1 Announcements & Agenda (01/22/07) You should currently be reading Ch 4! Quiz on Wednesday over Ch 3! Today: Radiation (Ch 9 – only responsible for notes)

11

AnnouncementsAnnouncements & Agenda& Agenda (01/22/07)(01/22/07)

You should currently be reading Ch 4!You should currently be reading Ch 4!Quiz on Wednesday over Ch 3!Quiz on Wednesday over Ch 3!

Today:Today: Radiation (Ch 9 – only responsible for notes)Radiation (Ch 9 – only responsible for notes) Electron energy levels (3.7)Electron energy levels (3.7) Periodic trends (3.3, 3.8)Periodic trends (3.3, 3.8)

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Last Time: All Atoms of the Same Last Time: All Atoms of the Same Element Have the Same # of Protons!!!Element Have the Same # of Protons!!!

1111

NaNa

11 protons

Symbol

Also, the # of protons = the # of electrons for Also, the # of protons = the # of electrons for a neutral atoma neutral atom

33

• represents a particular isotope of an element.represents a particular isotope of an element.

• gives the mass number in the upper left corner gives the mass number in the upper left corner and the atomic number in the lower left corner.and the atomic number in the lower left corner.

ExampleExample: An atom of sodium with atomic : An atom of sodium with atomic number 11 and a mass number 23 has the number 11 and a mass number 23 has the following atomic symbol:following atomic symbol:

mass number mass number 23 23 NaNa

atomic numberatomic number 1111

Last Time: Nuclear Symbols & IsotopesLast Time: Nuclear Symbols & Isotopes

protons + neutronsprotons + neutrons

44

Listed on the periodic tableListed on the periodic table

Gives the mass of “average” atom of each element Gives the mass of “average” atom of each element

compared to compared to 1212C C

Average atom based on all the isotopes and their Average atom based on all the isotopes and their

abundance %abundance %

Atomic mass (!unlike mass #!) is not a whole #Atomic mass (!unlike mass #!) is not a whole #

Na22.99

Last Time: The Atomic Mass is NOT Last Time: The Atomic Mass is NOT the Same as the Mass Numberthe Same as the Mass Number

55

Why Do We Care About Isotopes? Why Do We Care About Isotopes? Answer: Nuclear Stability!Answer: Nuclear Stability!

““belt of stability”belt of stability”

Unstable nucleiUnstable nuclei RadioactiveRadioactive Can decay to Can decay to

release alpha release alpha particles, beta particles, beta particles and particles and positrons.positrons.

66

Radiation Primer: Subatomic Radiation Primer: Subatomic Particles RevisitedParticles Revisited

Radiation comes from nucleus of an atomRadiation comes from nucleus of an atom

Unstable nucleus emits a particle or energyUnstable nucleus emits a particle or energy protons and/or neutrons typically lost from nucleus protons and/or neutrons typically lost from nucleus

changing identity of elementchanging identity of element

alpha (particle)alpha (particle)

beta (particle)beta (particle)

gamma (pure energy)gamma (pure energy)

77

Half-Life of a RadioisotopeHalf-Life of a Radioisotope

The The timetime for the radiation level to fall (decay) for the radiation level to fall (decay) to one-half its initial valueto one-half its initial value

decay curvedecay curve

8 mg8 mg 4 mg 4 mg 2 mg 1 mg2 mg 1 mg

initial

1 half-life 2 3

88

Examples of Half-LifeExamples of Half-Life

Isotope Half lifeIsotope Half life

C-15C-15 2.4 sec2.4 sec

Ra-224Ra-224 3.6 days3.6 days

Ra-223Ra-223 12 days12 days

I-125I-125 60 days60 days

C-14C-14 5700 years5700 years

U-235U-235 710 000 000 years710 000 000 years

99

Medical Uses of RadiationMedical Uses of Radiation

Nuclear medicine has two main arenasNuclear medicine has two main arenas Diagnostic methodsDiagnostic methods Small amounts of radioisotopes Small amounts of radioisotopes

administered to help image an organ or administered to help image an organ or follow a physiological processfollow a physiological process

Therapeutic methodsTherapeutic methods Larger radiation doses to deliver fatal Larger radiation doses to deliver fatal

punch to diseased tissuepunch to diseased tissue

1010

Diagnostic MethodsDiagnostic Methods

Radioisotopes behave chemically the Radioisotopes behave chemically the same as stable isotopes of the same same as stable isotopes of the same atomatom

Thus, can use to target an organ or a Thus, can use to target an organ or a physiological processphysiological process

Usually Usually -emitters because radiation -emitters because radiation has to emerge from the body if the has to emerge from the body if the imaging equipment is to see itimaging equipment is to see it

1111

Some Radio-Imaging IsotopesSome Radio-Imaging Isotopes

P-32P-32 Eye tumorsEye tumors

Cr-51Cr-51 Spleen shape and GI disordersSpleen shape and GI disorders

Fe-59Fe-59 Bone marrow functionBone marrow function

Se-75Se-75 Pancreas scanPancreas scan

I-131I-131 Thyroid malfunctionThyroid malfunction

Hg-197 Hg-197 Kidney scanKidney scan

1212

PET ScansPET Scans

PPositron ositron EEmission mission TTomographyomography

Good for following physiological processesGood for following physiological processes

Patient given short-lived Patient given short-lived ++-emitter-emitter

The The ++ hits an electron in tissues hits an electron in tissues

C11

6B

11

5e+

0

1+

- +

t1/2

20 min

1313

PET ScansPET Scans

With annihilation event, a pair of gamma rays With annihilation event, a pair of gamma rays are emitted in opposite directionsare emitted in opposite directions

Very clear images because signal distinguished Very clear images because signal distinguished from background radiation (only seen in one from background radiation (only seen in one direction)direction)

e- 0

-12 e+

0

1+

1414

A PET scan instrument places patient inside a ring A PET scan instrument places patient inside a ring of detectors to see the paired, 180of detectors to see the paired, 180oo gamma rays gamma rays

1515

PET ScansPET Scans

Can incorporate C-11 into a number of Can incorporate C-11 into a number of organic compounds to followorganic compounds to follow

Blood flowBlood flow

Glucose metabolismGlucose metabolism

Oxygen uptakeOxygen uptake

Find brain areas associated with epilepsyFind brain areas associated with epilepsy

Find hard to spot tumors Find hard to spot tumors

1616

Abnormal lymph nodes imaged by PET scan

Also: http://www.ldcmri.com/html/pet_scans.html

http://www.breastcancer.org/testing_pet.html

1717

Therapeutic RadiationTherapeutic Radiation

Selective destruction of pathological Selective destruction of pathological cells and tissuescells and tissues

Rapidly dividing cells most vulnerable - Rapidly dividing cells most vulnerable - thus it targets cancerthus it targets cancer

Used when cancer is not well localizedUsed when cancer is not well localized

Co-60 is common source of x-rays and Co-60 is common source of x-rays and -rays -rays

1818

Therapeutic RadiationTherapeutic RadiationCan also deliver a radiation dose with an Can also deliver a radiation dose with an internal administration of selected isotopesinternal administration of selected isotopes

I-131 targets thyroid cancer - thyroxine I-131 targets thyroid cancer - thyroxine contains iodinecontains iodine

I-125 crystals implanted in prostate gland to I-125 crystals implanted in prostate gland to deliver continuous radiation (tdeliver continuous radiation (t1/21/2 = 60 days) = 60 days)

Y-90 implanted in pituitary to slow tumor Y-90 implanted in pituitary to slow tumor growth everywheregrowth everywhere

1919

Radio-Tracer CompoundsRadio-Tracer Compounds

Huge use of radioisotopes to study Huge use of radioisotopes to study chemical reactionschemical reactions

Can see 10Can see 10-19-19g/L - almost individual atomsg/L - almost individual atoms Photosynthesis - carbon in glucose comes Photosynthesis - carbon in glucose comes

from COfrom CO22

Calcium - uptake is 90% efficient in Calcium - uptake is 90% efficient in children; 40% efficient in adultschildren; 40% efficient in adults

Zinc - uptake by trees in winter 2 ft/dayZinc - uptake by trees in winter 2 ft/day

2020

Shifting Gears…Shifting Gears…Electron Energy LevelsElectron Energy Levels

2121

Characteristics of ElectronsCharacteristics of Electrons

Extremely small massExtremely small mass

Located outside the nucleusLocated outside the nucleus

Moving at extremely high speeds Moving at extremely high speeds

roughly in a sphereroughly in a sphere

Form the “glue” that holds Form the “glue” that holds

compounds togethercompounds together

Have specific energy levelsHave specific energy levels

2222

Atomic SpectraAtomic Spectra

Atoms can Atoms can absorbabsorb and and emitemit radiation radiationAbsorptionAbsorption Usually, a source of white light passes Usually, a source of white light passes

through a sample, and the atoms absorb through a sample, and the atoms absorb only only specific frequenciesspecific frequencies of light. of light.

EmissionEmission When excited atoms emit photons, the When excited atoms emit photons, the

frequencies of the photon are frequencies of the photon are specificspecific.. ““quantization of energy”quantization of energy”

COOL DEMO…

2323

EMISSIONEMISSION

ABSORPTIONABSORPTION

2424

A ball on a staircase shows some properties of quantized energy states.

2525

Explanation for Discrete Explanation for Discrete Energies: the Bohr ModelEnergies: the Bohr Model

First model of the electron structure of atomsFirst model of the electron structure of atoms

Gives levels where an electron is most likely to Gives levels where an electron is most likely to be foundbe found

Incorrect today, but a key in understanding the Incorrect today, but a key in understanding the atomatom

2626

Bohr Model• Bohr noted the line spectra of certain elements

and assumed the electrons were confined to specific energy states. These were called orbits.

Line Spectra & the Bohr ModelLine Spectra & the Bohr Model

2727

Quantum MechanicsQuantum Mechanics

Describes the arrangement of electrons in Describes the arrangement of electrons in atoms in terms of:atoms in terms of: Main or principal energy levels (n)Main or principal energy levels (n) Can describe electrons with “quantum Can describe electrons with “quantum

numbers”numbers” Energy subshellsEnergy subshells Orbitals (space occupied within the atom)Orbitals (space occupied within the atom)

2828

Electron Levels (Shells)Electron Levels (Shells)

Contain electrons that are Contain electrons that are similarsimilar in energy in energy

and distance from nucleusand distance from nucleus

Low energy electrons are closest to the Low energy electrons are closest to the

nucleusnucleus

Identify by numbers 1, 2, 3, 4, 5, 6…..Identify by numbers 1, 2, 3, 4, 5, 6…..

The first shell (1) is lowest in energy, 2The first shell (1) is lowest in energy, 2ndnd level level

next and so on next and so on 1<2<3<41<2<3<4

2929

Number of Electrons Number of Electrons

Maximum number of electrons in any Maximum number of electrons in any electron level = 2nelectron level = 2n22

n =1n =1 2(2(11))22 = = 2 2

n =2n =2 2(2(22))22 == 8 8

n =3n =3 2(2(33))22 == 1818

3030

Order of Electron FillingOrder of Electron Filling

All electrons in the same energy level have All electrons in the same energy level have similarsimilar (BUT NOT IDENTICAL) energy. (BUT NOT IDENTICAL) energy.

Shell 1 Shell 1 2 electrons2 electrons

Shell 2Shell 2 8 electrons8 electrons

Shell 3Shell 3 18 electrons18 electrons (8 first,10 later)(8 first,10 later)

Order of filling for the first 20 electronsOrder of filling for the first 20 electrons

ShellShell 11 22 33 442e2e 8e8e 8e8e 2e2e

3131

Electron ConfigurationElectron Configuration

Lists the shells containing electronsLists the shells containing electronsWritten in order of increasing energyWritten in order of increasing energy

ElementElement ShellShell 1 1 22 33

HeHe 22

CC 22 44

FF 2 2 77

NeNe 2 2 88

AlAl 2 2 88 33

ClCl 22 8 8 77

3232

Learning CheckLearning Check

A. The electron configuration for sulfurA. The electron configuration for sulfur

1) 2,61) 2,6 2) 8,2,62) 8,2,6 3) 2, 8, 63) 2, 8, 6

B. The element in period 3 with two electrons B. The element in period 3 with two electrons in the outermost energy levelin the outermost energy level

1) Mg1) Mg 2) Ca2) Ca 3) Be3) Be

3333

Orbitals: “Locations” of the ElectronsOrbitals: “Locations” of the Electrons

• three-dimensional spaces around a nucleus three-dimensional spaces around a nucleus where an electron is most likely to be found. where an electron is most likely to be found.

• have shapes that represent electron density have shapes that represent electron density ((not a path the electron followsnot a path the electron follows).).

• each orbital can hold up to 2 electrons.each orbital can hold up to 2 electrons.

3434

ss Orbitals Orbitals

An An s orbital s orbital • has a spherical shape around has a spherical shape around

the nucleus.the nucleus.• is found in each energy level. is found in each energy level.

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

nn = 1 = 1

nn = 2 = 2

nn = 3 = 3

3535

pp Orbitals Orbitals

A A p orbitalp orbital • has a two-lobed shape.has a two-lobed shape.• is one of three is one of three pp orbitals in each energy level from n = 2. orbitals in each energy level from n = 2.


3636

Electrons in Energy Levels Electrons in Energy Levels nn = 1- 4 = 1- 4

Energy Orbitals Maximum Energy Orbitals Maximum Total Total Level Level No. of Electrons No. of Electrons ElectronsElectrons11 1 1ss 2 2 2222 2 2ss 2 2 88

22pp 6 633 3 3ss 2 2 1818

33pp 6 6 33dd 1010

44 4 4ss 2 2 3232 44pp 6 6 44dd 1010

44ff 1414

3737

Organization of the Periodic TableOrganization of the Periodic Table

ss11 s s22 p p11 p p2 2 pp3 3 pp44 p p55

pp66

112233 dd11 - d - d1010

445566

f1 - f14

3838

Periodic LawPeriodic Law

All the elements in a group have the same electron All the elements in a group have the same electron configuration in their outermost shellsconfiguration in their outermost shells

Outermost electrons are called Outermost electrons are called valence electronsvalence electrons

Elements with same # of valence electrons display Elements with same # of valence electrons display similar chemical & physical properties!!!similar chemical & physical properties!!!

Example: Example: Group 2Group 2

BeBe 2, 2, 22

Mg 2, 8, Mg 2, 8, 22

Ca Ca 2, 2, 8, 2, 2, 8, 22

3939

Groups and PeriodsGroups and Periods

4040

Periodic TablePeriodic Table

Note: Two methods for numbering; we will use Note: Two methods for numbering; we will use 1A, 2A, etc.1A, 2A, etc.

4141

Metals, Nonmetals, and MetalloidsMetals, Nonmetals, and Metalloids

The heavy zigzag line The heavy zigzag line separates metals and separates metals and nonmetals.nonmetals.• MetalsMetals are located to are located to

the left.the left.• NonmetalsNonmetals are located are located

to the right. to the right. • MetalloidsMetalloids are located are located

along the heavy along the heavy zigzag line between zigzag line between the metals and the metals and nonmetals.nonmetals.


4242

MetalsMetals • shiny and ductileshiny and ductile• good conductors of heat and electricitygood conductors of heat and electricity

NonmetalsNonmetals• dull, brittle, and poor conductorsdull, brittle, and poor conductors• good insulatorsgood insulators

MetalloidsMetalloids• better conductors than nonmetals, but not as good better conductors than nonmetals, but not as good

as metalsas metals• used as semiconductors and insulatorsused as semiconductors and insulators

Metals, Nonmetals, & MetalloidsMetals, Nonmetals, & Metalloids

4343

More Periodic TrendsMore Periodic Trends

How Atomic Orbital filling affects:How Atomic Orbital filling affects: Atomic Size (Radius)Atomic Size (Radius) Ionization Energy Ionization Energy

Definitions….Definitions….

Ionization Energy : Cost of removing an eIonization Energy : Cost of removing an e-- from a neutral atomfrom a neutral atom

Atomic Radii: Distance between center of Atomic Radii: Distance between center of nucleus and outer electron shellnucleus and outer electron shell

4444

Atomic Radius Within A GroupAtomic Radius Within A Group

Atomic radius Atomic radius increasesincreases going down each group going down each group of representative of representative elements.elements.


4545

Atomic Radius Across a PeriodAtomic Radius Across a Period

Going across a period left to right, Going across a period left to right, • an increase in number of protons increases attraction for an increase in number of protons increases attraction for

valence electrons.valence electrons.• atomic radius atomic radius decreasesdecreases..


4646

Ionization Energy In a GroupIonization Energy In a Group

Going up a group ofGoing up a group ofrepresentative elements,representative elements,• the distance decreases the distance decreases

between nucleus and between nucleus and valence electrons.valence electrons.

• the ionization energy the ionization energy increases.increases.


4747

Ionization EnergyIonization Energy

• Metals have Metals have lower lower ionization ionization energies.energies.

• Nonmetals Nonmetals have higher have higher ionization ionization energiesenergies. .


Documents

1 Announcements & Agenda (01/22/07) You should currently be reading Ch 4! Quiz on Wednesday over Ch 3! Today: Radiation (Ch 9 – only responsible for notes)