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General ChemistryGeneral ChemistryAtomic Structure & the Periodic TableAtomic Structure & the Periodic Table Chemical Bonding Chemical Bonding

Introduction to Chemical BondingIntroduction to Chemical Bonding

The Ionic BondThe Ionic Bond

The Covalent BondThe Covalent Bond

The Metallic BondThe Metallic Bond

Intermolecular Attractive ForcesIntermolecular Attractive Forces Structure and ShapeStructure and Shape StoichiometryStoichiometry Functional Group (Biology)Functional Group (Biology)

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ATOMIC STRUCTUREATOMIC STRUCTUREDefinition of Chemistry:

The study of the properties, composition, andSTRUCTURESTRUCTURE of matter, the physical and chemical changes it undergoes, and the energyliberated or absorbed during those changes.

The foundation for the STRUCTURESTRUCTURE of inorganicmaterials is found in the STRUCTURESTRUCTURE of the atom.

Atomic Structure

Molecular Structure

Bulk Structure

Material PropertiesMaterial Properties

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ATOMIC STRUCTUREATOMIC STRUCTUREHistorical Development:

Greek Concepts of MatterGreek Concepts of Matter

Aristotle - Matter is continuous, infinitelydivisible, and is composed of only 4 elements:

Earth, Air, Fire, and WaterEarth, Air, Fire, and Water

Won the philosophical/political battle. Dominated Western Thought for Centuries. Seemed very “logical”. Was totally WRONG!!WRONG!!

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ATOMIC STRUCTUREATOMIC STRUCTURE

The “Atomists” (DemocritusDemocritus, Lucippus,Epicurus, et. al.) - Matter consists ultimatelyof “indivisible” particles called “atomos” thatcanNOT be further subdivided or simplified.If these “atoms” had space between them,nothing was in that space - the “void”.

Lost the philosophical/political battle. Lost to Western Thought until 1417. Incapable of being tested or verified. Believed the “four elements” consisted of “transmutable” atoms. Was a far more accurate, though quite imperfect “picture” of reality.

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ATOMIC STRUCTUREATOMIC STRUCTUREModern Concepts of MatterModern Concepts of Matter

John Dalton (1803) - An atomist who formalizedthe idea of the atom into a viable scientific theoryin order to explain a large amount of empiricaldata that could not be explained otherwise.

Matter is composed of small “indivisible” particles called “atoms”. The atoms of each element are identical to each other in mass but different from the atoms of other elements. A compound contains atoms of two or more elements bound together in fixed proportions by mass.

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ATOMIC STRUCTUREATOMIC STRUCTURE A chemical reaction involves a rearrangement of of atoms but atoms are not created nor destroyed during such reactions.

Present Concepts - An atom is an electricallyneutral entity consisting of negatively chargedelectrons (e-) situated outside of a dense, posi-tively charged nucleus consisting of positivelycharged protons (p+) and neutral neutrons (n0).

ParticleParticle ChargeCharge MassMassElectronElectron - 1 - 1 9.109 x 10 9.109 x 10 -28 -28 ggProtonProton +1 +1 1.673 x 10 1.673 x 10 -24 -24 ggNeutronNeutron 0 0 1.675 x 10 1.675 x 10 -24 -24 gg

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ATOMIC STRUCTUREATOMIC STRUCTURE

e- e-p+no

no p+

NucleusNucleus

Electron CloudElectron Cloud

Model of aModel of aHelium-4Helium-4

((44He) atomHe) atom

How did we get this concept? - This portion of ourprogram is brought to you by:

Democritus, Dalton, Thompson, Planck, Einstein, Millikan, Democritus, Dalton, Thompson, Planck, Einstein, Millikan, Rutherford, Bohr, de Broglie, Heisenberg, Schrödinger, Rutherford, Bohr, de Broglie, Heisenberg, Schrödinger, Chadwick, and many others.Chadwick, and many others.

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ATOMIC STRUCTUREATOMIC STRUCTUREDemocritus - First atomic ideasDalton - 1803 - First Atomic Theory J. J. Thompson - 1890s - Measured the charge/mass

ratio of the electron (Cathode Rays)

+

Anode

_

Cathode

Electric FieldSource (Off)

FluorescentMaterial

With the electric field off, the cathode ray is not deflected.With the electric field off, the cathode ray is not deflected.

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ATOMIC STRUCTUREATOMIC STRUCTURE

Cathode

Anode Electric FieldSource (On)

FluorescentMaterial

-

+ +

-

With the electric field on, the cathode ray is deflectedWith the electric field on, the cathode ray is deflectedaway from the negative plate. The stronger the electricaway from the negative plate. The stronger the electricfield, the greater the amount of deflection.field, the greater the amount of deflection.

Cathode

Anode

-

+Magnet

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ATOMIC STRUCTUREATOMIC STRUCTUREWith the magnetic field present, the cathode ray isWith the magnetic field present, the cathode ray isdeflected out of the magnetic field. The stronger thedeflected out of the magnetic field. The stronger themagnetic field, the greater the amount of deflection.magnetic field, the greater the amount of deflection.

e/m = E/He/m = E/H22rr

e = the charge on the electronm = the mass of the electronE = the electric field strengthH = the magnetic field strengthr = the radius of curvature of the electron beam

Thompson, thus, measured the charge/mass ratioThompson, thus, measured the charge/mass ratioof the electron - of the electron - 1.759 x 101.759 x 1088 C/g C/g

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ATOMIC STRUCTUREATOMIC STRUCTURESummary of Thompson’s Findings:

Cathode rays had the same properties no matterCathode rays had the same properties no matter what metal was being used.what metal was being used.

Cathode rays appeared to be a constituent of allCathode rays appeared to be a constituent of all matter and, thus, appeared to be a “sub-atomic”matter and, thus, appeared to be a “sub-atomic” particle.particle.

Cathode rays had a negative charge.Cathode rays had a negative charge.

Cathode rays have a charge-to-mass ratioCathode rays have a charge-to-mass ratio of 1.7588 x 10of 1.7588 x 1088 C/g. C/g.

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ATOMIC STRUCTUREATOMIC STRUCTURER. A. Millikan - Measured the charge of the electron.

In his famous “oil-drop” experiment, Millikan was able toIn his famous “oil-drop” experiment, Millikan was able todetermine the charge on the electron independently of itsdetermine the charge on the electron independently of itsmass. Then using Thompson’s charge-to-mass ratio, hemass. Then using Thompson’s charge-to-mass ratio, hewas able to calculate the mass of the electron.was able to calculate the mass of the electron.

e = 1.602 10 x 10e = 1.602 10 x 10-19-19 coulomb coulombe/m = 1.7588 x 10e/m = 1.7588 x 1088 coulomb/gram coulomb/gramm = 9.1091 x 10m = 9.1091 x 10-28 -28 gramgram

Goldstein - Conducted “positive” ray experiments thatlead to the identification of the proton. The chargewas found to be identical to that of the electron and

the mass was found to be 1.6726 x 101.6726 x 10-24-24 g. g.

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ATOMIC STRUCTUREATOMIC STRUCTUREErnest Rutherford - Developed the “nuclear” modelof the atom.

The Plum Pudding Model of the atom:The Plum Pudding Model of the atom:

- - - - - - - - - - - - - - -+

+ +

+++

+

++

+ A smeared out “pudding”of positive charge withnegative electron “plums”imbedded in it.

The Metal Foil Experiments:The Metal Foil Experiments:

RadioactiveMaterial inPb box.

MetalFoil

FluorescentScreen-particles-particles

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ATOMIC STRUCTUREATOMIC STRUCTUREIf the plum pudding model is correct, then all ofthe massive -particles should pass right throughwithout being deflected.

In fact, most of the In fact, most of the - particles DID pass right - particles DID pass rightthrough. However, a few of them were deflected atthrough. However, a few of them were deflected athigh angles, disproving the “plum pudding” model.high angles, disproving the “plum pudding” model.

Rutherford concluded from this that the atom con-Rutherford concluded from this that the atom con-sisted of a very dense nucleus containing all of the sisted of a very dense nucleus containing all of the positive charge and most of the mass surrounded bypositive charge and most of the mass surrounded byelectrons that orbited around the nucleus much aselectrons that orbited around the nucleus much asthe planets orbit around the sun.the planets orbit around the sun.

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ATOMIC STRUCTUREATOMIC STRUCTUREAssignment:Assignment:Assume the diameter of the nucleus of a hydrogenatom is 1 x 10 -13 cm and the diameter of the atomis 1 x 10 -8 cm.

1. Calculate the volume of the nucleus and the volume of the atom in cm3 .

2. Calculate the volume of empty space in the atom.

3. Calculate the ratio of the volume of the nucleus to volume of the whole atom.

4. Calculate the density of the nucleus if the proton’s mass is 1.6726 x 10-24 g

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ATOMIC STRUCTUREATOMIC STRUCTUREProblems with the Rutherford Model:Problems with the Rutherford Model:

It was known from experiment and electromagnetictheory that when charges are accelerated, theycontinuously emit radiation, i.e., they loose energycontinuously. The “orbiting” electrons in the atomwere, obviously, not doing this.

The atoms were NOT collapsing.

Atomic spectra and blackbody radiation were known to be DISDIScontinuous.

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ATOMIC STRUCTUREATOMIC STRUCTUREAtomic Spectra - Atomic Spectra - Since the 19th century, it hadSince the 19th century, it hadbeen known that when elements and compoundsbeen known that when elements and compoundsare heated until they emit light (glow) they emit are heated until they emit light (glow) they emit that light only at discrete frequencies, giving a that light only at discrete frequencies, giving a line spectrumline spectrum..

++

--

HydrogenGas Line Spectrum

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ATOMIC STRUCTUREATOMIC STRUCTUREWhen white light is passed through a sample ofWhen white light is passed through a sample ofthe vapor of a substance, only discrete frequenciesthe vapor of a substance, only discrete frequenciesare absorbed, giving an are absorbed, giving an absorption ban spectrumabsorption ban spectrum..These frequencies are identical to those of the These frequencies are identical to those of the line spectrum of the same element or compound.line spectrum of the same element or compound.

For hydrogen, the spectroscopists of the 19thCentury found that the lines were related by the Rydberg equation:

c = R[(1/mc = R[(1/m22) - (1/n) - (1/n22)] )]

frequency

c = speed of lightR = Rydberg Constantm = 1, 2, 3, ….

n = (m+1), (m+2), (m+3), ….

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ATOMIC STRUCTUREATOMIC STRUCTUREMax Planck - In 1900 he was investigating the nature of black body radiation and tried to interpret hisfindings using accepted theories of electromagneticradiation (light). He was NOT successful since thesetheories were based on the assumption that light hadWAVE WAVE characteristics.

To solve the problem he postulated that light wasemitted from black bodies in discrete packets hecalled “quanta”. Einstein later called them“photons”. By assuming that the atoms of the blackbody emitted energy only at discrete frequencies, hewas able to explain black body radiation.

E = hE = h

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ATOMIC STRUCTUREATOMIC STRUCTUREBoth spectroscopy and black body radiationBoth spectroscopy and black body radiationindicated that atoms emitted energy only at indicated that atoms emitted energy only at discrete frequencies or energies rather thandiscrete frequencies or energies rather thancontinuously.continuously.

Is light a particle or a wave??Is light a particle or a wave??

Why do atoms emit only discrete energies?Why do atoms emit only discrete energies?

What actually happens when light interactsWhat actually happens when light interactswith matter?with matter?

What was wrong with Rutherford’s Model?What was wrong with Rutherford’s Model?

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ATOMIC STRUCTUREATOMIC STRUCTURENiels Bohr - Bohr corrected Rutherford’s modelof the atom by formulating the following postulates:

Electrons in atoms move only in discrete orbitsaround the nucleus.

When in an orbit, the electron does NOT emitenergy.

They may move from one orbit to another but areNEVER residing in between orbits.

When an electron moves from one orbit toanother, it absorbs or emits a photon of light with aspecific energy that depends on the difference inenergy between the two orbits.

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ATOMIC STRUCTUREATOMIC STRUCTURE

+

LymanSeries

BalmerSeries

PaschenSeries

The Bohr Model of the AtomThe Bohr Model of the Atom

(Visible)

(IR)

(UV)

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ATOMIC STRUCTUREATOMIC STRUCTURE The lowest possible energy state for an electronis called the GROUND STATEGROUND STATE. All other statesare called EXCITED STATESEXCITED STATES.

EEnn = (- 2.179 x 10 = (- 2.179 x 10-18-18 J)/n J)/n22

EEphotonphoton = E = Ehighhigh - E - Elowlow

EEphotonphoton = [(- 2.179 x 10 = [(- 2.179 x 10-18-18 J)/n J)/n22highhigh]]

-[(- 2.179 x 10-[(- 2.179 x 10-18-18 J)/n J)/n22lowlow]]

= - 2.179 x 10= - 2.179 x 10-18-18 J[(1/n J[(1/n22highhigh) - (1/n) - (1/n22

lowlow)])]Does this equation look familiar?Does this equation look familiar?

c = R[(1/mc = R[(1/m22) - (1/n) - (1/n22)])]

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ATOMIC STRUCTUREATOMIC STRUCTURENiels Bohr won the Nobel Prize for his work. However, the model only worked perfectly forhydrogen. What about all of those other elements??What about all of those other elements??

Louis de Broglie - Thought that if light, which wasthought to have wave characteristics, could also haveparticle characteristics, then perhaps electrons, whichwere thought to be particles, could have characteristicsof waves.

h/mvh/mv

An electron in an atom was a “standing wave”!An electron in an atom was a “standing wave”!

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ATOMIC STRUCTUREATOMIC STRUCTURE

Werner Heisenberg - Developed the “uncertainty”principle: It is impossible to make simultaneous andIt is impossible to make simultaneous andexact measurements of both the position (location)exact measurements of both the position (location)and the momentum of a sub-atomic particle such asand the momentum of a sub-atomic particle such asan electron.an electron.

((x)(x)(p) p) h/2 h/2

Our knowledge of the inner workings of atoms andmolecules must be based on probabilities ratherthan on absolute certainties.

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ATOMIC STRUCTUREATOMIC STRUCTUREErwin Schrödinger - Developed a form of quantummechanics known as “wave mechanics”.

HHEE

H = Hamiltonian operatorE = Total energy of the systemWave function

[(-h2)/(82m)]2 - [e2/r] = E

This is simply a quantum mechanical statement of the Lawof Conservation of Energy

Kinetic EnergyKinetic Energy TermTerm

Potential EnergyPotential Energy TermTerm

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ATOMIC STRUCTUREATOMIC STRUCTUREOf the numerous solutions to the Schrödinger equationfor hydrogen, only certain ones are allowed due to thefollowing boundary conditions:

, the wave function, must be continuous and finite. It must be single-valued at all points (There can’t betwo different probabilities of finding an electron at onepoint in space). The probability of finding the electron, 2, somewherein space must = 1.

- +

2dxdydz = 1

Y has many values that meet these conditions. They areY has many values that meet these conditions. They arecalled “orbitals”.called “orbitals”.

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ATOMIC STRUCTUREATOMIC STRUCTUREWave Function - A mathematical function associatedwith each possible state of an electron in an atom ormolecule.

It can be used to calculate the energy of anelectron in the state

the average and most probable distance from thenucleus

the probability of finding the electron in anyspecified region of space.

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ATOMIC STRUCTUREATOMIC STRUCTUREQuantum Numbers:

Principle Quantum Number, n - Principle Quantum Number, n - An integergreater than zero that represents the principleenergy level or “shell” that an electron occupies.

EnergyEnergy # of orbitals# of orbitalsnn LevelLevel ShellShell nn22

11 1st 1st K K 1122 2nd 2nd L L 2233 3rd 3rd M M 9944 4th 4th N N 16 16etc. etc. etc. etc.

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ATOMIC STRUCTUREATOMIC STRUCTUREAzimuthal Quantum Number, l - Azimuthal Quantum Number, l - The quantum number that designates the “subshell” an electronoccupies. It is an indicator of the shape of an orbitalin the subshell. It has integer values from 0 to n-10 to n-1.

l = 0, 1, 2, 3, …, n - 1l = 0, 1, 2, 3, …, n - 1

s p d fs p d f

Magnetic Quantum Number, mMagnetic Quantum Number, mll - - The quantum

number that determines the behavior of an electronin a magnetic field. It designates the the orbitalorbital andhas integer values from -l to +l including 0-l to +l including 0.

mmll = -l, …, -3, -2, -1, 0, +1, +2, +3, …, +l = -l, …, -3, -2, -1, 0, +1, +2, +3, …, +l

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ATOMIC STRUCTUREATOMIC STRUCTUREOrbitalOrbital # of# of

nn l Name ml Name mll Orbitals Orbitals

11 00 1s 1s 0 0 1 122 00 2s 2s 0 0 1 1 1 2p1 2p -1, 0, +1 -1, 0, +1 3 333 00 3s 3s 0 0 1 1 1 3p1 3p -1, 0, +1 -1, 0, +1 3 3

22 3d 3d -2, -1, 0, +1, +2 -2, -1, 0, +1, +2 5 5etc.etc. etc.etc. etc. etc. etc.etc. etc. etc.

Spin Quantum Number, mSpin Quantum Number, mss - - The quantum number

that designates the orientation of an electron in a magnetic field. It has half-integer values, +½ or -½.+½ or -½.

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ATOMIC STRUCTUREATOMIC STRUCTURESo what do atoms look like?So what do atoms look like?

A. Interpretation of : The probabilityprobability of findingan electron in a small volume of space centered around some point is proportional to the value ofat that point.

B. Electron Probability Density vs. r

C. Dot Density Representation: Imagine super-imposing millions of photographs taken of an electron in rapid succession.

D. Radial Densities

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Electron Configuration

A. Many-electron atom: An atom that containstwo or more electrons.

B. Problems with the Bohr model:

1. It “assumed” quantization of the energylevels in hydrogen.

2. It failed to describe or predict the spectraof more complicated atoms.

ATOMIC STRUCTUREATOMIC STRUCTURE

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C. What are the differences in electron energylevels in hydrogen vs. more complicated atoms?

1s

2s 2p

3s 3p 3d

Ground State Hydrogen AtomGround State Hydrogen Atom

ATOMIC STRUCTUREATOMIC STRUCTURE

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H

1s

2s 2p

Li

1s

2s2p

Splitting of the DegeneracySplitting of the Degeneracy

ATOMIC STRUCTUREATOMIC STRUCTURE

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1. In hydrogen, all subshells and orbitals in agiven principal energy level have the same energy.They are said to be DegenerateDegenerate.

2. In many-electron atoms, s-orbitals have lowerenergy than p-orbitals which have lower energythan d-orbitals which have lower energy than f-orbitals, etc., etc.

3. Reason: Complex electrostatic interactions.

Splitting of the DegeneracySplitting of the Degeneracy

ATOMIC STRUCTUREATOMIC STRUCTURE

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+-

Hydrogen ++

- -

Helium

+++

Lithium

- --

A. Shielding Effect - A decrease in the nuclear forceof attraction for an electron caused by the presenceof other electrons in underlying orbitals.

B. Effective Nuclear Charge - A positive chargethat may be less than the atomic number. It is thecharge “felt” by outer electrons due to shielding byelectrons in underlying orbitals.

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The Pauli Exclusion Principle - No two electron inNo two electron inthe same atom can have the same four quantumthe same atom can have the same four quantumnumbers.numbers.

H + e- H -

QuantumQuantum Electron 1Electron 1 Electron 2Electron 2NumberNumber nn 11 11 ll 00 00

mmll 00 00

mmss +1/2 +1/2 -1/2 -1/2

ATOMIC STRUCTUREATOMIC STRUCTURE

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The Aufbau Principle - A procedure for “building up”the electronic configuration of many-electron atomswherein each electron is added consecutively to thelowest energy orbital available, taking into accountthe Pauli exclusion principle.

Order of Filling - 1s1s 2s2s 2p2p 3s3s 3p3p 4s4s 3d3d 4p4p 5s5s

Increasing Energy1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f 5g

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Designating Electron Configurations -

Standard DesignationStandard Designation

HH 1s1s11

HeHe 1s1s22

LiLi 1s1s22 2s 2s11

BeBe 1s1s22 2s 2s22

B 1s1s22 2s 2s2 2 2p2p11

C C 1s1s22 2s 2s2 2 2p2p22 Orbital Diagram DesignationOrbital Diagram Designation

H

He

1s

1sLi

Be

1s

1s 2s

2s

B

C1s

1s

2s

2s 2p

2p

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Core Designation - Core Designation - A designation of electronicconfiguration wherein the outer shell electronsare shown along with the “core” configuration of the closest previous noble gas.

Li

Na

K

Rb

Be

Mg

Ca

Sr

[He] 2s1

[Ne] 3s1

[Ar] 4s1

[Kr] 5s1

[He] 2s2

[Ne] 3s2

[Ar] 4s2

[Kr] 5s2

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Hund’s Rule of Maximum Multiplicity - Electronsoccupy a given subshell singly and with parallel spinsuntil each orbital in the subshell has one electron.

““Electrons try to stay as far apart as possible”Electrons try to stay as far apart as possible”

Elevator Analogy Bus Seat Analogy

B

C

N

[He] 2s2 2p1 [He]

[He] 2s2 2p2

[He] 2s2 2p3

[He]

[He]

2s 2p

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Assignment: Assignment: Write the electron configuration usingWrite the electron configuration usingall three types of designation for lead (Pb).all three types of designation for lead (Pb).

Electronic Configuration for postive ions (cations) -Cations are formed by removing electrons in orderof decreasing nn value. Electrons with the same nnvalue are removed in order of decreasing ll value.

Pb [Xe] 6sPb [Xe] 6s22 4f 4f1414 5d 5d1010 6p 6p22

Pb 1sPb 1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66 4s 4s22 3d 3d1010 4p 4p66 5s 5s22 4d 4d1010 5p 5p66 6s 6s22

4f4f1414 5d 5d1010 6p 6p22

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Assignment: Assignment: What are the electron configurations forWhat are the electron configurations for

FeFe2+2+ FeFe3+3+ CrCr CrCr3+3+ SeSe2- 2- ? ?

Questions?Questions?