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Chapter 3:Chapter 3:The AtomThe Atom

and the Moleand the Mole(with nuclear)(with nuclear)

The investigation and understanding The investigation and understanding of the atom is what chemistry is all of the atom is what chemistry is all

about!about!

Topics rearranged from your text, pages 62-117.

We come here to be philosophers, and I hope you will always remember that whenever a result happens, especially if it be new, you should say, “What is the cause? Why does it occur?” and you will, in the course of time, find out the reason. -Michael Faraday

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The MoleThe Mole The “The “molemole” represents a number of ” represents a number of

thingsthings….like a dozen.….like a dozen. How many How many thingsthings is a is a molemole?? 6.022137 x 106.022137 x 102323… we use … we use 6.02 x106.02 x102323.. This is This is Avogadro’s numberAvogadro’s number

– named for a lawyer, Amadoe Avogadro, that named for a lawyer, Amadoe Avogadro, that studied molecular gasses as a hobby.studied molecular gasses as a hobby.

When you have When you have three molesthree moles of atoms, of atoms, you have (you have (33 x x 6.02x106.02x102323 =) =) 1.81x101.81x102424 atoms total.atoms total.

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Recall: Parts of the atomRecall: Parts of the atom(subatomic particles)(subatomic particles)

ProtonProton charge = +1, mass = 1 charge = +1, mass = 1 Neutron Neutron charge = 0, mass = 1 charge = 0, mass = 1 ElectronElectron charge = -1, mass = charge = -1, mass =

00 In a normal, In a normal, neutralneutral, unreacted , unreacted

atom, the atom, the number of electrons number of electrons equals the number of protonsequals the number of protons..

+10

-1

Ions have more or less electrons than protons

They have a charge

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Atomic HistoryAtomic History Greek philosopher Greek philosopher DemocritusDemocritus (400BC) (400BC)

– coined the term coined the term atomonatomon which means “that which means “that which cannot be divided.”which cannot be divided.”

John DaltonJohn Dalton (1803) a (1803) a colorblindcolorblind chemist. chemist.– Among his interests, Dalton was very Among his interests, Dalton was very

interested in a scientific explanation for his interested in a scientific explanation for his colorblindness the colorblindness the behavior of gassesbehavior of gasses..

In his In his A New System of Chemical A New System of Chemical PhilosophyPhilosophy, Dalton published , Dalton published five five principles of matterprinciples of matter..

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Dalton’s Top FiveDalton’s Top Five All matter is made of indestructible and All matter is made of indestructible and

indivisible atomsindivisible atoms..– (atoms are hard, unbreakable, the smallest thing (atoms are hard, unbreakable, the smallest thing

there is)there is) Atoms of a given element have identical Atoms of a given element have identical

physical and chemical propertiesphysical and chemical properties..– (all atoms of X will behave the same anywhere)(all atoms of X will behave the same anywhere)

Different atoms have different propertiesDifferent atoms have different properties..– (X behaves differently than Y)(X behaves differently than Y)

Atoms combine in whole-number ratios to form Atoms combine in whole-number ratios to form compoundscompounds..– (two H’s and one O = Water (H(two H’s and one O = Water (H22O)O)

Atoms cannot be divided, created or destroyed,Atoms cannot be divided, created or destroyed,– (just rearranged(just rearranged in chemical reactionsin chemical reactions).).

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The Laws:The Laws: Constant CompositionConstant Composition

– Ratios of atoms in a compound is constant for Ratios of atoms in a compound is constant for that compound.that compound.

Conservation of MassConservation of Mass– Mass is not created or destroyed in a Mass is not created or destroyed in a

chemical reaction.chemical reaction. Multiple ProportionsMultiple Proportions::

– Since atoms bond in small, whole number Since atoms bond in small, whole number ratios to form compounds, ratios to form compounds, the ratio of their the ratio of their mass ratios are small whole numbersmass ratios are small whole numbers..

Multiple Proportions.movCO

2CO

Oxygen-carbon mass ratio = 1.33

Oxygen-carbon mass ratio = 2.66

x 2

OH 2hydrogen-oxygen atomic ratio = 2:1

MultipleProportionsActivit.swf

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Conservation of Mass

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Multiple ProportionsMultiple Proportions

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The Cathode Ray TubeThe Cathode Ray Tube The The cathode ray tubecathode ray tube

– A new invention suggested the presence of A new invention suggested the presence of chargescharges – areas of positive and negative… – areas of positive and negative…charge.charge.

– This suggested that atoms must be divisible, This suggested that atoms must be divisible, and Dalton’s theory had to be modified.and Dalton’s theory had to be modified.

J. J. ThomsonJ. J. Thomson (1897) (1897)– English Physicist proposed that the atom is a English Physicist proposed that the atom is a

sphere of positive charge with small areas of sphere of positive charge with small areas of negative chargenegative charge..

– This theory become known as the “This theory become known as the “plum plum puddingpudding” model after an English “dessert” of ” model after an English “dessert” of purple bread and raisins. purple bread and raisins.

Electrostatics

Cathode-ray tube.mov

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Millikan’s OilMillikan’s Oil Thompson used electrostatics Thompson used electrostatics

experiments to determine the electron’s experiments to determine the electron’s charge-to-masscharge-to-mass ratio. ratio.

Robert Millikan’sRobert Millikan’s (1909) (1909)– oil-drop experiment allowed the charge of a oil-drop experiment allowed the charge of a

single electron to be determined: 1.60 x 10single electron to be determined: 1.60 x 10-19-19 C.C.

Scientists calculated the mass of an Scientists calculated the mass of an electron to be electron to be 1/20001/2000 of the mass of a of the mass of a proton!proton!

Millikan's Oil Drop Experiment.mov

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Ernest RutherfordErnest Rutherford Ernest Rutherford Ernest Rutherford (1910)(1910)

– New Zealander Physicist, while studying New Zealander Physicist, while studying radioactive elements, found that radioactive radioactive elements, found that radioactive alpha particles deflected when fired at a very alpha particles deflected when fired at a very thin gold foil.thin gold foil.

The The Gold Foil ExperimentGold Foil Experiment– the atom was not a hard sphere but the atom was not a hard sphere but – was was mostly spacemostly space, with a small concentration , with a small concentration

of of positively-charged masspositively-charged mass (the (the nucleusnucleus).).

Link to experimentLink to experiment

Rutherford's Goil Foil Experiment.mov

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The Bohr ModelThe Bohr Model Niels BohrNiels Bohr

– A Danish physicist (and student of A Danish physicist (and student of Rutherford) Rutherford) rebuilt the model of the atom rebuilt the model of the atom placing the electrons in placing the electrons in energy levelsenergy levels..

Bohr was one of the founders of Bohr was one of the founders of quantum quantum chemistrychemistry::– energy can be taken in and given off in energy can be taken in and given off in small small

packetspackets or or quantaquanta of of specific sizespecific size..– When a When a specific amountspecific amount of energy was added of energy was added

to an atom, an electron could jump into a to an atom, an electron could jump into a higher energy level. higher energy level.

No more…no less!

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Adding the NeutronsAdding the Neutrons James Chadwick James Chadwick (1932)(1932)

– British physicist, British physicist, proved there was too much proved there was too much mass in the nucleusmass in the nucleus

– Suggested the existence of Suggested the existence of massivemassive, , neutralneutral particles in the nucleus. particles in the nucleus. (neutrons)(neutrons)

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The Modern ModelThe Modern Model

electron

neutron

proton

(not to scale) Chadwick’s neutrons

Rutherford’s space and nucleus

Dalton’s atom

Bohr’s energy levels

Thompson’s electrons

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ElementsElements 112 known elements112 known elements

– 9292 of which are of which are naturally naturally occurringoccurring..

– 93 through 112: 93 through 112: transuraniumtransuranium.. Each has an Each has an atomic symbolatomic symbol.. Atomic numberAtomic number

– is number of is number of protonsprotons Atomic massAtomic mass

– is the total mass of the is the total mass of the protons protons plus the neutronsplus the neutrons..

OOXYGEN

8

15.9994

Notice that the atomic mass is not a round number, even though protons and neutrons each have a mass of 1. This is due to natural abundance.

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Natural Abundance - Natural Abundance - IsotopesIsotopes

Isotopes:Isotopes:– Each element may have several isotopesEach element may have several isotopes– Isotopes differ in the number of Isotopes differ in the number of neutronsneutrons..

Example:Example:– the element the element carboncarbon has 6 protons, but it has 6 protons, but it

could have 5, 6, 7, or 8 neutrons, to form could have 5, 6, 7, or 8 neutrons, to form Carbon-11, Carbon-12, Carbon-13, and Carbon-11, Carbon-12, Carbon-13, and Carbon-14.Carbon-14.

In nature, there is a In nature, there is a mix of different mix of different natural isotopesnatural isotopes..

We use this mix to calculate We use this mix to calculate average average atomic massatomic mass……

11C, 12C, 13C, 14C

IsotopesofCarbon.swf

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Calculating Calculating Average Atomic MassAverage Atomic Mass

Sum of the products = Sum of the products = average atomic average atomic massmass

Example:Example:– The isotopes of element “Bob” are found below:The isotopes of element “Bob” are found below:– Bob-18.0, 25.0%Bob-18.0, 25.0%– Bob-19.0, 60.0%Bob-19.0, 60.0%– Bob-20.0, 15.0%Bob-20.0, 15.0%– What is the average atomic mass of naturally What is the average atomic mass of naturally

occurring Bob?occurring Bob?

2015.01960.01825.0 xxx

amu9.18

1 amu = 1.66x10-27kg

(%)abundancerelative )(amumassisotope

(%)abundancerelative

(%)abundancerelative

)(amumassisotope

)(amumassisotope

:1isotope

:2isotope

:3isotope x

x

x

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Review …Review … IsotopesIsotopes– atoms of the same _______ atoms of the same _______ – different number of _______ different number of _______

IonsIons– atoms of the same _______ atoms of the same _______ – different number of _______ different number of _______

AllotropesAllotropes– forms of the same _______ forms of the same _______ – bonded in different _______ bonded in different _______

Quanta / QuantumQuanta / Quantum– Packets of energy of _______ sizePackets of energy of _______ size

Atomic MassAtomic Mass– Is the _______ of all _______ found in nature.Is the _______ of all _______ found in nature.

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Molar MassMolar Mass Molar massMolar mass

– expressed in expressed in gramsgrams per per molemole ( (g/molg/mol))– mass of one mole of a substancemass of one mole of a substance..– link between the link between the atomatom and the and the gramgram. . (we can (we can

measure)measure)

The average atomic mass of The average atomic mass of carboncarbon is is 12.0112.01. What is the mass of a mole of . What is the mass of a mole of carbon atoms?carbon atoms?

What is the molar mass of Copper, Cu?What is the molar mass of Copper, Cu?

What is the molar mass of Nitrogen, NWhat is the molar mass of Nitrogen, N22??

No more AMU:

AMU Molar mass

molgCu /5.63

molgxNx /0.2820.142

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Molar Mass PracticeMolar Mass Practice Determine the Molar Mass of the Determine the Molar Mass of the

following elements and compounds:following elements and compounds: CaCa ClCl22 CaClCaCl22 HH22OO

Ba(OH)Ba(OH)22

FeSOFeSO44

AlAl22(SO(SO44))33

molgCa /41.40

molgxClx /0.7125.352

molgxClxCa /.11125.351.402

molgxOHx /1816212 molgxxHOBa /1712)116(1372)(

molgxOxSFe /1524161.328.554

molgxxxxOxSAlx /3423)4161.32(2273)4(2

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molesmolggrams 0.5/23115

Mole-to-Mass ConversionsMole-to-Mass Conversions Sodium has an atomic mass of 23 g/mol. Sodium has an atomic mass of 23 g/mol.

How many moles do you have in 115 How many moles do you have in 115 grams?grams?

How many grams are equal to 3.5 moles How many grams are equal to 3.5 moles of CaClof CaCl22??

What is the mass of 0.46 moles of SiOWhat is the mass of 0.46 moles of SiO22??

Use a T-chart!

gramsmolgmoles 389/1115.3

27.27/1.6046. SiOgramsmolgmol

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Mole-MassMole-Mass Conversion Conversion PracticePractice Complete the following mole-to-mass conversions:Complete the following mole-to-mass conversions: Mass in grams of 2.25 moles of iron, Fe?Mass in grams of 2.25 moles of iron, Fe? 126 grams Fe126 grams Fe Mass in grams of 0.375 moles of potassium, Mass in grams of 0.375 moles of potassium,

K?K? 14.7 grams K14.7 grams K Number of moles in 5.00 grams of calcium, Number of moles in 5.00 grams of calcium,

Ca?Ca? 0.125 moles Ca0.125 moles Ca Number of moles in 3.60x10Number of moles in 3.60x10-10-10 grams of gold, grams of gold,

Au?Au? 1.83x101.83x10-12-12 mol Au mol Au

Use your periodic table to find molar mass

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Mole-Atoms Mole-Atoms ConversionsConversions MoleMole = = 6.02x106.02x102323 things things, , how many atoms how many atoms

are in:are in: 3.0 moles of silver, Ag?3.0 moles of silver, Ag? 0.010 moles of copper, Cu?0.010 moles of copper, Cu? How many moles do you have in:How many moles do you have in: 2.4x102.4x102424 atoms of helium, He? atoms of helium, He?

3.0x103.0x102323 atoms of lithium, Li? atoms of lithium, Li? How many moles do you have in 222 How many moles do you have in 222

grams of copper?grams of copper? How many atoms in 127.1 grams of How many atoms in 127.1 grams of

copper? copper?

atomsxxx 2423 108.11002.60.3

atomsx 21100.6

molesx

x0.4

1002.6

104.223

24

moles50.0

molesmolggrams 49.3/55.63/222

atomsxxmolesmolggrams 2423 1020.11002.600.2/55.63/1.127

End of Chapter 3

Phew!

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Isotopes – Isotopes – Nuclides - Nuclides - RadioactivityRadioactivity

NuclidesNuclides– the nucleus of an the nucleus of an isotopeisotope

Place the Place the massmass above the above the chargecharge as seen here. as seen here.

Nuclides undergo Nuclides undergo decaydecay: : – transformation into transformation into

different nuclidesdifferent nuclides– Balanced nuclear reactionsBalanced nuclear reactions– ““RadioactiveRadioactive””– Half Life:Half Life: time to decay ½ time to decay ½

(mass) of a sample(mass) of a sample

Images from ChemZone

mass

charge

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Alpha DecayAlpha Decay Alpha DecayAlpha Decay

– a a helium nucleushelium nucleus is is released.released.

Alpha particlesAlpha particles::– move very slowlymove very slowly– because of their size, can because of their size, can

be blocked with a few be blocked with a few pages of paper or human pages of paper or human skinskin

– cause cause ionizationionization (damaging!)(damaging!)

– are positively chargedare positively chargedImages from ChemZone

mass

charge

Alpha Decay occurs in all elements with atomic number above 83.

This is a Nuclear Equation

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Beta DecayBeta Decay Beta DecayBeta Decay

– An An electronelectron is ejected is ejected from the nucleusfrom the nucleus

Beta particlesBeta particles– move fastmove fast– can penetrate thick low-can penetrate thick low-

density materialsdensity materials– but can be but can be blocked blocked

with concrete and with concrete and metalsmetals

– are negatively chargedare negatively charged

Images from ChemZone

Beta Decay occurs when a nucleus has a high neutron-proton ratio.

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Gamma DecayGamma Decay Gamma DecayGamma Decay

– High High energy photonsenergy photons (gamma rays) are (gamma rays) are given off.given off.

Gamma raysGamma rays– given off as the “spare change” during given off as the “spare change” during

other radioactive decays….other radioactive decays….– extremely penetrating and powerful. extremely penetrating and powerful.

Several inches of Several inches of lead lead is required to slow is required to slow these particles down to a stop.these particles down to a stop.

– Don’t get included in nuclear equations.Don’t get included in nuclear equations.

Images from ChemZone

Summary of three basic particle decays

Types of radioactive decay.mov

No mass

No charge

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Nuclear Equations PracticeNuclear Equations Practice Complete the following nuclear equations:Complete the following nuclear equations:

Sodium-24Sodium-24 undergoes undergoes alpha decay alpha decay (help on click)(help on click)

Iodine-131Iodine-131 undergoes undergoes beta decaybeta decay

Tungsten-190Tungsten-190 undergoes undergoes alpha decayalpha decay

Uranium-238 undergoes alpha decay, Uranium-238 undergoes alpha decay, then two beta decays (3 steps)then two beta decays (3 steps) U-238DecaySeries.swf

FHeNa 209

42

2411

XeeI 13154

01

13153

HfHeW 18672

42

19074

ThHeU 23490

42

23892

...2411 Na ...4

22411 HeNa

PaeTh 23491

01

23490 UePa 234

9201

23491

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Nuclear FissionNuclear Fission Nuclear fission:Nuclear fission:

– splitting of large, unstable atomssplitting of large, unstable atoms– releases large amounts of energyreleases large amounts of energy

Critical massCritical mass (or critical density) (or critical density)– amount of fissionable fuel needed before amount of fissionable fuel needed before

reaction will begin.reaction will begin. Uncontrolled, nuclear fission Uncontrolled, nuclear fission

proceeds to completion with great proceeds to completion with great speed.speed.

Nuclear Weapons:Nuclear Weapons:– two half-spheres of fissionable material two half-spheres of fissionable material

are compressed together with are compressed together with conventional explosives, creating the conventional explosives, creating the critical mass.critical mass.

In order to harness nuclear fission to In order to harness nuclear fission to create useable electricity, we create useable electricity, we slow slow downdown the process with the process with control rodscontrol rods……

Once fission begins, it is difficult to stop.

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Nuclear FusionNuclear Fusion Nuclear Fusion:Nuclear Fusion:

– Joining of smaller nuclei to Joining of smaller nuclei to form larger nuclei.form larger nuclei.

– Releases Releases far more energyfar more energy that nuclear fission.that nuclear fission.

– Easier to controlEasier to control than fission than fission.. The sun’s (stars) energy comes The sun’s (stars) energy comes

from the fusion of from the fusion of hydrogenhydrogen atoms into atoms into heliumhelium atoms. atoms.

The H-bomb is a fusion weapon.The H-bomb is a fusion weapon. Fusion:Fusion:

– The power supply of the future?The power supply of the future?– Why don’t we use it now?Why don’t we use it now?

HeHH 42

21

21

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E=mcE=mc22

Einstein: Einstein: Energy and mass are Energy and mass are interchangeableinterchangeable..– E E = Energy= Energy– m m = mass= mass– c c = speed of light = speed of light ( 3 x 10( 3 x 108 8 m/s )m/s )

– Very small amounts of mass create large Very small amounts of mass create large amounts of energy!amounts of energy!

We use the formula We use the formula ΔΔE= E= ΔΔmcmc22 to build to build new, artificial elements in new, artificial elements in supercolliderssupercolliders (particle accelerators.) (particle accelerators.)

Fermilab cyclotron, Argonne National Laboratory, Chicago