Chapter 4/25 Chapter 4/25

Atomic StructureAtomic Structure

Nuclear ChemistryNuclear Chemistry

A Long, Long Time A Long, Long Time Ago…Ago… Greek Philosophers- 4 elements Greek Philosophers- 4 elements

are Earth, Water, Fire, and Airare Earth, Water, Fire, and Air Aristotle- first recorded atomic Aristotle- first recorded atomic

thoughtsthoughts Matter is continuous (no atoms)Matter is continuous (no atoms)

Democritus (400 B.C.) - first Democritus (400 B.C.) - first recorded atomic theoryrecorded atomic theory

Atoms are smallest part of matter, each Atoms are smallest part of matter, each type of matter has different atomstype of matter has different atoms

Aristotle and Aristotle and DemocritusDemocritus

A Long Time Ago…A Long Time Ago…

Antoine Lavoisier (1782)Antoine Lavoisier (1782)– Used experiments in closed containers to Used experiments in closed containers to

develop the LCMdevelop the LCM Joseph Proust (1799)Joseph Proust (1799)

– Analyzed water to develop the Law of Analyzed water to develop the Law of Definite ProportionsDefinite Proportions

John Dalton (1803)John Dalton (1803)– Compiled past research to develop the Compiled past research to develop the

first useful atomic theoryfirst useful atomic theory

Lavoisier and ProustLavoisier and Proust

John DaltonJohn Dalton

Dalton’s theory Dalton’s theory had 4 major tenetshad 4 major tenets

1.1. All matter is All matter is composed of atomscomposed of atoms

2.2. Atoms are Atoms are indivisibleindivisible

3.3. Atoms of 1 element Atoms of 1 element are alike, but are alike, but different from those different from those of other elementsof other elements

4.4. Atoms combine in Atoms combine in small, whole small, whole number ratios to number ratios to form compoundsform compounds

A ReminderA Reminder

Observation, Observation, Observation, Observation, ObservationObservation

ResearchResearch HypothesisHypothesis Experiment, Revise hypothesis lots Experiment, Revise hypothesis lots

of timesof times Results match….may become a Results match….may become a

theorytheory

A Little While Ago…A Little While Ago…

1897- J.J. 1897- J.J. Thomson Thomson discovers the discovers the electron using a electron using a cathode ray tubecathode ray tube

Cathode Ray Tube Cathode Ray Tube ExperimentExperimenthttp://www.aip.org/history/electron/jjappara.htm

The Nucleus Exists!The Nucleus Exists!

1911- Ernest 1911- Ernest Rutherford uses Rutherford uses the gold foil the gold foil experiment to experiment to “discover” the “discover” the nucleusnucleus

The Gold Foil The Gold Foil ExperimentExperiment

Results of Gold Foil Results of Gold Foil Experiment…Experiment… http://online.cctt.org/physicslab/content/Phy1

/lessonnotes/atomic/atomicmodelsandspectra.asp

http://micro.magnet.fsu.edu/electromag/java/rutherford/

Over 98% of the particles went straight Over 98% of the particles went straight throughthrough

About 2% of the particles went through About 2% of the particles went through but were deflected by large anglesbut were deflected by large angles

About 0.01% of the particles bounced About 0.01% of the particles bounced off the gold foiloff the gold foil

Rutherford’s Rutherford’s ConclusionConclusion

Rutherford's Nuclear ModelRutherford's Nuclear Model

1. The atom contains a tiny dense 1. The atom contains a tiny dense center called the nucleuscenter called the nucleus – the volume is about 1/10 trillionth the the volume is about 1/10 trillionth the

volume of the atom volume of the atom 2. The nucleus is essentially the 2. The nucleus is essentially the

entire mass of the atomentire mass of the atom 3. The nucleus is positively charged3. The nucleus is positively charged

– the amount of positive charge of the the amount of positive charge of the nucleus balances the negative charge of the nucleus balances the negative charge of the electrons electrons

4. The electrons move around in the 4. The electrons move around in the empty space of the atom empty space of the atom surrounding the nucleussurrounding the nucleus

Coworker James Chadwick later Coworker James Chadwick later adds neutronsadds neutrons

Understanding Understanding Periodic BlocksPeriodic Blocks

19 19

KK

39.098339.0983

Atomic NumberAtomic Number– # of protons# of protons

Element SymbolElement Symbol

Mass NumberMass Number– Protons + Protons +

NeutronsNeutrons

Can 20.0983 Neutrons Can 20.0983 Neutrons Exist???Exist??? No, 39.0983 is an average mass No, 39.0983 is an average mass

of all natural K atomsof all natural K atoms– All K atoms MUST have 19 protonsAll K atoms MUST have 19 protons– Some have 20 neutrons, some 19, Some have 20 neutrons, some 19,

some 21…some 21…– Average is 20.0983 neutronsAverage is 20.0983 neutrons– Individual isotopes are identified by Individual isotopes are identified by

the number of the number of neutronsneutrons

Identifying Protons, Identifying Protons, Neutrons, and Neutrons, and ElectronsElectrons Chlorine-35 (element-mass number)Chlorine-35 (element-mass number) # of protons = 17# of protons = 17 # electrons = # protons# electrons = # protons # neutrons = mass number – protons# neutrons = mass number – protons

– 35-17 = 1835-17 = 18 Why no electrons in atomic mass?Why no electrons in atomic mass?

– Electron has mass 1/1837 of Proton and Electron has mass 1/1837 of Proton and NeutronNeutron

Nuclear symbol notationNuclear symbol notation (nuclide (nuclide symbols)symbols)– Example: Example: 2727

1313Al or Al or 2727AlAl

– # protons = ______# protons = ______– # neutrons = ______# neutrons = ______– # electrons = ______# electrons = ______

Problems that ariseProblems that arise– Charges and IonsCharges and Ions: only changes the : only changes the

number of electrons!number of electrons!– Finding mass numberFinding mass number: use symbol, # p+ : use symbol, # p+

and nand noo, or periodic table IN THAT ORDER!, or periodic table IN THAT ORDER!

Atomic Mass UnitsAtomic Mass Units

Carbon-12Carbon-12– 6 protons6 protons– 6 neutrons6 neutrons

1 amu = 1/12 mass of a C-12 1 amu = 1/12 mass of a C-12 atomatom

Nuclear Stability- too Nuclear Stability- too many neutrons or many neutrons or protons causes protons causes instabilityinstability

Chemical vs. Nuclear Chemical vs. Nuclear ChangeChange

Chemical ChangeChemical Change- produces new kinds of - produces new kinds of matter with new propertiesmatter with new properties– Involves breaking and forming BONDSInvolves breaking and forming BONDS– Accomplished by rearrangement of Accomplished by rearrangement of

ELECTRONSELECTRONS Nuclear ChangeNuclear Change- produces a new nucleus - produces a new nucleus

that contains less energythat contains less energy– Involves emission or capture of nuclear Involves emission or capture of nuclear

particlesparticles– Accomplished by changing PROTONS Accomplished by changing PROTONS

and NEUTRONS in nucleusand NEUTRONS in nucleus

Nuclear DecayNuclear Decay

Nuclear ParticlesNuclear Particles– Alpha- rapidly moving He nuclei with Alpha- rapidly moving He nuclei with

a (+) chargea (+) charge– Beta – rapidly moving electrons with Beta – rapidly moving electrons with

a (-) chargea (-) charge– Gamma – rapidly moving Gamma – rapidly moving

electromagnetic radiation with no electromagnetic radiation with no mass or chargemass or charge

HighHighMedMedLowLowActual Actual HazardHazard

Low-MedLow-MedMedMedHighHighBiological Biological HazardHazard

LowLowMedMedHighHighEnergyEnergy

Hard (2 cm Hard (2 cm lead)lead)

Medium Medium (aluminum (aluminum

foil)foil)

Easy Easy

(skin/(skin/clothes)clothes)

ShieldingShielding

0000γγ00

-1-1ee4422HeHeSymbolSymbol

GAMMA (GAMMA (γγ))BETA (BETA (ββ))ALPHA (ALPHA (αα))

Other RadiationOther Radiation

Ionizing Radiation- has significant Ionizing Radiation- has significant energy to change atoms and energy to change atoms and molecules into ionsmolecules into ions

– Types: alpha, beta, gamma, x-raysTypes: alpha, beta, gamma, x-rays– Effects to living organisms: changes in, DNA (cell Effects to living organisms: changes in, DNA (cell

death/cancer)death/cancer)

Nonionizing radiation- does not have Nonionizing radiation- does not have significant energy to ionize atoms or significant energy to ionize atoms or molecules (types: microwaves, visible molecules (types: microwaves, visible light, radiowaves)light, radiowaves)

Nuclear ReactionsNuclear Reactions

– Transmutation- Changing the Transmutation- Changing the nucleus of the atom to create a nucleus of the atom to create a new elementnew element

– How is a Nuclear Equation Written?How is a Nuclear Equation Written? Parent nuclide- initial nucleus that Parent nuclide- initial nucleus that

undergoes changesundergoes changes Daughter nuclide- nucleus resulting Daughter nuclide- nucleus resulting

from decay of parentfrom decay of parent

Types of Nuclear Types of Nuclear ReactionsReactions Alpha Emission- generally occurs if Alpha Emission- generally occurs if

nucleus has too many protons and nucleus has too many protons and neutronsneutrons

Beta Emission- results from conversion Beta Emission- results from conversion of neutron to proton and occurs if of neutron to proton and occurs if nucleus has too many neutronsnucleus has too many neutrons

Positron Emission- results from Positron Emission- results from conversion of proton to neutron and conversion of proton to neutron and occurs if nucleus has too few neutronsoccurs if nucleus has too few neutrons

Gamma Emission- often accompanies Gamma Emission- often accompanies other decay processesother decay processes

Example: Alpha DecayExample: Alpha Decay

2522529999Es Es ______ + ______ + 44

22HeHe

Radioactive Decay Radioactive Decay Half-livesHalf-lives

Half-life is the time taken for Half-life is the time taken for half of the atoms of a radio-half of the atoms of a radio-active substance to decay.active substance to decay.

Half-lifeHalf-life

Half-lives can Half-lives can range from a range from a millionth of a millionth of a second to second to millions of yearsmillions of years

Radioactive DatingRadioactive Dating

Uses carbon-14 to tell age of Uses carbon-14 to tell age of fossilsfossils

C-14 is present constantly in C-14 is present constantly in atmosphereatmosphere

15.3 decays/min in living organism15.3 decays/min in living organism decays/min decreases by ½ every decays/min decreases by ½ every

5370 years an organism is dead.5370 years an organism is dead. Only useful to 60,000 yrs agoOnly useful to 60,000 yrs ago

TracersTracers

Radioactive isotopes used to Radioactive isotopes used to track pathwaystrack pathways

Chemistry/biology- pathways of Chemistry/biology- pathways of reactions reactions

Industry and environment- path of Industry and environment- path of groundwater, durability of containersgroundwater, durability of containers

Medicine- diagnose malfunctionsMedicine- diagnose malfunctions

Nuclear Reactions for Nuclear Reactions for EnergyEnergy

Fission- nucleus Fission- nucleus broken into 2 broken into 2 smaller nucleismaller nuclei

Fusion- smaller Fusion- smaller nuclei join to nuclei join to form a larger, form a larger, more stable more stable nucleinuclei

Reactants and Reactants and ProductsProducts Fission- Fission- 9292

235235U fuel U fuel used in a chain used in a chain reactionreaction

– Limited resourceLimited resource– critical mass- critical mass-

minimum mass to minimum mass to sustain chain sustain chain reactionreaction

– Risk of runaway Risk of runaway chain reactionchain reaction

– Produces Produces radioactive waste radioactive waste productsproducts

– Disposal concernsDisposal concerns– Reaction: Reaction:

Fusion- Fusion- 1122H and H and 11

33H H used as fuelused as fuel

– extracted from sea extracted from sea waterwater

– not a chain reactionnot a chain reaction– No risk of runaway No risk of runaway

reaction reaction – Nonradioactive Nonradioactive

waste: helium waste: helium – Problem: Problem: needs temp needs temp

of 200 Million Kof 200 Million K– Reaction:Reaction:

Nuclear Power- Nuclear Power- generated generated by a by a controlled controlled fissionfission chain chain reactionreaction

Control rods- absorb Control rods- absorb neutrons to slow neutrons to slow the chain reactionthe chain reaction

Made of cadmiumMade of cadmium Inserted or Inserted or

withdrawn to keep withdrawn to keep temp of reaction temp of reaction steadysteady

Moderators- slow Moderators- slow neutrons down so neutrons down so they DO hit they DO hit uranium fuel rods uranium fuel rods

Made of water, Made of water, beryllium, or beryllium, or graphitegraphite

Intended to allow Intended to allow neutrons to be neutrons to be absorbed by absorbed by uraniumuranium

Cooling and ShieldingCooling and Shielding

Water- acts as a coolant and Water- acts as a coolant and transfers heat between reactor transfers heat between reactor and turbines that produce and turbines that produce electricityelectricity

Steel & concrete- surround core Steel & concrete- surround core and protect personnel by and protect personnel by absorbing radiationabsorbing radiation

Nuclear MeltdownsNuclear Meltdowns

Cherynobyl (Soviet Cherynobyl (Soviet Union, 1986)Union, 1986)

– Runaway fission Runaway fission reaction from core reaction from core meltdownmeltdown

– Radiation escaped Radiation escaped to atmosphereto atmosphere

– 31 dead, estimated 31 dead, estimated 15,000 cancer 15,000 cancer deaths in next 50 deaths in next 50 yearsyears

Three Mile Island Three Mile Island (Pennsylvania, (Pennsylvania, 1979)1979)– partial meltdownpartial meltdown– contained before contained before

widespread damageswidespread damages