why is the sky blue?

•Why is the sky blue?Why is the sky blue?

Chemistry Chapter 11Chemistry Chapter 11Arrangement of Electrons in Arrangement of Electrons in

AtomsAtoms

The 1998 Nobel Prize in Physics was awarded "for the discovery of a new form of quantum fluid with fractionally charged excitations." At the left is a computer graphic of this kind of state.

The Puzzle of the AtomThe Puzzle of the Atom Protons and electrons are attracted to each

other because of opposite charges

Electrically charged particles moving in a curved path give off energy

Despite these facts, atoms don’t collapse (Rutherford’s Model did not explain why! We need a new model!)

Light is made up of fluctuating electric and magnetic fields that do not require the existence of matter.

Visible light is a kind of electromagnetic radiation (form of E with wavelike behavior as travels through space.)

All form of light travel at a speed of 3.0 x 108 m/s

What is light?What is light?

Wave-Particle DualityWave-Particle DualityJJ Thomson won the Nobel prize for describing the electron as a particle.

His son, George Thomson won the Nobel prize for describing the wave-like nature of the electron.

The electron

is a particle!

The electron is an energy

wave!

Confused??? You’ve Got Confused??? You’ve Got Company!Company!

“No familiar conceptions can be woven around the

electron; something unknown is doing we

don’t know what.”

Physicist Sir Arthur Eddington

The Nature of the Physical World

1934

c = C = speed of light, a constant (3.00 x 108 m/s)

= frequency, in units of hertz (hz, sec-1)

= wavelength, in meters

Electromagnetic radiation Electromagnetic radiation propagates through space as a wave propagates through space as a wave moving at the speed of light. moving at the speed of light. (ALL (ALL FORMS!)FORMS!)

…produces all of the colors in a continuous spectrum

Spectroscopic analysis of the visible Spectroscopic analysis of the visible spectrum…spectrum…

Types of electromagnetic radiation:Types of electromagnetic radiation:

Light as Light as ParticlesParticles

• 1900’s German physisist Max Planck studied 1900’s German physisist Max Planck studied emission of light by hot objects.emission of light by hot objects.

• Suggested objects emitted in small specific Suggested objects emitted in small specific amounts called amounts called quantaquanta..

• QuantumQuantum: the minimum quantity of E that can : the minimum quantity of E that can be lost or gained by an atom. be lost or gained by an atom.

• Proposed E = hvProposed E = hv– h is “Planck’s Constant” 6.626 x 10h is “Planck’s Constant” 6.626 x 10-34-34 Js Js

E = hEE = Energy, in units of Joules (kg·m= Energy, in units of Joules (kg·m22/s/s22))

hh = Planck’s constant (6.626 x 10= Planck’s constant (6.626 x 10-34-34 J·s) J·s)

= frequency, in units of hertz (hz, sec= frequency, in units of hertz (hz, sec-1-1))

The energy (The energy (E E ) of electromagnetic ) of electromagnetic radiation is directly proportional to radiation is directly proportional to the frequency (the frequency () of the radiation.) of the radiation.

Photoelectric Effect (early Photoelectric Effect (early 1900’s)1900’s)

• Could Could NOTNOT be explained by the wave be explained by the wave theory of light.theory of light.

• Refers to the emission of e’ from a Refers to the emission of e’ from a metal when light shines on it.metal when light shines on it.– For a given metal, no e’ were emitted For a given metal, no e’ were emitted

if the light was below a certain if the light was below a certain vv– Wave theory said any Wave theory said any vv could supply could supply

enough E to eject any e’enough E to eject any e’

What are wave-like and particle What are wave-like and particle like properties???like properties???

Wave PropertiesWave Properties Particle PropertiesParticle Properties

Measurable frequency Measurable frequency and wavelengthand wavelength

Absorbed and emitted Absorbed and emitted by matter by matter (photoelectric effect)(photoelectric effect)

Ability to interfere and Ability to interfere and diffractdiffract

Emission of light by hot Emission of light by hot objectsobjects

Significant feature is Significant feature is repetitive naturerepetitive nature

Creation of line-Creation of line-emission spectra of emission spectra of elementselements

Albert Einstein (1905)Albert Einstein (1905)

• Suggested dual wave-particle natureSuggested dual wave-particle nature• Each particle carried a Each particle carried a quantum quantum of E.of E.

– Einstein called these particles “Einstein called these particles “photonsphotons””– E photon = hE photon = hvv

• For each e’ to be removed, must be struck by For each e’ to be removed, must be struck by single photon with minimum E required to single photon with minimum E required to knock e’ loose.knock e’ loose.

• e’ of e’ of differentdifferent metals require metals require differentdifferent minimum v to exhibit photoelectric effect.minimum v to exhibit photoelectric effect.

Hydrogen-Atom Line Emission Hydrogen-Atom Line Emission SpectrumSpectrum

• When current is passed through a gas at low P, When current is passed through a gas at low P, the potential E of some of the gas atoms the potential E of some of the gas atoms increases.increases.– Ground stateGround state: lowest E state of an atom: lowest E state of an atom– Excited stateExcited state: atom has higher potential E : atom has higher potential E

than the ground state.than the ground state.• When at atom returns to ground state, it gives When at atom returns to ground state, it gives

off E. (off E. (neonneon lights) lights)• Results in Hydrogen’s Line Emission Spectrum. Results in Hydrogen’s Line Emission Spectrum.

…produces a “bright line” spectrum

Spectroscopic analysis of the Spectroscopic analysis of the hydrogen spectrum…hydrogen spectrum…

This produces bandsof light with definitewavelengths.

Electron Electron transitionstransitionsinvolve jumps of involve jumps of definite amounts definite amounts ofofenergy.energy.

The Bohr Model of the AtomThe Bohr Model of the Atom

Neils Bohr

I pictured electrons orbiting the nucleus much like planets orbiting the sun.But I was wrong! They’re more like bees around a hive.

WRONG!!!

What does a line emission What does a line emission spectrum tell you?spectrum tell you?

• Proves that e’ are Proves that e’ are constantly movingconstantly moving from one from one E level to another.E level to another.

• Proves that the distance between the two Proves that the distance between the two levels is always the same.levels is always the same.

• UseUse– Identification of unknown samplesIdentification of unknown samples

Bohr’s Bohr’s Model of H AtomModel of H Atom

• Linked an atom’s Linked an atom’s e’e’ to to photon emissionphoton emission• Said that e’ can circle the nucleus only Said that e’ can circle the nucleus only

is specific paths or is specific paths or orbitsorbits..• Orbits are separated from the nucleus Orbits are separated from the nucleus

by large empty spaces (by large empty spaces (nodesnodes) where ) where the e- cannot exist. (Rungs on a ladder)the e- cannot exist. (Rungs on a ladder)

• Remember, Remember, E increases as e’ are furtherE increases as e’ are further from the nucleusfrom the nucleus. .

Bohr’s Bohr’s Model of H AtomModel of H Atom

• While an e’ is in orbit, it While an e’ is in orbit, it cannot cannot gain nor gain nor lose Elose E

• It It cancan, move to a higher E level , move to a higher E level IFIF it it gains the amount of E = to the gains the amount of E = to the difference between the higher E orbit difference between the higher E orbit and the lower energy orbit.and the lower energy orbit.

• When falls, it emits a When falls, it emits a PHOTON PHOTON = to the = to the difference.difference.

• AbsorptionAbsorption gains E/ gains E/EmissionEmission gives off E gives off E

Take the good with the bad Take the good with the bad (Bohr’s Model)(Bohr’s Model)

• Good:Good:– Led scientists to believe a similar model Led scientists to believe a similar model

could be applied to all atoms.could be applied to all atoms.

• Bad:Bad:– Yikes!!! Did not explain the spectra of Yikes!!! Did not explain the spectra of

atoms with more than one e’ or chemical atoms with more than one e’ or chemical behavior of atoms!behavior of atoms!

The Wave-like ElectronThe Wave-like Electron

Louis deBroglie

The electron propagates through space as an energy

wave. To understand the atom, one must

understand the behavior of

electromagnetic waves.

Schrodinger Wave EquationSchrodinger Wave Equation

22

2 2

8dh EV

m dx

Equation for probabilityprobability of a single electron being found along a single axis (x-axis)Erwin Schrodinger

Standing waves do not propagate through space Standing waves are fixed at both ends

The electron as a standing The electron as a standing wave:wave:

Orbital shapes are defined as the surface that contains 90% of the total electron probability.

An orbital is a region within an atom where thereAn orbital is a region within an atom where thereis a probability of finding an electron. This is a is a probability of finding an electron. This is a probability diagram for the s orbital in the probability diagram for the s orbital in the first first energy level…energy level…

Heisenberg Uncertainty Heisenberg Uncertainty PrinciplePrinciple

.

…

“One cannot simultaneously determine both the position and momentum of an electron.”

WernerHeisenberg

Orbitals of the same shape (s, for instance) grow larger as n increases…

Nodes are regions of low probability within an orbital.

Sizes of Sizes of ss orbitals orbitals

The s orbital has a spherical shape centered aroundthe origin of the three axes in space.

s orbital shape

There are three dumbbell-shaped p orbitals in each energy level above n = 1, each assigned to its own axis (x, y and z) in space.

PP orbital shape orbital shape

Things get a bit more complicated with the five d orbitals that are found in the d sublevels beginning with n = 3. To remember the shapes, think of “double dumbells”

…and a “dumbell with a donut”!

d orbital shapes

Shape of f orbitalsShape of f orbitals

Orbital filling tableOrbital filling table

Electron configuration of the Electron configuration of the elements of the first three elements of the first three

seriesseries

Irregular confirmations of Cr and CuIrregular confirmations of Cr and Cu

Chromium steals a 4s electron to halffill its 3d sublevel

Copper steals a 4s electron to FILL its 3d sublevel

Pauli Exclusion PrinciplePauli Exclusion Principle

No two electrons in an atom can have the same four quantum numbers.

Wolfgang Pauli

Quantum NumbersQuantum Numbers

Each electron in an atom has a unique set of 4 quantum numbers which describe it.

Principal quantum number Angular momentum quantum number Magnetic quantum number Spin quantum number

Principal Quantum NumberPrincipal Quantum NumberGenerally symbolized by n, it denotes the shell (energy level) in which the electron is located.

Number of electrons that can fit in a shell:

2n2

Angular Momentum Angular Momentum Quantum NumberQuantum Number

The angular momentum quantum number,

generally symbolized by l, denotes the orbital (subshell) in which the electron is located.

Magnetic Quantum NumberMagnetic Quantum NumberThe magnetic quantum number, generally symbolized by m, denotes the orientation of the electron’s orbital with respect to the three axes in space.

Spin Quantum NumberSpin Quantum NumberSpin quantum number denotes the behavior (direction of spin) of an electron within a magnetic field.

Possibilities for electron spin:

1

2

1

2

Assigning the NumbersAssigning the Numbers1. Principle: n = shell (period)2. Angular Momentum: l = shape (s=0,

p=1, d=2)3. Magnetic: ml = +l to -l4. Spin: +1/2 or – 1/2

ChlorineChlorine

• Write the orbital notationWrite the orbital notation• Write the electron configurationWrite the electron configuration

• So, can we now write the quantum #’s for So, can we now write the quantum #’s for each e’?each e’?

Electron Conf. and Quant #’sElectron Conf. and Quant #’se’e’ nn

principleprinciplell

shapeshapeMMll

orientaorientationtion

spinspin e’ e’ config.config.

1,21,2 11 00 00 +/- 1/2+/- 1/2

- - 1s1s22

3,43,4 22 00 00 +/- 1/2+/- 1/2

2s2s22

5-105-10 22

22

22

11

11

11

-1-1

00

+1+1

+/- 1/2+/- 1/2 2p2p66

11,1211,12 33 00 00 +/- 1/2+/- 1/2 3s3s22

13-1713-17 33

33

33

11

11

11

-1-1

00

+1+1

+/- 1/2+/- 1/2 3p3p55

KeyKey Terms Terms

• Ground StateGround State Electron Configurations Electron Configurations (1s(1s222s2s22…/…/Orbital NotationsOrbital Notations __ __ __ __ __ __ __ __ __ __

• Aufbau PrincipleAufbau Principle (lowest first/periodic guide) (lowest first/periodic guide)• Hund’s RuleHund’s Rule: Single e’ before pairing begins: Single e’ before pairing begins• Pauli ExclusionPauli Exclusion (up/down—no 2 e’ same set of (up/down—no 2 e’ same set of

quant. #’s)quant. #’s)• Highest Occupied LevelHighest Occupied Level• Inner-Shell e’Inner-Shell e’• Noble Gas NotationNoble Gas Notation

Orbitals in outer energy levels DO penetrate intolower energy levels.

This is a probabilityDistribution for a 3s orbital.

What parts of thediagram correspondto “nodes” – regionsof zero probability?

Penetration #1

Which of the orbital types in the 3rd energy levelDoes not seem to have a “node”?

WHY NOT?

Penetration #2

Principle, angular momentum, and magnetic quantum Principle, angular momentum, and magnetic quantum numbers: numbers: nn, , ll, and , and mmll

Chemistry Chapter 5Chemistry Chapter 5

The Periodic LawThe Periodic Law

– Properties of the elements recur in Properties of the elements recur in regular cycles (regular cycles (periodicallyperiodically) when the ) when the elements are arranged in order of elements are arranged in order of increasing increasing atomic massatomic mass..

Law of Mendeleev:Law of Mendeleev:

Mendeleev’s Periodic TableMendeleev’s Periodic Table

Dmitri Mendeleev

Missing?Missing?

1414

SiSi

28.0928.09

????

5050

SnSn

118.71118.71

Named missing element “Ekasilicon”

From base word “eka” meanging next in order

““Ekasilicon”Ekasilicon”

Predicted Predicted PropertiesProperties

Observed Observed PropertiesProperties

Atomic MassAtomic Mass 72 amu72 amu

Density Density 5.5 g/cm5.5 g/cm33

Melting PointMelting Point 825° C825° C

““Ekasilicon”Ekasilicon”

Predicted Predicted PropertiesProperties

Observed Observed PropertiesProperties

Atomic MassAtomic Mass 72 amu72 amu 72.61 amu72.61 amu

Density Density 5.5 g/cm5.5 g/cm33 5.32 g/cm5.32 g/cm33

Melting PointMelting Point 825° C825° C 938° C938° C

““Ekasilicon”Ekasilicon”

Predicted Predicted PropertiesProperties

Observed Observed PropertiesProperties

Oxide FormulaOxide Formula XOXO22 GeOGeO22

Chloride FormulaChloride Formula XClXCl44 GeClGeCl44

Modern Russian TableModern Russian Table

Orbital filling tableOrbital filling table

Periodic Table with Group NamesPeriodic Table with Group Names

• Called Called main groupmain group elements elements– 1: ns1: ns11 Alkali Metals Alkali Metals– 2: ns2: ns22 Alkaline Earth Metals Alkaline Earth Metals

s-block elements:s-block elements:

• Called Called main groupmain group elements elements– 13: ns13: ns22npnp11 Boron Family Boron Family– 14: ns14: ns22npnp22 Carbon Family Carbon Family– 15: ns15: ns22npnp33 Nitrogen Family Nitrogen Family– 16: ns16: ns22npnp44 Oxygen Family Oxygen Family– 17: ns17: ns22npnp55 Fluorine Family(Halogens) Fluorine Family(Halogens)– 18: ns18: ns22npnp66 Noble Gases Noble Gases

p-block elements:p-block elements:

• Mostly brittle solidsMostly brittle solids• Harder and denser than s-block Harder and denser than s-block • Softer and less dense than d-blockSofter and less dense than d-block• With exception of Bismuth, found in nature With exception of Bismuth, found in nature

only as compoundonly as compound• Once obtained as free metals, that are stable Once obtained as free metals, that are stable

in the presence of airin the presence of air

Metalloids:Metalloids:

• Called Called transition metalstransition metals– metals with typical metallic propertiesmetals with typical metallic properties– Less reactiveLess reactive than group 1 or 2 than group 1 or 2– Some are so unreactive that they do Some are so unreactive that they do

not easily form compounds (e.g. not easily form compounds (e.g. palladium, platinum, and gold)palladium, platinum, and gold)

d-block elements:d-block elements:

• Between Group 3 & 4 Between Group 3 & 4 • Shiny metalsShiny metals• Similar in reactivity to Group 2Similar in reactivity to Group 2

– Lanthanides (period 6): Lanthanides (period 6): • rare earth metalsrare earth metals

– Actinides (period 7):Actinides (period 7):• All radioactiveAll radioactive• First 4 have been found naturally, rest First 4 have been found naturally, rest

are lab madeare lab made

f block elements:f block elements:

Half of the distance between nuclei in covalently bonded diatomic molecule "covalent atomic radii"

Periodic Trends in Atomic Radius

Radius decreases across a period Increased effective nuclear charge dueto decreased shielding

Radius increases down a group Addition of principal quantum levels

Determination of Atomic Radius:Determination of Atomic Radius:

Table of Table of Atomic Atomic

RadiiRadii

Increases for successive electrons taken from the same atom

Tends to increase across a period

Electrons in the same quantum level do not shield as effectively as electrons in inner levels

    Tends to decrease down a group

Outer electrons are further from thenucleus

Ionization EnergyIonization Energy - the energy required to - the energy required to removeremove an an electron from an atom electron from an atom

Ionization of MagnesiumIonization of Magnesium Mg + 738 kJ Mg+ + e-

Mg+ + 1451 kJ Mg2+ + e-

Mg2+ + 7733 kJ Mg3+ + e-

Table of 1Table of 1stst Ionization Energies Ionization Energies

Another Way to Look at Ionization EnergyAnother Way to Look at Ionization Energy

Affinity tends to increase across a period

Affinity tends to decrease as you go down in a group

Electrons further from the nucleusexperience less nuclear attraction

Some irregularities due to repulsive forces in the relatively small p orbitals

Electron AffinityElectron Affinity - the energy change associated - the energy change associated with the with the additionaddition of an electron of an electron

Table of Electron AffinitiesTable of Electron Affinities

Ionic RadiiIonic Radii

Cations Positively charged ions

Smaller than the corresponding atomAnions

Negatively charged ions Larger than the corresponding atom

Table of Ion SizesTable of Ion Sizes

• The electrons available to be lost, gained, or The electrons available to be lost, gained, or shared in the formation of chemical shared in the formation of chemical compounds.compounds.

• Valence Electrons hold atoms together in Valence Electrons hold atoms together in chemical compounds.chemical compounds.

Valence Electrons Valence Electrons oror

“Outer Shell Electrons” “Outer Shell Electrons”

Electronegativity Electronegativity

A measure of the ability of an atom in a chemicalcompound to attract electrons. (same trends as electron affinity)

Electronegativities tend to increase across a period Electronegativities tend to decrease down a

group or remain the same

•F most electronegative: 4.0 (Pauling scale)•Nitrogen, Oxygen, and Halogens most •Alkali and Alkali Earth metals least (1.0-0.7)•Values used in chemical BONDING

Periodic Table of ElectronegativitiesPeriodic Table of Electronegativities

Summation of Periodic TrendsSummation of Periodic Trends

Long Wavelength

=Low Frequency

=Low ENERGY

Short Wavelength

=High Frequency

=High ENERGY

Wavelength TableWavelength Table