chemistry day 9

Chemistry Day 9 Monday, September 23rd – Tuesday,

September 24th, 2019

Do-Now Title: “Brainstorm: Unit 1” 1.  Write down today’s FLT 2.  Draw what an atom looks like according to

Democritus and Dalton 3.  Draw what an atom looks like according to J.J.

Thomson 4.  Draw what an atom looks like according to Ernest

Rutherford 5.  Use one of the pro-talk sentence frames to tell me

something we have learned about atoms or subatomic particles.

6.  Underneath your do-now, write “Brainstorm list” and number 1-20

Finished? Take out your planner and table of contents.

FLT •  I will be able to calculate the mass

number and number of neutrons in an atom by completing Atoms CN

Standard HS-PS1-8:Developmodelstoillustratethechangesinthecompositionofthenucleusoftheatomandtheenergyreleasedduringtheprocessesoffission,fusion,andradioactivedecay

Distinguishing Among Atoms

Guiding Questions •  Whatmakeselementsandisotopesdifferent?•  Howcanwecalculatethenumberofneutronsinanatom?

•  HowcanIcalculatetheatomicmassofanelement?

•  CanIexplainwhychemistsusetheperiodictable?

Recall •  An atom’s atomic number (Z) = the number

of protons in the nucleus. Defines element.

Recall •  Elementsaredifferentbecausetheycontaindifferentnumbersofprotonsàifyouchangethenumberofprotons,youchangetheelement

Recall •  Atoms are

electrically neutral •  Protonshavea+1charge

•  Whatbalancesthem?•  Electronshavea-1charge

•  Therefore,protons=electronsinanatom

Groups have similar properties GroupsaretheVERTICALCOLUMNS

Mass Number •  Recall:

– Protonshavearelativemassof1

– Neutronshavearelativemassof1

– Electronshavearelativelyinsignificantmass

Mass Number •  Massnumber=p++n0•  Copy and complete the table below

Nuclide p+ n0 e- Mass #

Oxygen -

10

- 33 42

- 31 15

8 8 1818

Shorthand Notation MassNumber

AtomicNumber

Symbol

Shorthand Notation ■  Find each of these:

a)  number of protons

b)  number of neutrons

c)  number of electronsd)  Atomic number

e)  Mass Number C 14

6

Shorthand Notation ■  If an element has an atomic number of

34 and a mass number of 78, what is the: a)  number of protonsb)  number of neutrons

c)  number of electronsd)  shorthand notation

Isotopes •  What was Dalton mistaken about? •  Dalton was also wrong about all elements of

the same type being identical

Isotopes •  Atoms of the same element can have

different numbers of neutrons.•  Thus, different mass numbers.•  These are called isotopes.

Isotopes •  FrederickSoddy(1877-1956)proposedtheideaofisotopesin1912

•  Isotopes=atomsofthesameelementhavingdifferentmasses,duetovaryingnumbersofneutrons.

•  SoddywontheNobelPrizeinChemistryin1921forhisworkwithisotopesandradioactivematerials.

Isotopes

• We can also put the mass number after the name of the element: – carbon-12 – carbon-14 – uranium-235

Isotopes Isotope Protons Electrons Neutrons Nucleus

Hydrogen–1

(protium)

1

1

0

Hydrogen-2

(deuterium)

1

1

1

Hydrogen-3

(tritium)

1

1

2

Isotopes

• Elements occur in nature as mixtures of isotopes.

Atomic Mass § Howheavyisanatomofoxygen?§ Itdepends,becausetherearedifferentkindsofoxygenatoms.

§ Wearemoreconcernedwiththeaverageatomicmass.

§ Averageatomicmass=weightedaverageoftheisotopesofagivenelementbasedonthepercentabundanceinnature

Atomic Mass • Each isotope has its own atomic

mass, thus we determine the average from percent abundance.

Calculating Atomic Mass • Multiply the atomic mass of

each isotope by its abundance (expressed as a decimal), then add the results.

•  If not told otherwise, the mass of the isotope is expressed in atomic mass units (amu)

Example Anelementhasthefollowingnaturalabundancesandisotopicmasses:90.92%abundancewith19.99amu,0.26%abundancewith20.99amu,and8.82%abundancewith21.99amu.Calculatetheaverageatomicmassofthiselement.Solution:Averageatomicmass=(0.9092×19.99amu)+(0.0026×20.99amu)+(0.0882×21.99amu)Averageatomicmass=20.17amuMakesuretoshowworkandunitsJ

Pair-Share-Respond 1.  What is Z? 2.  Can atoms of the same element have

different numbers of protons? 3.  Discuss all information you can

derive from the shorthand notation pictured

4.  Explain how isotopes differ from one another.

5. What is meant by the term “average atomic mass”?

Chemistry Day 10 Wednesday, September 25th – Thursday,

September 26th, 2019

Do-Now Title: “Nuclear Notation Review” 1.  Answer the do-now questions on your

worksheet 2.  If you finish early, you may start on the back.

Otherwise, it is part of our classwork. You may not work on it once we start our announcements.

Finished? Take out your planner and table of

contents.

FLT •  I will be able to describe the three main

types of nuclear radiation by completing Ch. 19 CN A

Standard HS-PS1-8:Developmodelstoillustratethechangesinthecompositionofthenucleusoftheatomandtheenergyreleasedduringtheprocessesoffission,fusion,andradioactivedecay

Ch. 19 Part A: Radiation

Review–AtomicModels

Nucleons and Nuclear Forces

SubatomicParticles•  In1932,JamesChadwickdiscoveredtheneutron

•  Thiswasimportantinimprovingtheproton-electronatomicmodel

•  Newmodel:Theproton-neutronnucleus

Proton-NeutronModel

SubatomicParticles•  Wenowhavethreesubatomicparticles:– Protonsp+– Electronse-– Neutronsn0

•  Nucleons=subatomicparticleslocatedinthenucleusofatoms(p+andn0)– Nucleonsarecomposedofsmallerparticlescalledquarks

Forces•  Therearetwomainforcesatplayinournucleus:

–  Electromagneticforce(proton-protonrepulsion)–  Strongforce(nucleonssticktogether)

Forces•  Notallnucleiarestable

–  Positively-chargedprotonscanrepeleachother•  StrongNuclearForce=bindsp+andn0togetherinthenucleus

Unstable Nuclei – Strongforce=holdsnucleitogetherovershortdistances

– Largernucleicanbemoreunstable

Nuclear Stability

NuclearStability•  StrongNuclearForce

– Thisforcecanonlyactoververyshortdistances– Itisthestrongestattractiveforce(137timesmorethanelectromagnetic)

– Overextremelyshortdistances,thestrongnuclearforceoverridestherepulsionoftheelectromagneticforce

•  Lookingattheratioofprotonstoneutronscanhelpusdeterminethestabilityofthenucleus

Band of Stability

•  The region on a graph which indicates all stable nuclei when the number of neutrons are compared to the number of protons for all stable nuclei

NuclearStability•  Largernuclidestendtobemoreunstable

– Allnuclideswithmorethan83protons(bismuth)areunstable

•  Mostnuclideswanta1:1ofneutrons:protons– Heaviernuclidesneedmoreneutrons

Pair-Share-Respond 1. Whatarenucleons?2. Explainthetypesofforcesoccurringwithinanucleus

3. Describetwodifferenttypesofnucleithatareunstable

Radioactivity

Radioactivity

•  Howdoesanunstablenucleusreleaseenergy?

Context •  MarieCurie(1867-1934)helpeddiscovernewelements(PoloniumandRadium),aswellasradioactiveelements

•  Curiestudiedmaterialsthatgaveoffrays,whichshecalledradioactivity

Radiation •  Radiation=Rays&particlesemittedbyaradioactivesource

Radiation Radioisotopes=unstableisotopeswhosenucleiundergochangestobecomemorestable

Radioactivity

– Anunstablenucleus“decays”intoanewnucleusbychangingitsnumberofprotonsspontaneously

– Ifthenumberofprotonschanges,isitthesameelementanymore?

Radioactivity – Radioactivedecay=unstablenucleusreleasesenergy/emitsradiation

Types of Radiation

Types of Radiation

What are the three main types of nuclear radiation?

Main Types of Radiation

1.  Alpha (α) Radiation 2.  Beta (β) Radiation 3. Gamma (Υ) Radiation

Alpha Radiation Alpha radiation = Emits alpha particles (helium) •  Mass number decreases by 4, atomic number

decreases by 2

Alpha Radiation Ex/

Beta Radiation

•  Beta Radiation = Emits a beta particle (electron) – Mass number stays the same. Atomic number increases by

1.

Beta Radiation Ex/

Gamma Radiation

•  Gamma radiation = Emits a high-E photon(gamma ray).

•  Tends to accompany other nuclear decay processes

Types of Radiation

•  Alphaparticlesaretheleastpenetrating.Gammaraysarethemostpenetrating.

Figure4.2:Thepenetratingpowerofradiation.

© 2003 John Wiley and Sons Publishers

Arethereothertypesofdecay?

α-particleproduction

Spontaneousfission

β-particleproduction

Positronproduction

γ-rayproduction

Positron Production

•  Positron = positively charged anti-electron

Pair-Share-Respond 1. Whatareradioisotopes?2. Whatareourthreemaintypesof

radiation?3. Whichtypeisthemostdangerous?4. Whatisemittedinbetadecay?5. Whatisemittedinalphadecay?

Chemistry Day 11 Friday, September 27th, 2019

Do-Now Title: “BrainPOP: Radioactivity” 1.  Write down today’s FLT 2.  What is your current grade in this class? 3.  Is your grade where you want it to be? If not,

what will you do to change it? 4.  What is the most difficult part of this class so

far? 5.  Define the term “radioisotope”. Even better if

you can do it without referring to the notes. 6.  Underneath your do-now, write “brainpop

practice” and number 1-10 Finished? Take out your planner and table of

contents.

Add to do-now paper: 1.  Use a pro-talk sentence frame to tell me

something about radioactivity. 2.  You have isolated one kilogram of pure Mobium,

a new radioactive substance. When Mobium decays, it becomes ordinary iron. You have a sample of 25 grams.

a.  You wrap the sample in paper, and observe that radiation is no longer detectable. What kind of radiation is it (possibly) emitting?

b.  After 6 hours, you notice that only 12.5 grams remain. Explain what happened.

3.  List three examples of radioactive elements. 4.  What are some risks of studying radioactive

elements?