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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
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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
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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.
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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.
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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.
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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..
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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.
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
4747
Ionization EnergyIonization Energy
• Metals have Metals have lower lower ionization ionization energies.energies.
• Nonmetals Nonmetals have higher have higher ionization ionization energiesenergies. .
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings