit only wave properties,seem to show certain characteristics of particulate matter, which lead to thewave-particle duality of light

experiments important to the elucidation of atomic structure were carried outby physicists

Photoelectric Effect

electrons are emitted from the surface of a metal when light strikes it

could not be explained by the wave theory on light

electrons were ejected only when the metal surface was exposed to light of a

certain minimum frequency called threshold frequency

Electromagnetic radiation is a form of energy transmission through avacuum or a medium in which electric and magnetic components are propagatedas waves.

spectrum – component colors of light or electromagnetic radiation

emission spectrum – either continuous or line spectra of radiation emitted bya substance when heated or passed through a prism

continuous spectrum – emission spectrum of white light or sunlight

line spectrum – emission spectrum of atoms in the gas phase narrowcolored lines

Niels Bohr, 1913

used the emission spectrum of hydrogen

theory explaining the emission spectrum of the hydrogen atom and suggestedan explanation as to why atoms don’t collapse

electrons in the hydrogen atom moves around the nucleus only in certainallowable orbits

Bohr’s Model

only allowed energy levels (orbits) are possible for the electron

energy levels are numbered starting with 1 as the first orbit lowest energy state is the ground state which brings the electron closest to the

nucleus

Dalton → Thomson → Rutherford → Bohr → Quantum Mechanical Model




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Evolution of the Periodic Table 1] Johann Dobereiner – grouping of three elements, triads, with simple physical

and chemical properties2] John Newlands

law of octaves – eighth element starting from a given one is a kind of repetition of the first

arranged the elements in the order if increasing atomic weights3] Dmitri Ivanovich Mendeleev

produced a table on which the modern classification of elements is based

called it a periodic table, where elements with similar properties arearranged periodically

arranged in the order in increasing atomic masses4] Julius Lothar Meyer – only a few months after Mendeleev, he published a

similar classification of elements5] Henry Mosely showed that elements can be identified by their atomic number 6] Glenn Seaborg is responsible for bringing down the lanthanide and actinide

series in the present Periodic table

Periodic Law states that properties of the elements vary periodically with their atomic weights.

The modern periodic table

its basic structure and shape is one of the strongest empirical supports for thequantum theory that is used to predict electronic configuration

elements are arranged in the order of increasing atomic number

the darker boxes indicate metals while the lighter blocks indicate non-metals;the blocks in between non-metals and metals are the metalloids

horizontal rows pertain to periods while columns pertain to groups

1

2 13 14 15 16 17

18

s block d block

Transition Metals

p block

f block

Inner Transition Metals

Lathanide Series

Actinide Series

3 4 5 6 7 8 9 10 11 12




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The atomic mass is the weighted average of all (natural) isotopic masses of the element.

The effective nuclear charge (denoted as

) dictates the trends in the

periodic table. A higher effective nuclear charge will yield a stronger attraction of nucleus to the electrons. = − where…

is the nuclear charge which is related to attractive force of positively chargednucleus to the negative electrons

is the shielding constant, which is related to the number of inner shellsshielding the outer shell

usually more dominant than

Atomic properties and trends

periodicity of valence

most striking and significant periodic variation among elements in theperiodic table

representative elements exhibit this most consistently

valence shell electrons control the chemical properties of an element

periodic variation in the number of valence electrons leads to periodicvariation of chemical properties of elements

a “stable element” has energy levels completely filled with valence electronsand are relatively stable and generally unreactive (group 8, noble gases)

atomic size

the atomic radius is half the distance between two nuclei of a diatomic

molecule greatest at the lower left part of the table

ionization energy

energy needed to pull out the outermost electron

related to the tendency of the atom to form cations

greatest at the upper right part of the table

electron affinity

ability to accept one or more electrons

measure of the tightness of binding an additional electron

related to tendency to form cations

greatest at the lower left part of the table, with many exceptions includingthe noble gases

Valence Shell Electron Pair Repulsion (VSEPR)

used in predicting shapes of species that have main group elements as centralatom

C6

12.01

Atomic number

Chemical symbol

Atomic mass

Grp. # Category1 alkali metals

2 alkaline earth metals13 boron family14 carbon family15 nitrogen family16 oxygen family17 halogens18 noble gases




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electron pairs will be as far apart from each other in three-dimensional spaceas possible

The polarity of a molecule depends on the relative electronegativities of atoms that comprise it and molecule’s geometry.

Electronegativity is the capacity to attract electrons by a bonded atom.

Law of Conservation of Mass

demonstrated by Antoine Lavoisier (1743 – 1794), referred to as the Father of Modern Chemistry

established chemistry as a quantitative science

demonstrated by experiments with careful measurements that combustion

involves the reaction of a substance with oxygen when combustion is carried out in a closed container there is no net change

in mass

Law of Definite Proportions

Joseph Proust, 1799, pointed out that “a compound is a substance to whichnature assigns a fixed ratio”

showed that copper carbonate, whether prepared in the lab or obtained fromnatural sources, contained the same three elements: copper, carbon, andoxygen, and always in the same proportions

a pure chemical substance contains the same elements in the same definiteproportion by mass of its elements

the reaction where there are unreacted or excess illustrate the concept of limiting reactant

Law of Multiple Proportions

John Dalton predicted a regularity in the weight relations in the case of thesame two elements forming two or more different compounds

in different compounds of the same elements, the different masses of oneelement that combine with a fixed mass of the other element are in the ratio of small whole numbers

Chemical Arithmetic

in studying matter, we need to see and be able to count, weigh, and measureexact volumes of substances

we measure samples of elements that would contain their atoms in the specificratios that are needed

difficult to weigh a single atom because it is very minute

smallest speck of dust that is visible to the eye has 1 × 1016 particles

Atomic Mass

assign a value to the mass of one atom of a given element which is called thereference/standard

by international agreement, the reference element chosen was carbon-12

1 = mass exactly equal to1

12the mass of 1 C-12 atom

the atomic mass unit () of an element is the average atomic mass of allnaturally occurring mixture of a particular element




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if we take the relative mass of one element in any mass unit, this mass willcontain the same number of atoms as would be found in the relative mass of

some other element in the same units

The molecular mass is the sum of the atomic masses of the atoms in a givenchemical formula or covalent compounds.

The formula mass is the sum of the atomic masses of the atoms in a givenchemical formula of either a molecule or a formula unit of an ionic compound.

The chemical formula of a substance represents the kind and number of atoms of the respective elements in a molecular or formula unit of a compound.

Mole Concept

atoms react in simple whole number ratios atoms and molecules are too small to be seen much more to be counted

atoms and molecules are counted by relating number to mass

moles are counting units use by chemists

a mole contains the number of carbon-12 atoms contained in 12 of carbon-

12, which is equal to 6.02 × 1023 atoms/particles (6.02 × 1023 is theAvogadro’s number )

The number of moles of any substance can be measure using this formula:

=

mass ()

molar mass ()

Percentage composition states that, by the law of definitecompositions/proportions, a compound always has the same elements in thesame ratio by mass. In general, percent composition is taken to mean by massunless otherwise specified.

Empirical Formula

simplest formula

chemical formula that shows the…

kinds of atoms/elements

relative number (simplest ratio) of atoms of each element

Molecular Formula

simplest formula

chemical formula that shows the…

kinds of atoms/elements

actual number of atoms of each element

Most stable substances do not exist in the atomic form. Some elements existin the diatomic state. Atoms of different elements combine to form compounds.

When atoms combine, they are held together in fixed proportions by forces of attraction called chemical bonds.

Chemical changes consist of breaking of old bonds and the formation of newones. Atoms interact by changing the number of their valence electrons so as toacquire the electronic structure of a noble gas.




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Octet Rule – an atom gains, loses, or shares electrons in chemical bonding insuch a way as to attain a valence octet.

Electron Dot Symbols, a.k.a. Lewis Symbols, is a system devised to keeptrack of valence electrons in a chemical reaction.

There are three types of chemical bonds, namely metallic bonds, ionicbonds, and covalent bonds.

Metallic Bond

demonstrated by the sea-of-electrons model, an oversimplified theory of bonding in metals which can explain some of the observed properties of metals

the forces of attraction between the positive ions and the delocalized electrons in the crystal, the cations occupy fixed positions but the electrons move freely

throughout the crystal

Ionic Bond

the structural units or particles in the crystal are cations and anions

formula units of ionic compounds do not exist as separate entities

Covalent Bond

the bond that holds atoms together in molecules

the bond formed by sharing a pair of electrons

formed from the combination of nonmetallic elements

arises from the attraction of each electron in a shared pair to both of the nucleiinvolved in the bond

the two electrons spend most of their time somewhere between the two nuclei

Valence Bond Theory

a quantum mechanical model to describe the electronic nature of covalentbonds

provides an easily visualized picture of how electron pairs are shared in acovalent bond

covalent bonds are formed by the overlap of atomic orbitals each of whichcontains one electron of the opposite spin

each of the bonded atoms maintains its own atomic orbitals, but the electornpair in the overlapping orbitals is shared by most atoms

Multiple Covalent Bonds

atoms may attain complete octets by sharing more than one pair of electronsbetween them

the more bonds bonding the two atoms together, the tighter the atoms are heldtogether

The bond length is the distance between the centers of two atoms joined by acovalent bond. The bond length decreases as the number of shared pairsincreases.




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A coordinate covalent bond is a covalent bond in which one atomcontributes both electrons shared in the bond. The atom that contributed two

electrons is called the ligand.

Covalent compounds are compounds that contain only covalent bonds.There are two types of covalent compounds:

molecular covalent compounds contain discrete molecular units

network covalent compounds have no molecular units and have anextensive three-dimensional structure

There are two types of attractive forces in covalent compounds:

covalent bonds which are forces that hold the atoms together in the molecule

intermolecular forces of attraction which are forces that operate between

molecules

The bond polarity is a useful concept to describe unequal sharing of electrons in a bond.

Nonpolar covalent bonds have equal sharing of the electron pair in a bond.Equal sharing occurs in molecules of diatomic elements or in between identicalatoms with identical neighbors.

Polar ionic bond occurs when there is unequal sharing of electron pair in abond. Unequal sharing occurs when either two atoms are dissimilar or two atomsare identical but not identical in surroundings.

Electronegativity is the numerical measure of the ability of an atom in amolecule to attract the electrons shared in a bond; the greater an atom’selectronegativity, the greater its ability to attract electrons to itself. This is relatedto an atom’s electron affinity and ionization energy. This is used to estimatewhether a given bond will be nonpolar covalent, polar covalent, or ionic.

Electronegativity is the absolutevalue of the difference inelectronegativity values of the bondedatoms. This can be used to gauge thepolarity of the bonding between two atoms.

A Lewis structure describes how the electrons are distributed in a moleculeor ion.

The formal charge reveals the distribution of electrons in the molecule. It alsohelps in drawing the most plausible Lewis structures.

Resonance structures are one of the two or more structures for a singlemolecule that cannot be described fully without only one Lewis structure. Aresonance hybrid is the structure that results from resonance in which the “true”Lewis structure is represented by the combination of two or more resonance

structures. The position of electrons of the resonance hybrid, not those of atoms,can be rearranged in different resonance structures.

The electron pair geometry is the overall arrangement of electron pairsaround the central atom while the molecular geometry (of a molecule/ion) is thearrangement of the atoms in space.

< 0.5 nonpolar covalent

0.5 < ΔEN < 2.0 polar covalent

2.0 < ΔEN ionic




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Repulsive forces decrease in the following order:lone pair

vs.lone pair repulsion

>

lone pair

vs.bonding pair repulsion

>

bonding pair

vs.bonding pair repulsion

A polar molecule is has separate centers of positive and negative chargesthat produces a dipole, magnitude given by the dipole moment.

Charge distribution of the molecule is determined by the polarity of amolecule’s bonds and its geometry.

any diatomic molecule - in which and have different electronegativitiesis polar

the polarity of a polyatomic molecule depends on the vector sum of the dipolemoments are to each individual bond

Intermolecular Forces of Attraction (IMFA) are attractions betweenmolecules that account for the excitement of the condensed states of matter (liquid and solid). They are primarily responsible for the bulk properties of matter and are much weaker than chemical bonds

London Dispersion Forces are weak, short-lived interactions resulting fromthe motion of electrons in atoms that are present in all substances. They areinvolved in the creation of instantaneous and induced dipoles. They are namedafter Fritz London who theoretically explained these forces in 1980.

Dipole-dipole forces are forces that act between polar molecules and areabout 1% as strong as covalent bonds. They are effective only when polar molecules are very close together.

Hydrogen bonding is a special type of dipole-dipole interaction that haveattraction between certain molecules greater than can be accounted for byordinary dipole-dipole interactions. This bond is generally 5-10% as strong as

covalent bonds. A common structural feature about hydrogen bonding is that atleast one Hydrogen atom is covalently bonded to a highly electronetagive atom,i.e. nitrogen, oxygen, or fluorine, with at least one unshared electron pair.

Polarizability is a measure of the ease with which the charge distribution canbe distorted by an external magnetic field. In general, heavier atoms or larger molecules tend to have greater polarizabilities which yields stronger Londonforces. Shape is also an important indicator of magnitude of London forces.

Strong IMFA leads to:

high boiling point

high heat of vaporization high melting point

high heat of fusion

high surface tension

high viscosity

low vapor pressure




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States of Matter the physical state at which a substance would normally exist depends on the

attractive forces between molecules called IMFA

Gas particles have no volume, no attraction for each other and in continuousmotion, exerting pressure on its container by colliding on the walls.

In liquids In solids

moving particles crowd together insmall groups

no structure is required groups of particles move past each

other

individual particles can break fromtheir neighbors and join other groups

particles are held in fixed positionby strong forces of attraction

particles packed closely together

in a rigid structure particles are not able to move

from one position to another

individual particles vibrate in their position

Properties of liquids and solids in general

molecules of liquids and solids are touching each other and cannot be pushedmuch closer; nearly incompressible

denser than gases

most substances have density of solids greater than that of liquids (importantexception is water)

if temperature of liquid is lowered low enough, molecules won’t have sufficientenergy to move and can only vibrate

if temperature is lowered very quickly, molecules get stuck in the disorderedarrangement of the liquid

if temperature is lowered slowly, molecules have time to arrange themselves inan ordered structure

Metals consist of the uncombined metallic elements. A metallic substance is alattice of ions within a continuous “sea” of delocalized electrons. Metallic bonding

is the electrical attraction between the positive ions and the delocalizedelectrons.

Ionic substances include compounds of metals with non-metals andammonium compounds. Except for the oxides and hydroxides they are calledsalts. Ionic compounds consist of positive ions and negative ions occupyingalternate positions in a regular lattice. Ionic bonding is the electrical attractionbetween positive and negative ions.

Covalent molecular substances include non-metals and most compoundscontaining only non-metals. they exist in groups of atoms called molecules.Covalent bonding is the electrical attraction between shared electrons and thepositive nuclei of adjacent atoms. A single bond is a shared pair of electrons. In adouble bond, four electrons are shared. In a triple bond, six electrons are shared.

The noble gases exist as atoms. they have similar physical properties tocovalent molecular substances.




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Covalent network substances include a few non-metal elements, such ascarbon and silicon, and a few compounds containing only non-metals, such as

silicon carbide and silicon dioxide. Every atom is covalently bound to other atomsin a lattice.

Property Metallic IonicCovalentMolecular

CoalentNetwork

Melting Point high high low very highElectricalConductivity

Solid conductingnon-

conductingnon-

conductingnon-

conducting

Molten conducting conductingnon-

conducting

non-

conducting

Aqueousinsolubleunless

reactive

conducting if soluble

non-conductingand do not

react

insoluble

Hardness variable very hard soft very hardMalleability malleable very brittle brittle brittle

Substance Property Explanation

Metals

good conductors of electricity

and heat

delocalized electronstransfer charge andthermal energy

high melting point and boilingpoint

strong metallic bondingextending throughout thelattice

dense ions tightly packed in the

lattice

malleable and ductile distortion does not

disrupt the metallicbonding

lustrous

delocalized electrons

cause reflection of light

IonicSubstances

non-conductors of electricitywhen solid

ions firmly bound in thelattice, so no mobilecharged particles

conductors of electricity whenmolten or in aqueous solution

ions are free to move

high melting point and boilingpoint

strong ionic bondingextending throughout thelattice

hard ions strongly bound in

the lattice

brittle distortion causes

repulsion between ionsof like charge




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CovalentMolecular

non-conductors of electricitywhen solid molten or

dissolved in water, unless areaction occurs with water toproduce ions

the molecules areuncharged and electrons

are localized in covalentbonds or on the atoms

low melting point and boilingpoint

soft solids, liquids, or gases

weak forces betweenmolecules

Covalent

Network

non-conductors of electricitywhen solid or molten

electrons localized incovalent bonds or on theatoms

very high melting points strong covalent bonding

extending throughout the

lattice

hard atoms strongly bound in

the lattice

brittle distortion breaks

covalent bonds

Liquids

composed of molecules, atoms, or ions

randomly packed n small groups

amount of free space between particles is quite small the particles are at constant random motion

the particles attract each other

Bulk properties of liquids – variations in the physical properties like boilingpoint, melting point, vapor pressure; arising from the collection of moleculesbrought about by intermolecular forces of attraction that may or may not be inoperation.

Vapor Pressure

pressure exerted by a vapor when in equilibrium with its liquid at a giventemperature

vaporization is a process in which passage of molecules from the surface of liquids to the vapor or gas phase

dynamic equilibrium occurs when opposing processes are going on at thesame time at the same rate

Boiling Point

temperature at which vapor pressure of the liquid is equal to the externalpressure

heat of vaporization is energy required to vaporize a certain amount of liquid

Freezing/Melting Point

temperature at which solid and liquid coexist within the substance

as pressure increases, melting point generally increases with the exception of water

heat of fusion is the energy required to melt a certain solid




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Viscosity

liquids flow because molecules or groups of molecules move past each other

strong intermolecular forces of attraction between molecules would make itmore difficult for molecules or group of molecules to move past each other

increase in temperature lowers viscosity

Surface Tension

force on the surface of the liquid that makes the area of the surface as smallas possible

resistance to an increase in surface area

reason why some insects can walk on water

for a given volume of liquid, the sphere has the smallest surface area

brought about by the difference in the forces between molecules at the surface

and molecules in the bulk of the liquid

Capillary Action

spontaneous rising of liquid in a narrow tube

a consequence of surface tension

raises the surface of H2O in a glass tube having a small more and lowers thesurface of Hg in the same tube

due to the relative strengths of cohesive (IMFA) and adhesive forces

Specific Heat

the amount of heat needed to raise the temperature of one gram of substanceby 1℃

directly related to the strength of IMFA

The heat of vaporization is the quantity of heat that must be absorbed if acertain quantity of liquid is vaporized at a constant temperature.

The heat of fusion is the amount of energy absorbed by a solid to the pointwhere the molecules holding their bonds together break apart and form a liquid

The heat of sublimation is the amount of energy that must be added to asolid at constant pressure in order to turn it directly in to a gas (without passingthrough the liquid phase).

A phase change is a change from one physical state to another accompaniedby a change in energy.

A heating curve is a plot of temperature versus time where energy is addeduniformly and continuously.

A cooling curve is similar to a heating curve but energy is removed at aconstant rate.

A phase diagram is a representation of the conditions (pressure versus time)at which a substance exists in the gas, liquid, and solid state.

The critical point is the highest temperature at which a gaseous substancecan be liquefied, above which a gaseous substance cannot be liquefied nomatter how high the pressure is.

Beyond the critical point, the substance would become a supercritical fluid.The triple point is a point on the phase diagram where the solid state, liquid

state, and gaseous state are present in the substance.




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Gas laws are natural laws governing the physical properties and behavior of gases.Boyle’s Law states that for a fixed amount of gas at a constant temperature,

the volume of the gas is inversely proportional to the gas pressure.Charles’ Law states that the volume of a fixed amount of gas at a constant

pressure is directly proportional to the absolute temperature.Avogadro’s Law states that equal volumes of different gases compared at the

same temperature and pressure contain equal number of molecules; equalnumber of molecules of different gases compared at the same temperature andpressure occupy equal volumes; at a fixed temperature and pressure, the volumeof the gas is directly proportional to the amount of gas

The ideal gas equation is the unifying equation that includes all gas variablesand combines the constants into , the universal gas constant, which is equal

to 0.0821× ×. 1

An ideal gas is made up of gas particles that have no volume, no attractionsfor each other, and in continuous motion, exerting pressure on its container bycolliding with the walls.

At standard temperature and pressure, the volume occupied by one mole of gas with 6.02 × 1023 molecules/atoms is equal to 22.4

.

Dalton’s Law of Partial Pressures

for a mixture of gases in a container, the total pressure exerted is the sum of the pressures that each gas would exert if it were alone

for a mixture of non-reacting gases, the total pressure will be = 1 + 2 +3 + ⋯

assuming that each gas behaves ideally, the partial pressures of each gas

could be expressed as in an ideal gas equation: =

=

Non-ideal gas (Real gases)

show behavior deviating from ideal gases at high pressures, molecules become crowded and repulsive forces among

electrons does not allow the volume of the gas to approach zero

at high pressures, compression and crowding allow for IMFA to be effective,therefore pressure of real gases decrease since collision with walls aredecreased as a result of IMFA

van der Waals equation: +22

− = where and are

specific values for particular gases. The ideal gas equation is corrected for thevolume of the molecules and for the IMFA effect on pressure.

Kinetic Molecular Theory

a gas is composed of very large number of extremely small particles inconstant random straight-line motion

According to your calculator, ≈ 0.08205745867 For Casio − 991 scientific calculators, = CONST27[CONV26] × 1000




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molecules are separated by great distances

molecules collide with one another and with the walls of their container

there are assumed to be no forces between molecules except very brieflyduring collisions

individual molecules may gain or lose energy as a result of collisions

Kinetic Molecular Equation: = 2

3 where denotes pressure,

denotes the number of molecules in a volume, denotes volume, denotes themolecular mass, and denotes the average of the squares of the speed of themolecules.

Diffusion and Effusion

properties related to kinetic molecular theory rates at which diffusion and effusion occur directly proportional to molecular

speed

diffusion is the migration/intermingling of molecules of different substances asa result of random molecular motion

effusion is the escape of gas molecules from their container through a tinyhole

is the root mean square speed which is the square root of the mean of the squares of the speeds of all molecules of the sample

Graham’s Law states that the rates of effusion or diffusion of two different

gases are inversely proportional to the square root of their molar masses.

effusion rate effusion rate =

=

A chemical reaction is a process in which one set of substances calledreactants is converted to a new set of substances called products.

Signs of a chemical reaction

color change formation of a solid (precipitate) within a clear liquid

evolution of gas

evolution/absorption of heat

Chemical Equation

symbolic representation of a chemical reaction

law of conservation of mass necessitates a balanced chemical equation

stoichiometric coefficients are added or manipulated to balance a chemicalequation

to balance chemical equations by inspection, adjust coefficients by trial anderror until a balanced condition is found

the formula of the reactant or product must not be altered to balance theequation




19

Types of Chemical Reactions

combustion is the complete combustion of C, H, and O compounds which

produces CO2 and H2O as the only products decomposition

combination

precipitation (double displacement)

gas-forming reactions

acid-base reactions or neutralization

oxiadation-reduction reactions or RedOx reactions occur when electronsare transferred from one reactant to another

Stoichiometric Proportions – when all the reactants are completely andsimultaneously consumed in mole ratios dictated by the coefficients in a

balanced chemical reactionThe limiting reactant is the reactant that is completely used up on a chemical

reaction and dictates the amount of product formed.The excess reactant is present in more than the stoichiometric proportion

given in a balanced equation.

Rules for determining oxidation number

any atom in its face or elemental state has an oxidation number equal to zero

for monoatomic ions, oxidation umber is equal to the charge of the ion

fluorine, in all its compounds always has an oxidation number of −1 alkali metals, in all their compounds, have an oxidation number of +1

alkaline earth metals, in all their compounds, have an oxidation number of +2

the elements of group 17 (halogens) have an oxidation of −1 in their binarycompounds with a metal

oxygen atoms have an oxidation number of −2 in most of its compoundsexcept in:

its compounds with fluorine, oxygen has a positive oxidation number

peroxides (O22-

)

the superoxide ion, O2-, it has an oxidation number of

−1

2

in most of its compounds, except in hydrides, the oxidation number of hydrogen is +1

in hydrides, where hydrogen is in combination with a less electronegativeatom, each hydrogen atom has an oxidation number of −1

other compounds of complex ions not covered by the above rules areassigned oxidation number such that the sum of the oxidation numbers of allthe atoms in the compound or complex ion is equal to the net charge of thecompound or ion

Potential (°

)

measure of the tendency of the half reaction to occur also called voltage or electromotive force

Reduction Potential

tendency of the species to gain electrons

the more positive the reduction potential, the greater is its tendency to occur,the stronger the species can act as oxidizing agent




20

Oxidation Potential

tendency of the species to lose electrons the more positive the oxidation potential, the greater is its tendency to occur,

the stronger the species can act as reducing agent

Standard Reduction Potential Table

list of oxidizing agents written as reduction half reactions, in the order of increasing strength with their corresponding potentials

determined by comparing with the potential of standard hydrogen electrode,set at standard conditions:

for aqueous solutions, concentration is at 1 molar

for gases, pressure at 1atm and temperature at 25

℃

Cell Potential

sum of the potentials of two half reactions

potential of the overall or net reaction

positive overall cell potential for a reaction indicates that the reaction isspontaneous

for any spontaneous reaction, the stronger reducing agent and the stronger oxidizing agent is on the reactant side

Thermochemistry is a branch of chemistry concerned with heat effectsaccompanying chemical reactions.

A system is a part of the universe we choose to study while the surroundings are the parts of the universe with which the system interacts.

Types of systems:

an open system is where both energy and matter can be transferred betweenthe system and the surroundings

a closed system is where only energy can be transferred between the system

and surroundings but not matter an isolated system is where neither energy nor matter can be exchanged

between the system and the surroundings

Energy transfers are often in the form of heat and work.Heat is the energy transferred between a system and its surroundings as a

result of temperature differences.Work is produced by an action force through a distance.Energy is the capacity to do work; something that matter has that can make

things happen.

Kinetic energy is the energy of an object that is moving. = 2

2 . In solid,

liquid, or gas matter:

individual atomic sized-particles are in constant motion, therefore possesseskinetic energy

for any object, the average kinetic energy of its atomic-sized particles isdirectly proportional to the absolute temperature (in Kelvin) of the object




21

Potential Energy

stored energy due to condition, position, or composition energy that an object has because it is either attracted to or repelled by some

other object

When objects that attract each other are pulled apart, their kinetic energyincreases. When they move toward each other, their kinetic energy decreases.

When objects that repel each other are pushed toward each other, their potential energy increases. When they are moved apart from each other, their potential energy decreases.

Law of Conservation of Energy (First Law of Thermodynamics)

energy can neither be created nor destroyed but can only be transformed fromone form to another

in an isolated system, there is no energy transfer, therefore, the total energy of the system is constant

In almost all chemical reactions there is either absorption or release of energy.Chemical reactions may be classified based on energy of the system:

in an exothermic reaction…

reaction results in evolution of heat

energy of heat flows out of the system

potential energy of the product is less than the potential energy of thereactant

overall potential energy of the system decreases

in an endothermic reaction…

reaction results in absorption of heat

energy of heat flows into of the system

potential energy of the product is greater than the potential energy of thereactant

overall potential energy of the system increases

Enthalpy

change in heat content in a chemical reaction ∆ or change in enthalpy is measured

it is impossible to measure the actual heat content of any particular substance

only the apparent changes in heat content when reactants are transformed toproducts is measured

Total energy change in a reaction: ∆ = °products− °reactants

The heat of formation, denoted by °, is the change in enthalpy that

accompanies the formation of one mole of compound from its elements in their

standard states, i.e. 25℃ at 1atm.

The standard state is the most stable form of the element at conditions 1atm

and 25℃.

The ∆ ° of an element in its standard or most stable form is zero.




22

The spontaneity of reactions make processes occur without outsideintervention. It may be fast or slow.

∆ may indicate of the likelihood of a chemical reaction occurring unassisted(spontaneity of reactions)

in general, exothermic reactions (−∆) are more likely to occur spontaneously

than endothermic reactions (+∆), though there are some exceptions

A characteristic common to all spontaneous processes is an increase in aproperty called entropy. Entropy, denoted by , is the measure of randomnessor disorder. Applying it to molecules, solid < iquid ≪ gas.

The second law of thermodynamics (universal entropy) states that in anyspontaneous processes, there is always an increase in the entropy of the

universe.

If univ is…

positive, then entropy of the universe increases, and the process isspontaneous in the direction written

negative, then entropy of the universe decreases, and the process isspontaneous in the opposite direction

zero, then the process has no tendency to occur and the system is inequilibrium

Disorder something that brings about disorder is more likely to occur than something

that brings about order

close relationship between randomness and statistical probability

laws of chance sometimes hidden by the changes in energy

if energy changes could be ignored or made less important, statisticalprobability would become the primary driving force for change

Enthalpy and Entropy

two factors that determine whether or not a given physical or chemical eventwill be spontaneous

may work together or act in opposition

∆ is dependent on temperature, and related by the Gibbs Free EnergyEquation, = −, where is the free energy, is the entropy of the system,and is the absolute temperature in Kelvin. At constant temperature, ∆ = ∆ −∆. At constant temperature and pressure, a process is spontaneous in thedirection in which free energy ∆ decreases.

To predict spontaneity of processes or reactions, use two functions:

∆univ applies to all processes; a process is spontaneous if

∆univ is positive

∆ applies only if at constant temperature and pressure if ∆ is negative, the reaction is spontaneous as written

if ∆ is positive, the reaction is spontaneous in reverse

if ∆ is equal to zero, the reaction is at equilibrium

When a reaction is…

exothermic ∆ < 0




23

accompanied by an increase in entropy ∆ > 0

∆will always be negative regardless of the value of the absolute temperature

change will occur spontaneously at all temperatures endothermic ∆ > 0

accompanied by an increase in entropy ∆ < 0

∆ will always be positive regardless of the value of the absolute temperature

change will always be non-spontaneous at all temperatures

when ∆ and ∆ have the same signs, the temperature becomes critical

Implications to the second law of thermodynamics with respect to the presentproblems of:

environmental pollution

pollution is the scattering of undesirable substances throughout theenvironment

a direct result of our efforts to create an orderly world

accompanied by an increase in entropy

pollution can never really be eliminated

energy crisis there is really no lack of energy

problems arise from the unavailability of energy

in our day-to-day life, we do not consume energy; we merely convert it froma usable form to an unusable form

more correctly, the search for energy is a search for usable forms of energy:

stored in the bonds of chemical fuels

in nuclear fuels

provided by sun’s rays

Chemical Kinetics is the study of rates of chemical reactions, rate laws, andreaction mechanism.

Collision Theory (Arrhenius Theory) states that for a chemical reaction tooccur:

reacting particles must collide effectively to enable outer shell electrons tointeract

collision must be with enough force to overcome the repulsive forces betweenelectrons surrounding the nuclei of the atoms

collision of particles must be in the correct orientation

atoms and electrons rearrange, bonds are broken and new bonds are formedin the production of new substances during collision

Factors affecting rates of reaction:

nature of reacting substances depend on specific bonds involved; a morestable molecule has a lower rate of reacting

∆ > 0 ∆ < 0

∆ > 0 spontaneous only at high

temperatures spontaneous at all

temperatures

∆ < 0 not spontaneous at all

temperatures spontaneous only at low

temperatures




24

concentration of the reactants – rates increase with higher concentration of reactant; more molecules yield more frequent collisions

state of subdivision of the reactant – rates increase with a higher surface area presence of a catalyst – catalyst decreases the activation energy,

consequently hastening the rate of reaction

temperature – generally, a high temperature increases the rates of reaction

Solubility is the maximum amount of substance that dissolves in a given

quantity of solvent at a given temperature to form a saturated solution.

Before the formation of a solution, both solute and solvent have an ∆H > 0. After the formation of the solution, the resulting ∆H < 0. Also, ∆Hsolution = ∆H1 +

∆H2 +

⋯+

∆Hn

Factors affecting solubility:

nature of solute and solvent – only substances with similar polarity will dissolveeach other

pressure – a high pressure will increase the solubility of gases in liquids

temperature

a higher temperature will have a decrease in the solubility of gases in liquids

a higher temperature will have a higher rate of solution of solids

a higher temperature will increase the solubility of most solids in liquids

Factors affecting rate of dissolution: stirring (agitation) will increase frequency of interaction between solvent and

solute particles

state of subdivision or particle size of solute – a finely divided solute has largesurface area, allowing more contact surface with solvent molecules

temperature – increasing the temperature increases the average kineticenergy of solute and solvent particles, therefore increasing frequency of interactions

Quantitative was of expressing concentration:

solutions provide a fluid medium that allows particles to collide and react

quantitative measurements of reactants and products in a reaction in solutionis made possible through stoichiometry

it is performed to be able to express quantities of solutes in reactions

Expressions of concentration in solutions as ratios:

molar concentration or molarity

denoted by M =nsolute

Vwhere volume is expressed in liters

the unit of molarity is molar, denoted by M

this expression of concentration is usually used in determining molequantities of reactants and products

molal concentration or molality denoted by b =

nsolute

msolvent

2where mass is expressed in kilograms

the unit of molality is molal, denoted by m

2The symbol for molality is interchangeable between b and m. It is replaced by b

in this case to disambiguate the symbol for molality and mass.




25

molar fraction

denoted by

=

nsubstance

n

1 + 2 + ⋯+ = 1 percent concentration

%w/w =msolute

msolution

%v/v =Vsolute

Vsolution

%w/v =msolute

Vsolution

parts per million (ppm) and parts per billion (ppb)

ppm%w/w =mg solute

kg solution

ppm%w/v =mg solute

Lsolution

ppm%w/v = μgsolute

mL solution

ppb%w/w =μgsolute

kg solution

ppb%w/v =μgsolute

Lsolution

Stock solutions are solutions that have high concentration and are preparedin the laboratory. Working solutions are dilute solutions prepared from stocksolutions.

To make dilute solutions from concentrated solutions, use the formula

1

1 =

2

2.

Stoichiometry of reactants in solutions:

calculations performed are similar to pure substances taking part in a reaction

the only difference is that after finding the number of moles needed, thevolume containing these number of moles is calculated

stoichiometric coefficients provide key in calculating the quantities of chemicals involved in the reaction

Colligative properties of aqueous solutions:

physical properties of solution different from the solvent

dependent on the relative amounts of the components

more dilute solutions approach properties of solvento vapor pressure loweringo vapor pressure of solution is lower than that of pure solvento as the concentration of solute increases, the decrease of the vapor pressure

difference between pure solvent and solution increaseso Raoult’s Law describes vapor pressure lowering in an equation:

Σ = χAPA∗ + χBPB

∗ o boiling point elevationo consequence of vapor pressure loweringo boiling point of solution is higher than that of the pure solvent

o ∆ = where ∆ is the boiling point elevation, is the boiling pointelevation constant of water (0.52℃/), and is the molality of the solution

o freezing point depressiono freezing point of solution is lower than that of solvento physically may be explained by the inability of the solvent molecules to

arrange into the open structure of its solid form due to obstruction caused bysolute molecules at its usual freezing temperature




26

o a much lower temperature is needed to further compress the solventmolecules together and for the hydrogen bonding to take effect among the

solvent moleculeso ∆ = where ∆ is the freezing point depression, is the freezing

point elevation constant of water (1.86℃/), and is the molality of thesolution

o osmotic pressureo pressure exerted in a solution to hold off or stop osmosiso osmosis is process which particles in solution selectively move through a

semi-permeable membrane

Chemical Equilibrium

initially, reactants present at definite concentrations as reaction proceeds, concentrations of reactants decreases; those of

products increase

after a time, concentrations level off and become constant, undergoing a stateof chemical equilibrium

Characteristic features of systems at equilibrium:

the system does not gain matter from the surroundings nor lose matter to thesurroundings, which means the equilibrium system is a closed system

the system is dynamic, i.e. the opposite processes occur at the same time

measureable properties of the system remain constant, i.e. the oppositeprocesses occur at the same rate

at a given temperature, the extent to which reactions occur before equilibriumis attained can be indicated by a constant related to the concentrations of reacting substance

Reverse reactions are reactions where conditions allowing the reactants toform the products also permit the products to reform the reactions. Irreversiblereactions are reactions where products cannot give back the reactants under thegiven conditions.

Equilibrium Changes: chemical equilibrium represents a balance between forward and reverse

reactions

changes in experimental conditions may disturb the balance

shift the position of equilibrium so that more or less of the desired product isformed

Le Chatelier’s Principle (1885)

“when a stress is applied to a system in equilibrium a chemical change occursin the direction that relieves the stress and brings the system to equilibrium

again” – Henry Louis Le Chatelier suggests an outcome

offers no explanation on the effect of changes

does not produce numerical values

Equilibrium changes may involve any of the following:

changing the concentration of a reactant or product




27

changing the pressure of gaseous systems

changing the temperature

Changing the concentration of a reactant or product:

if a system is at equilibrium and the concentration of a reactant is increased sothat the system is no longer at equilibrium, more reaction will occur in thedirection that reduces the concentration of that reactant

Changing the pressure of gaseous systems:

the simplest way to analyze the effects of a volume change on an equilibriumsystem is to count the number of molecules of gaseous substances on bothsides of the equation

an increase in pressure, or decrease in volume, always drives the reaction in

the direction of the fewest number of molecules of gas reaction involving liquids or solids have no way of counteracting pressure

changes

addition of inert gas to a system in equilibrium will have no effect on theposition of equilibrium; individual concentrations and partial pressures of reacting gases remain unchanged

Changing the temperature: to predict the effect of temperature change…

treat heat as a reactant (in an endothermic change) or as a product (in anexothermic change)

predict the direction of shift as if an actual reactant or product is added or removed

Law of Mass Action (1864)

proposed by the Norwegian chemists Cato Maximilian Guldberg and Peter Waage

expresses the relationships between the concentrations of reactants andproducts at equilibrium in any reaction

describes equilibrium condition in a reaction: aA + bB → cC+dD

Equilibrium Constant

numerical value obtained when actual equilibrium concentrations aresubstituted into the equilibrium constant expression

value of depends on what the reaction is, how the reaction is written, andtemperature

=

A large equilibrium constant favors the products strongly and the reaction goesessentially to completion. A small equilibrium constant favors the reactantsstrongly and the reaction proceeds hardly at all toward completion. Anequilibrium constant equal to or near 1 is at equilibrium, when quantities of

reactants and products are comparable.

A homogeneous equilibrium is an equilibrium in which the reaction speciesare in the same phase while a heterogeneous equilibrium is an equilibrium inwhich the reaction species are in different phases.




28

Rules for writing equilibrium constant expressions

the unit of concentration usually used for species in condensed phases are in

mol and for those in gaseous phases, either mol or atm is used concentrations of pure solids, pure liquids (in heterogeneous equilibria) and

solvents (in homogeneous equilibria) do not appear in the equilibrium constantexpression

the equilibrium constant is treated as a dimensionless quantity

in quoting a value for the equilibrium constant, the balanced equation and the

temperature must be specified

when the equation for a reversible reaction is written in the opposite direction,the equilibrium constant is the reciprocal of the original equilibrium constant

In calculating for the value of the equilibrium constant:

of reverse reaction is −1

multiplying the coefficients of balanced equation by a factor, , means that theoriginal equilibrium constant is raised to the th power

The is an expression of in concentration while the is the expression

of in pressure, calculated as = ∆ .

Arrhenius definition of acids and bases:

first proposed in 1884 and is the oldest, most restrictive and simplest definition

an Arrhenius acid is a neutral molecule that dissolves in water to give H+ ionsand an anion and it increases the H+ of water

an Arrhenius base is a neutral molecule that dissociates in water to give OH−

ions and a cation and it increases the OH− of water

an acid-base reaction in the Arrhenius sense is the coming together of H+ andOH− to form water resulting in the neutralization of the acid and the base

acid + base → salt + water

Brønsted-Lowry definition of acids and bases:

suggested independently by Brønsted and Lowry in 1923 and is more general

than the Arrhenius definition a Brønsted-Lowry acid is a substance that donates a proton

a Brønsted-Lowry base is a substance that accepts a proton

acid + base → conj. acid + conj. base As to whether it is the forward or backward reaction that is going to be favored

depends upon the relative strengths of the pairs of reacting cid and base. Thestrength of an acid depends upon its tendency to give up a proton, while thestrength of a base depends on its tendency to accept a proton. The dissociationconstant in water is frequently used as a measure of the relative strengths of acids and bases.

Strong acids and bases are those that almost completely ionize in water with

> 2. For a strong acid, the only acid present in the solution is H3O+. The onlybase present in solutions of a strong base is OH−

Weak acids and bases have their equilibria toward the left. These have smallacidity constants and basicity constants, respectively.




29

Lewis definition of acids and bases:

proposed by Lewis in 1923 and it is the broadest definition and includes all

other definitions a Lewis acid is a substance that accepts an electron pair and it must have a

vacant orbital which it can use to form a covalent bond with the electron pair of the base; examples:

molecules with an atom having less than an octet of electrons

molecules in which the central atom has available d orbitals and mayacquire more than an octet of electrons

molecules with multiple bonds between atoms of dissimilar electronegativity

cations

a Lewis base is a substance that donates an electron pair and must have anavailable electron pair; examples:

molecules with an atom having an unshared electron pair(s)

anions

any reaction that leads to the formation of a coordinate covalent bond is aLewis acid-base reaction

A buffer is a solution that is able to absorb small additions of concentratedacids and bases without giving rise to a significant change in the pH of thesolution.

Nuclear Chemistry study of nuclear reactions and their uses in chemistry

deals with changes in matter originating in the nucleus of an atom

involves changes in the atomic number and/or mass number of the reactant

Radioactivity is the spontaneous disintegration of an unstable atomic nucleuswith accompanying emission of radiation in order to form a more stable species.

A nuclide is a nucleus with a specified mass number, A; number of protons, Z;and number of neutrons.

Isotopes are atoms of the same element where the nuclei contain different

number of neutrons. A nucleon is a particle that makes up the nucleus, i.e. the protons and the

neutrons.

Nuclear Particle Symbol Alpha (Helium) He2

4 or α24

Beta− (electron) β−10 or e−1

0

Beta+ (positron) β10 or e1

0 Neutron n0

1 Proton p1

1 or H11

Gamma γ0

0

or γ

Nuclear Binding Energy

energy released in a nuclear fission or fusion reaction

this energy is very large and can be harnessed positively (nuclear power plants) or destructively (atom bomb or H-bomb)

dependent on the mass defect which is highest observed in bismuth




30

nuclear stability is dependent on the neutron:proton ratio

Characteristic of the Nuclear Binding Energy: greater than electromagnetic and gravitational forces

short range and effective only at very short distance

Nuclear Stability depends on:

ratio of neutrons to protons (belt of stability)

concept of complete nuclear shell or closed shell configuration (magicnumbers)

odd-even number of nucleons (an even number is more stable)

The belt of stability is a general guide to the area within

which all stable nuclei are found.

Odd-even combination and nuclear stabilityproton neutron number of stable nuclides

even even 163

even odd 55

odd odd 50odd even 4

Types of nuclear reactions:

alpha decay usually emitted by heavy nuclei

as nuclei becomes larger, protons increase, proton-proton repulsionbecomes larger, and the nuclear binding force becomes insufficient to holdall protons together

tend to reduce nucleons to become stable by emitting an α particle, similar

to a He nuclide

XZA → JZ−2

A−4 + He24

beta decay (electron emission)

usually occurs when neutrons are in excess, then they are transformed intoprotons with an emission of

β−

electrons are produced as a nuclear reaction occurs

n01 → H1

1 + e−11

beta decay (positron emission)

usually occurs when neutrons are in excess, then they are transformed intoprotons with an emission of β+

positrons are produced as a nuclear reaction occurs

p11 → n0

1 + e10

electron capture or -capture

usually happens when protons are in excess

nuclear stability is achieved by capturing one of the inner electrons

converting a proton to a neutron energy in the form of x-rays are emitted because outer electrons in the

higher energy levels fill up the vacant lower energy level left by the capturedelectrons

p11 + e−1

1 → n01 + γ

Magic Numbers

proton neutron2 2

8 8

20 20

28 2850 50

82 82

114 126

184




31

gamma emission

high energy photons or radiation similar to x-rays but shorter wavelength,

high frequency, and high penetration no mass so the A and Z of nucleus remain unchanged

energy changes that accompanies almost all other radioactive emissionsalthough not represented in nuclear reactions

Nuclear Fission

heavy nucleus splits into two or more lighter nuclei

occurs when heavy nuclei are struck with projectiles or bullets

Nuclear Fusion

nuclei of light elements are made to combine to form heavier nuclei

fusion reaction takes place only at very high temperatures called ignitiontemperatures which can be supplied y an atom bomb

more energetic than fission reaction but difficult to harness

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[Notes]CHEM15.0 - Fundamentals of Chemistry

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