[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
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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
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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
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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.
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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
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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
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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.
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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
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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
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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.
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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.
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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
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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
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CHEM 15.0 Notes by F5XS Fundamentals of Chemistry
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