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AnnouncementsAnnouncements & Agenda& Agenda (01/19/07)(01/19/07)

You should currently be reading Ch 3 & starting You should currently be reading Ch 3 & starting Ch 4, which will be relevant to lab next weekCh 4, which will be relevant to lab next week

Today:Today: More on Subatomic Particles (3.5)More on Subatomic Particles (3.5) Isotopes & Atomic Mass (3.6)Isotopes & Atomic Mass (3.6) Radiation (Ch 9 – only responsible for notes)Radiation (Ch 9 – only responsible for notes)

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I thought the quiz was…I thought the quiz was…

11 22 33 44 55

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0% 1.1. A piece of cake.A piece of cake.

2.2. Manageable.Manageable.

3.3. Not too easy or difficult (what I expected).Not too easy or difficult (what I expected).

4.4. Challenging!Challenging!

5.5. Oh my goodness!!!Oh my goodness!!!

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Last Time: Classification of MatterLast Time: Classification of Matter

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Last Time: Know These ElementsLast Time: Know These Elements

OO 65.0 %65.0 % KK 0.34 0.34CC 18.018.0 SS 0.26 0.26HH 10.010.0 NaNa 0.14 0.14NN 3.0 3.0 ClCl 0.14 0.14CaCa 1.4 1.4 FeFe 0.004 0.004PP 1.0 1.0 ZnZn 0.003 0.003 MgMg 0.50 0.50

Trace ElementsTrace ElementsAs, Cr, Co, Cu, F, I, Mn, Mo, Ni, Se, Si, VAs, Cr, Co, Cu, F, I, Mn, Mo, Ni, Se, Si, V

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Methane (CH4) reacts with oxygen (O2) to produce carbon dioxide (CO2) and water (H2O). COUNT THE ATOMS!

SEE BOB DEMO!

Last Time: Atoms Last Time: Atoms RearrangeRearrange in Chemical in Chemical ReactionsReactions

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Subatomic ParticlesSubatomic Particles

Atoms contains subatomic particles,Atoms contains subatomic particles,

• protons protons have a positive (+) charge.have a positive (+) charge.

• electrons electrons have a negative (-) charge.have a negative (-) charge.• like charges like charges repelrepel and unlike charges and unlike charges attractattract..

• neutronsneutrons are neutral. are neutral.

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Structure of the AtomStructure of the Atom

• dense nucleus that dense nucleus that contains protons and contains protons and neutrons.neutrons.

• of electrons in a of electrons in a large empty space large empty space around the nucleus.around the nucleus.

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Atomic Mass ScaleAtomic Mass Scale

On the atomic mass scale for subatomic particles,On the atomic mass scale for subatomic particles,

• 1 atomic mass unit (amu) has a mass equal to 1/12 of 1 atomic mass unit (amu) has a mass equal to 1/12 of the mass of the carbon-12 atom.the mass of the carbon-12 atom.

• a proton has a mass of about 1 (1.007) amu.a proton has a mass of about 1 (1.007) amu.

• a neutron has a mass of about 1 (1.008) amu.a neutron has a mass of about 1 (1.008) amu.

• an electron has a very small mass, 0.000549 amu.an electron has a very small mass, 0.000549 amu.

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SummarySummary

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Atomic Number = The Identity of Atomic Number = The Identity of the Elementthe Element

Counts the number Counts the number

of of

protonsprotons

in an atomin an atom

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All Atoms of the Same Element All Atoms of the Same Element Have the Same # of Protons!!!Have the Same # of Protons!!!

1111

NaNa

11 protons

Symbol

12www.webelements.com

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An atom of An atom of • an element is electrically neutral; the net charge of an element is electrically neutral; the net charge of

an atom is zero.an atom is zero.• has an equal number of protons and electrons. has an equal number of protons and electrons.

number of protons = number of electronsnumber of protons = number of electrons

Aluminum has 13 protons and 13 electrons. The net Aluminum has 13 protons and 13 electrons. The net charge is zero. charge is zero.

13 protons (13+) + 13 electrons (13 -) = 013 protons (13+) + 13 electrons (13 -) = 0

Electrons in An AtomElectrons in An Atom

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Mass NumberMass Number

Since protons and neutrons account for most Since protons and neutrons account for most of the mass of the atom, of the mass of the atom,

count the number count the number

of of

protons and neutronsprotons and neutrons

to determine the mass number!!!to determine the mass number!!!

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

Nuclear SymbolNuclear Symbol

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Subatomic Particles ExampleSubatomic Particles Example

1616 3131 6565 OO P P Zn Zn

88 1515 3030

? p? p++ ? p? p++ ? p? p++

? n? n ? n? n ? n? n? e? e-- ?? ee-- ? e? e--

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Subatomic Particles ExampleSubatomic Particles Example

1616 3131 6565 OO P P Zn Zn

88 1515 3030

8 p8 p++ ? p? p++ ? p? p++

8 n8 n ? n? n ? n? n8 e8 e-- ?? ee-- ? e? e--

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Subatomic Particles ExampleSubatomic Particles Example

1616 3131 6565 OO P P Zn Zn

88 1515 3030

8 p8 p++ 15 p15 p++ ? p? p++

8 n8 n 16 n16 n ? n? n8 e8 e-- 1515 ee-- ? e? e--

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Subatomic Particles ExampleSubatomic Particles Example

1616 3131 6565 OO P P Zn Zn

88 1515 3030

8 p8 p++ 15 p15 p++ 30 p30 p++

8 n8 n 16 n16 n 35 n35 n8 e8 e-- 1515 ee-- 30 e30 e--

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IsotopesIsotopes

Atoms with the same number of protons, but Atoms with the same number of protons, but

different numbers of neutrons. different numbers of neutrons.

Atoms of the same element (same atomic Atoms of the same element (same atomic

number) with different mass numbersnumber) with different mass numbers

Isotopes of chlorineIsotopes of chlorine

3535ClCl 3737ClCl1717 1717

chlorine - 35 chlorine - 37chlorine - 35 chlorine - 37

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Learning Check Learning Check

An atom of zinc has a mass number of 65.An atom of zinc has a mass number of 65.

A.A. Number of protons in the zinc atomNumber of protons in the zinc atom

1) 301) 30 2) 352) 35 3) 653) 65

B.B. Number of neutrons in the zinc atomNumber of neutrons in the zinc atom

1) 301) 30 2) 352) 35 3) 653) 65

C. What is the mass number of a zinc isotope C. What is the mass number of a zinc isotope

with 37 neutrons?with 37 neutrons?

1) 371) 37 2) 652) 65 3) 673) 67

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Atomic MassAtomic Mass

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

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Calculating Atomic MassCalculating Atomic Mass

Percent(%) abundance of isotopesPercent(%) abundance of isotopes

Mass of each isotope of that elementMass of each isotope of that element

Weighted average =Weighted average =

((mass isotopemass isotope1 1 x x %%)) + ( + (mass isotopemass isotope2 2 x x %%)) + … + …

100 100 100 100

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Example: Atomic Mass of Mg Example: Atomic Mass of Mg

Isotopes Isotopes Mass of Isotope Abundance Mass of Isotope Abundance 2424Mg Mg == 24.0 amu 24.0 amu 78.70%78.70%

2525Mg Mg = = 25.0 amu 25.0 amu 10.13%10.13%

2626Mg Mg = = 26.0 amu26.0 amu 11.17%11.17%

Atomic mass (average mass) Mg = 24.3 amuAtomic mass (average mass) Mg = 24.3 amu

Mg24.3

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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.

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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

αα alpha (particle)alpha (particle)

ββ beta (particle)beta (particle)

γγ gamma (pure energy)gamma (pure energy)

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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

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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

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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

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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 γγ-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

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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 ββ++-emitter-emitter

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

C11

6B

11

5e+

0

1+

- β+

t1/2

20 min

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PET ScansPET Scans

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

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

e- 0

-12 γe+

0

1+

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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

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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 metabolism (Fig 9E.5, Page Glucose metabolism (Fig 9E.5, Page 259)259)

Oxygen uptakeOxygen uptake

Find brain areas associated with epilepsyFind brain areas associated with epilepsy

Find hard to spot tumors Find hard to spot tumors

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Abnormal lymph nodes imaged by PET scan

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

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

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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 γγ-rays -rays

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Therapeutic RadiationTherapeutic Radiation

Can also deliver a radiation dose with Can also deliver a radiation dose with an internal administration of selected an internal administration of selected isotopesisotopes

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

I-125 crystals implanted in prostate I-125 crystals implanted in prostate gland to deliver continuous radiation (tgland to deliver continuous radiation (t 1/21/2

= 60 days)= 60 days)

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

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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 g/L - almost individual atomsatoms

Photosynthesis - carbon in glucose Photosynthesis - carbon in glucose comes from COcomes from 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