Atomic Structure & Periodicity

Atomic Structure & Atomic Structure & PeriodicityPeriodicity

Chapter 7Chapter 7

Early 1900’sEarly 1900’s

Rutherford model Rutherford model detailed nucleus detailed nucleus plus electrons plus electrons moving around.moving around.

Did not explain Did not explain HOW electrons HOW electrons occupied that occupied that spacespace

Questions about ElectronsQuestions about Electrons

Chlorine, Argon, Potassium are found in Chlorine, Argon, Potassium are found in order on periodic tableorder on periodic table

Why do they react so differently?Why do they react so differently? Chlorine is yellow-green gas, poisonous, Chlorine is yellow-green gas, poisonous,

and reacts with many other elementsand reacts with many other elements Potassium is a highly reactive metal Potassium is a highly reactive metal

(solid)(solid) Argon is unreactive (inert) gasArgon is unreactive (inert) gas Why?Why?

Some AnswersSome Answers

Some answers were provided by the Some answers were provided by the light emitted by different elements light emitted by different elements when heated in a flame.when heated in a flame.

There is a relationship between There is a relationship between electrons and light emissions.electrons and light emissions.

Review – The Wave Nature Review – The Wave Nature of Lightof Light

Electromagnetic Radiation – a form of Electromagnetic Radiation – a form of energyenergy– Exhibits wave-like behavior as it travels Exhibits wave-like behavior as it travels

through spacethrough space Visible light is PART of the EM spectrumVisible light is PART of the EM spectrum

The EM Spectrum

Characteristics of EM Characteristics of EM RadiationRadiation

Wavelength – Wavelength – distance between distance between 2 waves2 waves

Frequency – waves Frequency – waves per second (herz)per second (herz)

Amplitude –Height Amplitude –Height of waveof wave

Speed – 3.0x10Speed – 3.0x1088 m/s in a vacuumm/s in a vacuum

(Rest)

Amplitude

EM Characteristics EM Characteristics RelationshipsRelationships

CC = = – C = speed of light (a constant)C = speed of light (a constant) (lambda) = wavelength in meters(lambda) = wavelength in meters = frequency in waves per second= frequency in waves per second

If wavelength goes up, frequency If wavelength goes up, frequency goes down.goes down.

If frequency goes up, wavelength If frequency goes up, wavelength goes downgoes down

Example ProblemExample Problem

A microwave of 3.44 x 10A microwave of 3.44 x 1099 Hz is used Hz is used to send information. What is the to send information. What is the wavelength?wavelength?– CC = =

C = 3.00 X 10C = 3.00 X 108 8 m/sm/s = 3.44 x 10= 3.44 x 1099 Hz (waves/sec) Hz (waves/sec) = ?? m= ?? m

= C/ = C/ = = 3.00 x 103.00 x 1088 m/s m/s = .872 x = .872 x 10-110-1 = .0872m= .0872m

3.44 x 103.44 x 1099 1/s 1/s

Planck’s ConstantPlanck’s Constant

Planck went further and quantified a Planck went further and quantified a ‘quanta’:‘quanta’:– E = E = hh

E = EnergyE = Energy h = Planck’s constant (6.626 x 10h = Planck’s constant (6.626 x 10-34-34 J) J) = frequency= frequency

Planck’s Theory: matter can absorb Planck’s Theory: matter can absorb or emit energy only in whole number or emit energy only in whole number multiples of multiples of hh, like 1 , like 1 hh, 2 , 2 hh, 3 , 3 hh, , etc.etc.

Photoelectric EffectPhotoelectric Effect

Planck’s Theory did not explain the Planck’s Theory did not explain the photoelectric effect:photoelectric effect:– When certain wavelengths of light shine on When certain wavelengths of light shine on

a metal, electrons (called photoelectrons) a metal, electrons (called photoelectrons) are emitted. How can this happen?are emitted. How can this happen? This is the principal used by photocells in your This is the principal used by photocells in your

calculatorscalculators

– This suggested that light was particles not This suggested that light was particles not waveswaves Something must be hitting the electrons for Something must be hitting the electrons for

them to bounce out….them to bounce out….

Einstein and the Dual Einstein and the Dual Nature of LightNature of Light

1905, Albert Einstein extended 1905, Albert Einstein extended Planck’s theory to include BOTH Planck’s theory to include BOTH wavelike and particle nature of lightwavelike and particle nature of light– A ‘photon’ a particle of light with no A ‘photon’ a particle of light with no

mass carries energymass carries energy– Energy of a photon depends on its Energy of a photon depends on its

frequencyfrequency EEphotonphoton = = hh

Atomic Emission SpectraAtomic Emission Spectra

The set of frequencies of EM radiation The set of frequencies of EM radiation emitted by atoms of the elementsemitted by atoms of the elements– Each element’s spectra is unique (one and only)Each element’s spectra is unique (one and only)

Because only certain colors of light are Because only certain colors of light are displayed, this means only certain displayed, this means only certain frequencies are emitted.frequencies are emitted.– This means that only photons with specific This means that only photons with specific

energies are emittedenergies are emitted Supports Planck’s Theory, but not classical Supports Planck’s Theory, but not classical

physics theory of that time.physics theory of that time.

Atomic Emission SpectraAtomic Emission Spectra

Quantum Theory and Quantum Theory and the Atomthe Atom

Section 2Section 2

Bohr Model of the AtomBohr Model of the Atom

Observed: hydrogen only emits Observed: hydrogen only emits certain frequencies of lightcertain frequencies of light

Niels Bohr (Danish) proposed a Niels Bohr (Danish) proposed a quantum model for the atom:quantum model for the atom:– Lowest energy level allowed for an Lowest energy level allowed for an

electron is its ‘ground state’electron is its ‘ground state’– When atom gains energy, electron goes When atom gains energy, electron goes

to a higher level, an ‘excited state’.to a higher level, an ‘excited state’.– The electron can have many ‘excited’ The electron can have many ‘excited’

statesstates

Bohr Model (Cont.)Bohr Model (Cont.)

– Each energy level corresponds to Each energy level corresponds to one quanta of energyone quanta of energy

Bohr model correctly predicted Bohr model correctly predicted the emission spectra for the emission spectra for hydrogen.hydrogen.

Bohr Atomic ModelBohr Atomic Model

Explaining the Hydrogen Explaining the Hydrogen Line SpectrumLine Spectrum

When energy is added, electron moves When energy is added, electron moves to a higher-energy orbit (fromto a higher-energy orbit (from n n = 1 to = 1 to nn = 2)= 2)

When atom moves back to lower-energy When atom moves back to lower-energy orbit, a ‘photon’ of energy is releasedorbit, a ‘photon’ of energy is released

Energy release is equal to the frequency Energy release is equal to the frequency of the light spectrum.of the light spectrum.

Because only certain atomic energies Because only certain atomic energies are possible (certain orbits), only are possible (certain orbits), only specific frequencies are emitted.specific frequencies are emitted.

Energy and AtomsEnergy and Atoms

Higher Energy Orbit Lower Energy Higher Energy Orbit Lower Energy OrbitOrbit– Specific distanceSpecific distance– Specific amount of energy (quanta)Specific amount of energy (quanta)– Specific frequencySpecific frequency– Specific frequency = specific colorSpecific frequency = specific color

Bohr Atomic ModelBohr Atomic Model

Bohr model failed to explain the Bohr model failed to explain the spectra of any other elementspectra of any other element

It was later determined that the Bohr It was later determined that the Bohr model was fundamentally correct.model was fundamentally correct.

Quantum Mechanical ModelQuantum Mechanical Model

1920’s – DeBroglie (French) 1920’s – DeBroglie (French) ExperimentsExperiments

Electron orbits behaved like waves, Electron orbits behaved like waves, could they have multiple frequencies?could they have multiple frequencies?

Could particles, including electrons, Could particles, including electrons, behave like waves?behave like waves?

If an electron has a wavelike motion If an electron has a wavelike motion AND is restricted to circular orbits of AND is restricted to circular orbits of fixed radius, the electron is allowed only fixed radius, the electron is allowed only certain wavelengthscertain wavelengths

Quantum Mechanical ModelQuantum Mechanical Model

DeBroglie EquationDeBroglie Equation = = h/mvh/mv

Predicts that ALL moving particles Predicts that ALL moving particles have wave characteristicshave wave characteristics– Auto moving at 25 m/s, with mass 910kg Auto moving at 25 m/s, with mass 910kg

has a wavelength of 2.9x10has a wavelength of 2.9x10-38-38 (way too (way too small to be detected)small to be detected)

– Electron at same speed has a Electron at same speed has a wavelength of 2.9x10wavelength of 2.9x10-5-5 (easily measured) (easily measured) About the same spacing as atoms in a crystalAbout the same spacing as atoms in a crystal

DeBroglie & HeisenbergDeBroglie & Heisenberg

Work on wave equations and electrons Work on wave equations and electrons resulted in:resulted in:– Electrons bound to the nucleus resemble a Electrons bound to the nucleus resemble a

standing wavestanding wave– Started working on the wave mechanical Started working on the wave mechanical

properties of the electrons.properties of the electrons.– Standing waves occur in musical instruments Standing waves occur in musical instruments

(strings are easiest to see/understand) where (strings are easiest to see/understand) where interference patterns are created by waves interference patterns are created by waves reflecting back from endsreflecting back from ends Standing waves only occur in whole number multiples Standing waves only occur in whole number multiples

of the original wave.of the original wave.

DeBroglie & HeisenbergDeBroglie & Heisenberg

If electrons behave like waves AND If electrons behave like waves AND can only exist in whole number can only exist in whole number multiples:multiples:– Electrons can have multiple frequencies Electrons can have multiple frequencies

in the same orbital, but only whole in the same orbital, but only whole number multiples of the ground state.number multiples of the ground state.

– Explains quantized energy.Explains quantized energy.

Multiples of WavelengthsMultiples of Wavelengths

Wavelengths in OrbitsWavelengths in Orbits

DeBroglie’s FindingsDeBroglie’s Findings Notice also that this Notice also that this

means the electron means the electron does not exist at does not exist at one single spot in one single spot in its orbit, it has a its orbit, it has a wave nature and wave nature and exists at all places exists at all places in the allowed orbit. in the allowed orbit. And the Bohr atom And the Bohr atom really looks like the really looks like the following diagram: following diagram:

SchrSchröödinger Wave Equationdinger Wave Equation

1926 Erwin Schr1926 Erwin Schröödinger (Austria) dinger (Austria) furthered the theory.furthered the theory.– Created an equation that treated the Created an equation that treated the

hydrogen atom’s electron like a wavehydrogen atom’s electron like a wave– New model applied equally well to other New model applied equally well to other

atomsatoms This body of knowledge became the This body of knowledge became the

“quantum mechanical model of the “quantum mechanical model of the atom”atom”

Schrodinger EquationSchrodinger Equation

H H ΨΨ = E = E ΨΨ– H = mathematical ‘operator’ H = mathematical ‘operator’ – ΨΨ = coordinates of electron’s position in = coordinates of electron’s position in

3-D space3-D space– E = total energy of the electronE = total energy of the electron– Equation results in many solutionsEquation results in many solutions– So So ΨΨ really represents an electron really represents an electron

orbitalorbital

Just For Reference…Just For Reference…The Schrödinger equation is the fundamental equation of physics for describing quantum mechanical behavior. It is also often called the Schrödinger wave equation, and is a partial differential equation that describes how the wavefunction of a physical system evolves over time. Viewing quantum mechanical systems as solutions to the Schrödinger equation is sometimes known as the Schrödinger picture, as distinguished from the matrix mechanical viewpoint, sometimes known as the Heisenberg picture. The time-dependent one-dimensional Schrödinger equation is given by

where i is the imaginary unit, is the time-dependent wavefunction, is h-bar, V(x) is the potential, and

is the Hamiltonian operator. However, the equation can be separated into temporal and spatial parts using separation of variables to write

(2)

thus obtaining

(3)

Setting each part equal to a constant then gives

(6)

And so on and so on…..

More Evidence of WavesMore Evidence of Waves Diffraction patterns (rainbows) occur Diffraction patterns (rainbows) occur

when light hits a regular array of when light hits a regular array of points or linespoints or lines– CD/DVD grooves result in prism effect.’CD/DVD grooves result in prism effect.’

Xrays through a sodium chloride Xrays through a sodium chloride crystal produce a diffraction pattern.crystal produce a diffraction pattern.– Can only happen with waves providing Can only happen with waves providing

an interference pattern of high and low an interference pattern of high and low troughstroughs

What does this mean about What does this mean about electron orbits?electron orbits?

Atomic orbitals are NOT Bohr Atomic orbitals are NOT Bohr orbitals!orbitals!

Atomic orbits are 3-dimensional Atomic orbits are 3-dimensional regions around the nucleus (like a regions around the nucleus (like a fuzzy cloud).fuzzy cloud).

Where exactly is the electron?Where exactly is the electron?– We don’t know!We don’t know!

Heisenberg Uncertainty Heisenberg Uncertainty PrinciplePrinciple

It is impossible to make any measurement It is impossible to make any measurement on an object without disturbing the object on an object without disturbing the object at least a little;at least a little;

States:States:– That is is fundamentally impossible to know That is is fundamentally impossible to know

precisely both the velocity and the position of a precisely both the velocity and the position of a particle at the same time.particle at the same time.

Mathematically:Mathematically:

x mv4

h

ΔX = particle position uncertainty

Δ(mv) = momentum uncertaintyH = Plank’s constant

Heisenberg Uncertainty Heisenberg Uncertainty PrinciplePrinciple Minimum uncertainty is 4Minimum uncertainty is 4ΨΨ

More accurately we know particle’s More accurately we know particle’s position, less accuracy is known about position, less accuracy is known about momentum.momentum.

More accurately we know particle More accurately we know particle momentum, less momentum, less accuratelyaccurately we know we know particle positionparticle position

x mv4

h

Heisenberg Uncertainty Heisenberg Uncertainty PrinciplePrinciple

What Does This Mean?What Does This Mean? The squared wave function provides a The squared wave function provides a

‘relative probability’ of finding an electron at ‘relative probability’ of finding an electron at a particular position. Therefore, if Na particular position. Therefore, if N11 is is position 1 and Nposition 1 and N22 is position 2, the relative is position 2, the relative probabilities of finding an electron at a probabilities of finding an electron at a particular position is Nparticular position is N11/N/N22

This gives us an electron density (or This gives us an electron density (or electron probability) map Which shows us electron probability) map Which shows us an electron ‘cloud’ of probabilities.an electron ‘cloud’ of probabilities.

Also gives us a probability of finding an Also gives us a probability of finding an electron a certain distance from the nucleuselectron a certain distance from the nucleus

Electron Probability GraphsElectron Probability Graphs

What Does This Mean about What Does This Mean about Electron OrbitalsElectron Orbitals

If you use Schrodinger equation for hydrogen, you If you use Schrodinger equation for hydrogen, you find many wave functions (orbitals) that satisfy it.find many wave functions (orbitals) that satisfy it.– Each orbital is characterized by a series of numbers Each orbital is characterized by a series of numbers

called called QUANTUM NUMBERSQUANTUM NUMBERS..– Quantum numbers describe properties of the orbitals.Quantum numbers describe properties of the orbitals.

Principal quantum numbers are assigned to Principal quantum numbers are assigned to indicate relative size and energy of orbitalsindicate relative size and energy of orbitals– (n) – (n) – principal quantum number – has integer values 1, principal quantum number – has integer values 1,

2, 3,…2, 3,…– As As nn increases, orbital gets larger, has more energy, is increases, orbital gets larger, has more energy, is

less tightly bound to nucleus, energy is less negative;less tightly bound to nucleus, energy is less negative;– Up to 7 energy levels have been detected for hydrogenUp to 7 energy levels have been detected for hydrogen– As (n) increases, orbital is larger and electron spends As (n) increases, orbital is larger and electron spends

more time further from nucleusmore time further from nucleus


Angular Momentum number Angular Momentum number ((ll)) has has integer values from 0 to n-1 for each value integer values from 0 to n-1 for each value of of nn– This quantum number is related to the This quantum number is related to the

shapeshape of the orbital of the orbital ll = 0 is = 0 is ss ll = 1 is = 1 is pp ll = 2 is = 2 is dd ll = 3 is = 3 is ff


Each principal energy level can have Each principal energy level can have sublevelssublevels– Principal energy level one has only one Principal energy level one has only one

sublevelsublevel– Principal energy level 2 has 2 sublevelsPrincipal energy level 2 has 2 sublevels– Principal energy level 3 has 3 sublevelsPrincipal energy level 3 has 3 sublevels– And so on..And so on..


Sublevels are labeled Sublevels are labeled ss, , pp, , dd, or , or ff according to their shapeaccording to their shape– ss sublevels are spherical sublevels are spherical– pp sublevels are dumbell shaped sublevels are dumbell shaped– dd sublevels and sublevels and ff sublevels are not all sublevels are not all

shaped the same.shaped the same. Each orbital can have at most 2 Each orbital can have at most 2

electronselectrons


Principal level one has only ONE Principal level one has only ONE sublevelsublevel– Designated as 1s (spherical)Designated as 1s (spherical)– 2 total electrons (2 elements in 12 total electrons (2 elements in 1stst row) row)

Principal level 2 has 2 sublevelsPrincipal level 2 has 2 sublevels– Designated as 2s and 2pDesignated as 2s and 2p– 2s is spherical (like 1s) but larger2s is spherical (like 1s) but larger– 2p has three dumbbell shaped orbitals on 2p has three dumbbell shaped orbitals on

each of three axiseach of three axis– Total 8 electrons (8 elements)Total 8 electrons (8 elements)


Magnetic Quantum Number Magnetic Quantum Number ((mmll)) : : – Related to orientation of orbital in space Related to orientation of orbital in space

relative to other orbitals of the atomrelative to other orbitals of the atom– Has integer values between Has integer values between ll and and –l–l, including , including

zero.zero. Quiz: For Principal quantum level n=5, list Quiz: For Principal quantum level n=5, list

all allowed subshells and give designation all allowed subshells and give designation of each:of each:– ll=0=0 ll=1=1 ll=2 =2 ll=3=3 ll=4=4– 5s5s 5p5p 5d5d 5d5d 5f5f


Review: an orbital can best be represented Review: an orbital can best be represented by a probability distribution, or by an area by a probability distribution, or by an area that surrounds 90% of the probability areasthat surrounds 90% of the probability areas– Areas between areas of high probability have Areas between areas of high probability have

probability of zeroprobability of zero– These are called nodal surfaces, or nodesThese are called nodal surfaces, or nodes– Nodes increase as Nodes increase as nn increases increases– For For ss orbitals, these resemble spherical shapes orbitals, these resemble spherical shapes– For For pp orbitals have ‘lobes’ labeled along the xyz orbitals have ‘lobes’ labeled along the xyz

axes.axes.– Very complex orbital probability distributionVery complex orbital probability distribution


Note p orbital alignment along the xyz axes


Note: d orbitals are BETWEEN the xyz axes.


Energy of a particular Electron orbital Energy of a particular Electron orbital is determined only by its value of is determined only by its value of nn..– All orbitals with same value of All orbitals with same value of nn have have

the same energy (said to be the same energy (said to be degeneratedegenerate))

Electron Spin and Pauli Electron Spin and Pauli PrinciplePrinciple

First postulated by Goudsmit and Uhlenbeck at First postulated by Goudsmit and Uhlenbeck at University of Leyden (Netherlands)University of Leyden (Netherlands)– A fourth quantum number was necessary to account for A fourth quantum number was necessary to account for

details in the emission spectrum of atomsdetails in the emission spectrum of atoms– Spectral data indicates a magnetic moment with two Spectral data indicates a magnetic moment with two

possible orientations.possible orientations.– Assumed an electron could have 2 possible spin statesAssumed an electron could have 2 possible spin states– Lead to Lead to electron spin quantum numberelectron spin quantum number ( (mmss))– Electron spin can only have 2 values: +½ and –½ Electron spin can only have 2 values: +½ and –½ – Significance given by Pauli exclusion principle: Significance given by Pauli exclusion principle: in a in a

given atom, no two electrons can have the same 4 given atom, no two electrons can have the same 4 quantum numbers (n, l, mquantum numbers (n, l, mll and m and mss

– Since an orbital can only have 2 electrons, they must Since an orbital can only have 2 electrons, they must have opposite spinshave opposite spins

ReviewReview

Each principal energy level can have Each principal energy level can have the same number of sublevels as the the same number of sublevels as the level numberlevel number

Each sublevel orbital has a different Each sublevel orbital has a different shapeshape

Each orbital can have only 2 Each orbital can have only 2 electronselectrons

What does this mean?What does this mean?

Electron Arraignment Electron Arraignment follows Rulesfollows Rules

Low energy level systems are more stable Low energy level systems are more stable than high-energy systemsthan high-energy systems– Atoms will assume the electron arrangement Atoms will assume the electron arrangement

that gives the atom the lowest energythat gives the atom the lowest energy– Most stable is the “ground state” (lowest energy)Most stable is the “ground state” (lowest energy)

Three rules/principles for arranging Three rules/principles for arranging electronselectrons– AufbauAufbau– Pauli Exclusion principlePauli Exclusion principle– Hund’s RuleHund’s Rule

Aufbau PrincipleAufbau Principle

Each electron occupies the lowest Each electron occupies the lowest energy level availableenergy level available– Learn the sequence of atomic orbitals Learn the sequence of atomic orbitals

from lowest to highest:from lowest to highest:

Aufbau DiagramAufbau Diagram

#4 – also do electron DOT diagram, #7 & 8 – SHOW YOUR WORK

Using AufbauUsing Aufbau All orbitals related to the same energy level are of All orbitals related to the same energy level are of

equal energyequal energy– All 2p orbitals have the same energyAll 2p orbitals have the same energy

In a multi-electron atom, the energy sublevels In a multi-electron atom, the energy sublevels within a principal energy level have different within a principal energy level have different energies:energies:– 2p orbitals are higher energy than 2s orbitals2p orbitals are higher energy than 2s orbitals

The sequence of sublevels within a principle level The sequence of sublevels within a principle level in increasing energy is: s, p, d, and fin increasing energy is: s, p, d, and f

Orbitals related to energy sublevels within one Orbitals related to energy sublevels within one principle energy level can overlap orbitals related principle energy level can overlap orbitals related to another principal levelto another principal level– Notice: 4s is lower than 3dNotice: 4s is lower than 3d

Hund’s RuleHund’s Rule

Because negatively charged electrons Because negatively charged electrons repel each other, they try to get as far repel each other, they try to get as far away from each other as possible, away from each other as possible, therefore:therefore:

Single electrons with the same spin Single electrons with the same spin will occupy each equal energy orbital will occupy each equal energy orbital before before additional electrons with additional electrons with opposite spins occupy the same opposite spins occupy the same orbitals.orbitals.

WHAT? WHAT?

Hund’s RuleHund’s Rule

123

4

Polyelectronic AtomsPolyelectronic Atoms

Quantum model works for hydrogen. How Quantum model works for hydrogen. How about all other atoms as well?about all other atoms as well?– Polyelectronic = atoms with multiple electronsPolyelectronic = atoms with multiple electrons

Quantum model must account for 3 types of Quantum model must account for 3 types of energy:energy:– Kinetic energy of electrons as the move around Kinetic energy of electrons as the move around

nucleusnucleus– Potential energy of attraction between nucleus Potential energy of attraction between nucleus

and electronsand electrons– Potential energy of repulsion between two Potential energy of repulsion between two

electronselectrons


Schrodinger equation cannot be solved Schrodinger equation cannot be solved exactly for helium atomexactly for helium atom– How to deal with repulsion between electronsHow to deal with repulsion between electrons

Electron pathways are unknownElectron pathways are unknown Electron repulsions cannot be calculated exactlyElectron repulsions cannot be calculated exactly

– Called Called electron correlation prblem.electron correlation prblem. Using approximations, we can treat the Using approximations, we can treat the

electrons as if they were moving in an electrons as if they were moving in an electronic field that is the net result of the electronic field that is the net result of the nuclear attraction and the average nuclear attraction and the average repulsions of all other electronsrepulsions of all other electrons


Using Sodium, Single out Outermost Using Sodium, Single out Outermost Electron only:Electron only:– Clearly attracted to positive nucleusClearly attracted to positive nucleus– Also feels repulsions by other 10 electronsAlso feels repulsions by other 10 electrons– Net effect is electron is not bound as Net effect is electron is not bound as

tightly to nucleus as if there were no other tightly to nucleus as if there were no other electronselectrons

– Electron is said to be Electron is said to be screenedscreened or or shieldedshielded by repulsions of other electronsby repulsions of other electrons

– Leads to pictures of hydrogen-like orbitals Leads to pictures of hydrogen-like orbitals or these atomsor these atoms


For hydrogen atoms, all orbitals for same For hydrogen atoms, all orbitals for same principal energy level are the same principal energy level are the same ((degeneratedegenerate). ). – Not the case for polyelectronic atomsNot the case for polyelectronic atoms– For a principal quantum level, polyelectronic For a principal quantum level, polyelectronic

atoms have orbital energies of:atoms have orbital energies of: EEnsns<E<Enpnp<E<Endnd<E<Enfnf

– In other words, they ‘prefer’ orbitals in order s, In other words, they ‘prefer’ orbitals in order s, p, d, f, because energy is lower.p, d, f, because energy is lower.

– A 2s electron ‘penetrates’ to the nucleus more A 2s electron ‘penetrates’ to the nucleus more than the 2p orbital electrons.than the 2p orbital electrons.

Periodic TablePeriodic Table

Know how to use the Periodic Table Know how to use the Periodic Table to configure electrons for any to configure electrons for any element.element.

Trends in Periodic TableTrends in Periodic Table

What is Ionization Energy?What is Ionization Energy?– Energy required to remove an electron from a Energy required to remove an electron from a

gaseous atomgaseous atom– First ionization energy takes first electronFirst ionization energy takes first electron– Second ionization energy – energy required to Second ionization energy – energy required to

remove the second electronremove the second electron What is the trend in ionization energy on the What is the trend in ionization energy on the

Periodic Table?Periodic Table?– First ionization energy increases from left to rightFirst ionization energy increases from left to right– First ionization energy decreases from top to First ionization energy decreases from top to

bottom.bottom.

Trends in Electron AffinityTrends in Electron Affinity

What is Electron Affinity?What is Electron Affinity?– Energy change associated with the Energy change associated with the

addition of an electron to a gaseous addition of an electron to a gaseous atomatom Related to electronegativityRelated to electronegativity If addition of electron is exothermic, electron If addition of electron is exothermic, electron

affinity will be negative (like enthalpy)affinity will be negative (like enthalpy)

Trends ElectronegativityTrends Electronegativity

Electron Affinity TrendsElectron Affinity Trends

Atomic Radius TrendsAtomic Radius Trends Atomic radius often called Atomic radius often called covalent radiicovalent radii

because they must be measured from like because they must be measured from like atoms.atoms.– Cannot be measured directlyCannot be measured directly– Measured as ½ distance between nucleiMeasured as ½ distance between nuclei– If diatomic molecules do not exist, it is measured If diatomic molecules do not exist, it is measured

from covalent compounds where radii are from covalent compounds where radii are measureable.measureable.

General Trends:General Trends:– Radii increase with principal quantum number. Radii increase with principal quantum number.

Why?Why?– Radii decrease from left to right. Why?Radii decrease from left to right. Why?

Explain in terms of shieldingExplain in terms of shielding

Properties of Alkali MetalsProperties of Alkali Metals

Properties all based on same valence electronsProperties all based on same valence electrons– Chemically very reactive metalsChemically very reactive metals– Overall density increases going downOverall density increases going down– Melting point and boiling point decrease going down Melting point and boiling point decrease going down

is not typicalis not typical– Chemical property: ability to lose valence electronChemical property: ability to lose valence electron

Low first ionization energyLow first ionization energy React with nonmetals to form solidsReact with nonmetals to form solids Acts as reducing agentActs as reducing agent Reducing power increases based on first ionization energyReducing power increases based on first ionization energy

Increases with period.Increases with period.

Atomic Structure & Periodicity

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