Ch 4 The Structure Of The Atom Short

Chapter 4Chapter 4

Atoms and their structureAtoms and their structure

Early Theories of Matter (4.1)Early Theories of Matter (4.1) AristotleAristotle - Famous philosopher - Famous philosopher

– All substances are made of 4 All substances are made of 4 elementselements

» Fire – HotFire – Hot» Air – lightAir – light» Earth - cool, heavyEarth - cool, heavy» Water – wetWater – wet

– Blend these in different proportions to Blend these in different proportions to get all substances get all substances

Early Theories of Matter (4.1)Early Theories of Matter (4.1) DemocritusDemocritus - Famous philosopher - Famous philosopher

– Mater is composed of empty space through Mater is composed of empty space through which atoms movewhich atoms move

– Atoms are solid, homogeneous, Atoms are solid, homogeneous, indestructible, and invisible.indestructible, and invisible.

– Different atoms have different sizes and Different atoms have different sizes and shapes.shapes.

Dalton’s Atomic TheoryDalton’s Atomic Theory All All mattermatter is made of tiny is made of tiny indivisibleindivisible

particles called atoms.particles called atoms. Atoms of the same element are identical, Atoms of the same element are identical,

those of different atoms are different.those of different atoms are different. Atoms of different elements combine in Atoms of different elements combine in

whole number ratios to form compounds.whole number ratios to form compounds. Chemical reactions involve the Chemical reactions involve the

rearrangement of atoms. rearrangement of atoms. Atoms cannot be created or destroyed.Atoms cannot be created or destroyed.

Atom- The smallest particle of an Atom- The smallest particle of an element that retains the properties of element that retains the properties of the element.the element.

Subatomic Particles and the Nuclear Atom (4.2)Subatomic Particles and the Nuclear Atom (4.2)

J. J. Thomson - English physicist. 1897J. J. Thomson - English physicist. 1897 Made a piece of equipment called a Made a piece of equipment called a

cathode ray tubecathode ray tube

– It is a vacuum tube - all the air has It is a vacuum tube - all the air has been pumped out.been pumped out.

– A limited amount of other gases are A limited amount of other gases are put input in

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Metal Disks

Passing an electric current makes a beam Passing an electric current makes a beam appear to move from the negative to the appear to move from the negative to the positive endpositive end


Voltage source

+-

Voltage source


By adding an electric field By adding an electric field

+

-

Voltage source


By adding an electric field he found that the By adding an electric field he found that the moving pieces were negative moving pieces were negative

+

- By adding an electric field By adding an electric field

Thomson’s ModelThomson’s Model Found the electron.Found the electron. Electron -Electron - Negatively charged particles Negatively charged particles

of the atom.of the atom.– Mass = 9.1 x 10^-28 gramsMass = 9.1 x 10^-28 grams

Millikan’s ExperimentMillikan’s Experiment

Atomizer

Microscope

-

+

Oil

Metal Plates


Oil

Atomizer

Microscope

-

+

Oil droplets


X-rays

X-rays give some drops a charge by knocking offelectrons

-


+


They put an electric charge on the plates

++

--


Some drops would hover

++

--


+

+ + + + + + +

- - - - - - -

Some drops would hover


From the mass of the drop and the charge on the plates, he calculated the charge on an electron

++

--

Rutherford’s ExperimentRutherford’s Experiment Ernest Rutherford English physicist. Ernest Rutherford English physicist.

(1910)(1910) Used radioactivity.Used radioactivity. Alpha particles - positively charged Alpha particles - positively charged

pieces given off by uranium.pieces given off by uranium. Shot them at gold foil which can be made Shot them at gold foil which can be made

a few atoms thick.a few atoms thick.

Rutherford’s experimentRutherford’s experiment When the alpha particles hit a florescent When the alpha particles hit a florescent

screen, it glows.screen, it glows.

Here’s what it looked like (pg 95)Here’s what it looked like (pg 95)

Lead block

Uranium

Gold Foil

Fluorescent Screen

He ExpectedHe Expected The alpha particles to pass through The alpha particles to pass through

without changing direction very much.without changing direction very much. Because…Because…

– The positive charges were spread out The positive charges were spread out evenly. Alone they were not enough evenly. Alone they were not enough to stop the alpha particles.to stop the alpha particles.

What he expected

Because

Because, he thought the mass was evenly distributed in the atom

Because, he thought the mass was evenly distributed in the atom

What he got

How he explained it

+

Atom is mostly empty.Atom is mostly empty. Small dense,Small dense,

positive piecepositive piece at at center.center.

Alpha particles Alpha particles are deflected byare deflected by

it if they get close it if they get close enough. enough.

Rutherford’s experiment (cont.)Rutherford’s experiment (cont.)

+

Modern ViewModern View The atom is mostly The atom is mostly

empty space.empty space. Two regions.Two regions. NucleusNucleus- protons - protons

and neutrons.and neutrons. Electron cloud-Electron cloud-

region where you region where you might find an might find an electron.electron.

Other piecesOther pieces ProtonProton - positively charged pieces 1840 - positively charged pieces 1840

times heavier than the electron.times heavier than the electron.

NeutronNeutron - no charge but the same mass - no charge but the same mass as a proton.as a proton.

Subatomic particlesSubatomic particles

Electron

Proton

Neutron

Name Symbol ChargeRelative mass

Actual mass (g)

e-

p+

n0

-1

+1

0

1/1840

1

1

9.11 x 10-28

1.67 x 10-24

1.67 x 10-24

Structure of the AtomStructure of the Atom There are two regions.There are two regions. The The nucleusnucleus..

– With With protonsprotons and and neutronsneutrons– Positive charge.Positive charge.– Almost all the mass.Almost all the mass.

Electron cloud-Electron cloud- most of the volume of most of the volume of an atom.an atom.– The region where the electron can be The region where the electron can be

found.found.

How Atoms DifferHow Atoms Differ Atoms are small.Atoms are small.

Nucleus tiny compared to atom.Nucleus tiny compared to atom.

IF the atom was the size of a stadium, the IF the atom was the size of a stadium, the nucleus would be the size of a marble.nucleus would be the size of a marble.

Counting the PiecesCounting the Pieces Atomic Number Atomic Number = number of protons= number of protons

– # of protons determines kind of atom.# of protons determines kind of atom.

– the same as the number of electrons the same as the number of electrons in the neutral atom.in the neutral atom.

Mass Number = Mass Number = the number of protons the number of protons + neutrons.+ neutrons.

IsotopesIsotopes Dalton was wrong.Dalton was wrong. Atoms of the same element can have Atoms of the same element can have

different numbers of neutrons.different numbers of neutrons. different mass numbers.different mass numbers. Isotopes- Isotopes- Atoms with the same number Atoms with the same number

of protons but different number of of protons but different number of neutrons.neutrons.

SymbolsSymbols Contain the symbol of the element, the Contain the symbol of the element, the

mass number and the atomic number.mass number and the atomic number.

SymbolsSymbols Contain the symbol of the element, the Contain the symbol of the element, the

mass number and the atomic number.mass number and the atomic number.

X Massnumber

Atomicnumber

Naming IsotopesNaming Isotopes Put the mass number after the name of Put the mass number after the name of

the element.the element. carbon- 12carbon- 12 carbon -14carbon -14 uranium-235uranium-235

SymbolsSymbols Find the Find the

– number of protonsnumber of protons

– number of neutronsnumber of neutrons

– number of electronsnumber of electrons

– Atomic numberAtomic number

– Mass NumberMass Number

– NameName

Na2411

SymbolsSymbols Find the Find the

–number of protonsnumber of protons

–number of neutronsnumber of neutrons

–number of electronsnumber of electrons

–Atomic numberAtomic number

–Mass NumberMass Number– NameName

Br80 35

SymbolsSymbols if an element has an atomic if an element has an atomic

number of 34 and a mass number number of 34 and a mass number of 78 what is the of 78 what is the


–number of neutronsnumber of neutrons


–Complete symbolComplete symbol– NameName

SymbolsSymbols if an element has 91 protons and if an element has 91 protons and

140 neutrons what is the 140 neutrons what is the


–Mass numberMass number



SymbolsSymbols if an element has 78 electrons and if an element has 78 electrons and

117 neutrons what is the 117 neutrons what is the


–Mass numberMass number



Atomic MassAtomic Mass How heavy is an atom of oxygen?How heavy is an atom of oxygen? There are different kinds of oxygen atoms.There are different kinds of oxygen atoms. More concerned with More concerned with average average atomic mass.atomic mass. Based on abundance of each element in Based on abundance of each element in

nature.nature. Don’t use grams because the numbers Don’t use grams because the numbers

would be too small.would be too small.

Measuring Atomic MassMeasuring Atomic Mass Unit is the Unit is the Atomic Mass Unit Atomic Mass Unit (amu)(amu) One twelfth the mass of a carbon-12 One twelfth the mass of a carbon-12

atom. atom. 6 p6 p++ and 6 n and 6 n00

Each isotope has its own atomic massEach isotope has its own atomic mass we get the average using percent we get the average using percent

abundance.abundance.

Calculating averagesCalculating averages You have five rocks, four with a mass of 50 You have five rocks, four with a mass of 50

g, and one with a mass of 60 g. What is the g, and one with a mass of 60 g. What is the average mass of the rocks?average mass of the rocks?

Total mass = 4 x 50 + 1 x 60 = 260 gTotal mass = 4 x 50 + 1 x 60 = 260 g Average mass = 4 x 50 + 1 x 60 = 260 gAverage mass = 4 x 50 + 1 x 60 = 260 g

5 5 5 5 Average mass = 4 x 50 + 1 x 60 = 260 gAverage mass = 4 x 50 + 1 x 60 = 260 g

5 5 55 5 5

Calculating averagesCalculating averages Average mass = 4 x 50 + 1 x 60 = 260 gAverage mass = 4 x 50 + 1 x 60 = 260 g

5 5 5 5 5 5 Average mass = .8 x 50 + .2 x 60Average mass = .8 x 50 + .2 x 60 80% of the rocks were 50 grams80% of the rocks were 50 grams 20% of the rocks were 60 grams20% of the rocks were 60 grams Average = % as decimal x mass + Average = % as decimal x mass +

% as decimal x mass + % as decimal x mass + % as decimal x mass + % as decimal x mass +

Atomic MassAtomic Mass Calculate the atomic mass of copper if Calculate the atomic mass of copper if

copper has two isotopes. 69.1% has a mass copper has two isotopes. 69.1% has a mass of 62.93 amu and the rest has a mass of of 62.93 amu and the rest has a mass of 64.93 amu.64.93 amu.

Atomic MassAtomic Mass Magnesium has three isotopes. 78.99% Magnesium has three isotopes. 78.99%

magnesium 24 with a mass of 23.9850 magnesium 24 with a mass of 23.9850 amu, 10.00% magnesium 25 with a mass of amu, 10.00% magnesium 25 with a mass of 24.9858 amu, and the rest magnesium 25 24.9858 amu, and the rest magnesium 25 with a mass of 25.9826 amu. What is the with a mass of 25.9826 amu. What is the atomic mass of magnesium?atomic mass of magnesium?

If not told otherwise, the mass of the If not told otherwise, the mass of the isotope is the mass number in amu isotope is the mass number in amu

Atomic MassAtomic Mass Is not a whole number because it is an Is not a whole number because it is an

average. average. are the decimal numbers on the periodic are the decimal numbers on the periodic

table.table.

Unstable Nuclei and RadioactiveUnstable Nuclei and Radioactive Decay (4.4)Decay (4.4)

Up to this point the nucleus of the atom Up to this point the nucleus of the atom has remained unchangedhas remained unchanged– The protons and neutronsThe protons and neutrons

Nuclear reactionsNuclear reactions are reactions that are reactions that involve specifically changes in the involve specifically changes in the nucleus of an atom.nucleus of an atom.

Unstable Nuclei and RadioactiveUnstable Nuclei and Radioactive Decay (4.4)Decay (4.4)

Up to this point the nucleus of the atom Up to this point the nucleus of the atom has remained unchangedhas remained unchanged– The protons and neutronsThe protons and neutrons

Nuclear reactionsNuclear reactions are reactions that are reactions that involve specifically changes in the involve specifically changes in the nucleus of an atom.nucleus of an atom.

Nuclear reactions are responsible for Nuclear reactions are responsible for producing what we think of as producing what we think of as radiation.radiation.

There are three differentThere are three different forms of forms of nuclear radiationnuclear radiation– AlphaAlpha– BetaBeta– GammaGamma

Nuclear reactions are responsible for Nuclear reactions are responsible for producing what we think of as producing what we think of as radiation.radiation.

There are three differentThere are three different forms of forms of nuclear radiationnuclear radiation– AlphaAlpha– BetaBeta– GammaGamma

Particles emitted from nucleus

Spontaneous emission of radiation Spontaneous emission of radiation from an atom isfrom an atom is known asknown as radioactivityradioactivity..

Spontaneous emission of radiation Spontaneous emission of radiation from an atom isfrom an atom is known asknown as radioactivityradioactivity..

Almost all atoms we’ve encountered Almost all atoms we’ve encountered have stable nucleihave stable nuclei– Not radioactiveNot radioactive

Radioactive atoms have nuclei that are Radioactive atoms have nuclei that are disintegratingdisintegrating

So why are some nuclei stable and So why are some nuclei stable and others unstable?others unstable?

Almost all atoms we’ve encountered Almost all atoms we’ve encountered have stable nucleihave stable nuclei– Not radioactiveNot radioactive

Radioactive atoms have nuclei that are Radioactive atoms have nuclei that are disintegratingdisintegrating

So why are some nuclei stable and So why are some nuclei stable and others unstable?others unstable?

NUCLEAR STABILITYNUCLEAR STABILITY

One of the reasons is the number of One of the reasons is the number of protons and neutrons that they contain.protons and neutrons that they contain.

– Not all combinations of protons and Not all combinations of protons and neutrons are stable.neutrons are stable.

One of the reasons is the number of One of the reasons is the number of protons and neutrons that they contain.protons and neutrons that they contain.

– Not all combinations of protons and Not all combinations of protons and neutrons are stable.neutrons are stable.

The nucleus is made up of protons and The nucleus is made up of protons and neutrons densely packed together.neutrons densely packed together.

The nucleus is made up of protons and The nucleus is made up of protons and neutrons densely packed together.neutrons densely packed together.

However, protons are positiveHowever, protons are positive and the positive charges shouldand the positive charges shouldbe repelling each otherbe repelling each other

However, protons are positiveHowever, protons are positive and the positive charges shouldand the positive charges shouldbe repelling each otherbe repelling each other ++++ ++++++++

++++

++++++++

So why don’t the protons just fly apart? So why don’t the protons just fly apart? Why are most nuclei stable?Why are most nuclei stable? So why don’t the protons just fly apart? So why don’t the protons just fly apart? Why are most nuclei stable?Why are most nuclei stable?

There are 2 forces at work:

The repulsive force & a strong nuclear force.

There are 2 forces at work:

The repulsive force & a strong nuclear force.

The neutrons in the nucleus act as the The neutrons in the nucleus act as the glue that holds the nucleus together.glue that holds the nucleus together.

The neutrons in the nucleus act as the The neutrons in the nucleus act as the glue that holds the nucleus together.glue that holds the nucleus together.

A strong nuclear

force set up by the neutrons

A strong nuclear

force set up by the neutrons

All stable nuclei follow a distinct All stable nuclei follow a distinct pattern. pattern. – For elements with atomic numbers For elements with atomic numbers

between 1 and 20 stable nuclei have between 1 and 20 stable nuclei have almost equal numbers of protons almost equal numbers of protons and neutrons. Beyond 20 protons, and neutrons. Beyond 20 protons, nuclei need increasingly more nuclei need increasingly more neutrons than protons to be stable.neutrons than protons to be stable.

All stable nuclei follow a distinct All stable nuclei follow a distinct pattern. pattern. – For elements with atomic numbers For elements with atomic numbers

between 1 and 20 stable nuclei have between 1 and 20 stable nuclei have almost equal numbers of protons almost equal numbers of protons and neutrons. Beyond 20 protons, and neutrons. Beyond 20 protons, nuclei need increasingly more nuclei need increasingly more neutrons than protons to be stable.neutrons than protons to be stable.

Nuclei are unstable not only if they Nuclei are unstable not only if they contain too few neutrons, but also if contain too few neutrons, but also if they contain too many.they contain too many.

Nuclei are unstable not only if they Nuclei are unstable not only if they contain too few neutrons, but also if contain too few neutrons, but also if they contain too many.they contain too many.

Radioactive elements emit different Radioactive elements emit different kinds of radiationkinds of radiation

– Alpha Alpha – BetaBeta– GammaGamma

Each differs in charge, mass, and Each differs in charge, mass, and penetrating powerpenetrating power

Radioactive elements emit different Radioactive elements emit different kinds of radiationkinds of radiation

– Alpha Alpha – BetaBeta– GammaGamma

Each differs in charge, mass, and Each differs in charge, mass, and penetrating powerpenetrating power

Alpha radiation consists of a stream of Alpha radiation consists of a stream of high-energy alpha particleshigh-energy alpha particles

Consists of 2 protons and 2 neutrons Consists of 2 protons and 2 neutrons and is identical to a helium-4 nucleusand is identical to a helium-4 nucleus

Can be represented by the symbolCan be represented by the symbol

Alpha radiation consists of a stream of Alpha radiation consists of a stream of high-energy alpha particleshigh-energy alpha particles

Consists of 2 protons and 2 neutrons Consists of 2 protons and 2 neutrons and is identical to a helium-4 nucleusand is identical to a helium-4 nucleus

Can be represented by the symbolCan be represented by the symbol

Alpha ParticlesAlpha Particles

Alpha particles do not have much Alpha particles do not have much penetrating power.penetrating power.

They are able to travel only a few They are able to travel only a few centimeters through air and are easily centimeters through air and are easily stopped by paper or clothingstopped by paper or clothing

Not normally harmful to humansNot normally harmful to humans

Alpha particles do not have much Alpha particles do not have much penetrating power.penetrating power.

They are able to travel only a few They are able to travel only a few centimeters through air and are easily centimeters through air and are easily stopped by paper or clothingstopped by paper or clothing

Not normally harmful to humansNot normally harmful to humans

Alpha ParticlesAlpha Particles

Beta radiation consists of a stream of Beta radiation consists of a stream of high-speed electronshigh-speed electrons

A neutron changes into a proton and A neutron changes into a proton and an electronan electron– The proton remains in the nucleus The proton remains in the nucleus

and the electron is propelled out of and the electron is propelled out of the nucleusthe nucleus

Beta radiation is represented by the Beta radiation is represented by the symbolsymbol

Beta radiation consists of a stream of Beta radiation consists of a stream of high-speed electronshigh-speed electrons

A neutron changes into a proton and A neutron changes into a proton and an electronan electron– The proton remains in the nucleus The proton remains in the nucleus

and the electron is propelled out of and the electron is propelled out of the nucleusthe nucleus

Beta radiation is represented by the Beta radiation is represented by the symbolsymbol

Beta ParticlesBeta Particles

The mass number is zeroThe mass number is zero

100 times more penetrating then alpha 100 times more penetrating then alpha radiationradiation

Can damage the skinCan damage the skin

The mass number is zeroThe mass number is zero

100 times more penetrating then alpha 100 times more penetrating then alpha radiationradiation

Can damage the skinCan damage the skin

Beta ParticlesBeta Particles

A Gamma ray is highly energetic light, A Gamma ray is highly energetic light, similar to x-rayssimilar to x-rays

Does not consist of particlesDoes not consist of particles Gamma radiation accompanies alpha Gamma radiation accompanies alpha

and beta radiationand beta radiation Much more penetrating than either of Much more penetrating than either of

or or It is able to penetrate deeply into solid It is able to penetrate deeply into solid

material, including body tissuematerial, including body tissue Symbolized by: Symbolized by:

A Gamma ray is highly energetic light, A Gamma ray is highly energetic light, similar to x-rayssimilar to x-rays

Does not consist of particlesDoes not consist of particles Gamma radiation accompanies alpha Gamma radiation accompanies alpha

and beta radiationand beta radiation Much more penetrating than either of Much more penetrating than either of

or or It is able to penetrate deeply into solid It is able to penetrate deeply into solid

material, including body tissuematerial, including body tissue Symbolized by: Symbolized by:

Gamma RaysGamma Rays

Properties of Some RadiationsProperties of Some Radiations

PropertyPropertyAlphaAlpha

RadiationRadiationBeta Beta

RadiationRadiationGamma RadiationGamma Radiation

CompositionComposition Alpha ParticleAlpha Particle Beta ParticleBeta Particle High-energy photonHigh-energy photon

SymbolSymbol , He, He , e, e

ChargeCharge 2+2+ 1-1- 00

Mass (amu)Mass (amu) 44 1/18371/1837 00

4422

00-1-1

Lead, concreteLead, concreteMetal foilMetal foilPaper, clothingPaper, clothingShieldingShielding

Very highVery high(penetrates body easily)(penetrates body easily)

ModerateModerate(4mm body tissue)(4mm body tissue)

Low Low (0.05mm body (0.05mm body tissue)tissue)PowerPower

1MeV1MeV0.05 to 1 MeV0.05 to 1 MeV5 MeV5 MeVAppox.Appox.energyenergy

Cobalt-60Cobalt-60Carbon-14Carbon-14Radium-226Radium-226Common Common sourcesource

Gamma RadiationGamma RadiationBeta Beta

RadiationRadiationAlphaAlpha

RadiationRadiationPropertyProperty

Properties of Some RadiationsProperties of Some Radiations

When an atom emits one of these kinds When an atom emits one of these kinds of radiation, it is said to be decaying.of radiation, it is said to be decaying.

An atom may undergo an alpha or beta An atom may undergo an alpha or beta decay.decay.

The radiation is called decay because The radiation is called decay because the nucleus decomposes to form a new the nucleus decomposes to form a new nucleus, called transmutationnucleus, called transmutation

The best way to understand a decay is The best way to understand a decay is with a nuclear equationwith a nuclear equation

When an atom emits one of these kinds When an atom emits one of these kinds of radiation, it is said to be decaying.of radiation, it is said to be decaying.

An atom may undergo an alpha or beta An atom may undergo an alpha or beta decay.decay.

The radiation is called decay because The radiation is called decay because the nucleus decomposes to form a new the nucleus decomposes to form a new nucleus, called transmutationnucleus, called transmutation

The best way to understand a decay is The best way to understand a decay is with a nuclear equationwith a nuclear equation

Radioactive DecayRadioactive Decay

An alpha particle is a particle An alpha particle is a particle composed of 2 protons and 2 neutrons.composed of 2 protons and 2 neutrons.

With each expulsion of an alpha particle With each expulsion of an alpha particle from the atom’s nucleus the atom loses from the atom’s nucleus the atom loses 4 units of mass & 2 protons (+2 charged 4 units of mass & 2 protons (+2 charged particle)particle)

Any change in #’s of protons changes Any change in #’s of protons changes the type of atom, this is transmutation.the type of atom, this is transmutation.

An alpha particle is a particle An alpha particle is a particle composed of 2 protons and 2 neutrons.composed of 2 protons and 2 neutrons.

With each expulsion of an alpha particle With each expulsion of an alpha particle from the atom’s nucleus the atom loses from the atom’s nucleus the atom loses 4 units of mass & 2 protons (+2 charged 4 units of mass & 2 protons (+2 charged particle)particle)

Any change in #’s of protons changes Any change in #’s of protons changes the type of atom, this is transmutation.the type of atom, this is transmutation.

Alpha Decay EquationsAlpha Decay Equations

If you remember a If you remember a is an eis an e-- that is that is expelled from an atomexpelled from an atom

This electron is the result of one of the This electron is the result of one of the atom’s neutrons decomposing into a atom’s neutrons decomposing into a proton and an electron.proton and an electron.

This results in the atom having one This results in the atom having one more proton which causes it to mutate more proton which causes it to mutate into a different atom.into a different atom.

If you remember a If you remember a is an eis an e-- that is that is expelled from an atomexpelled from an atom

This electron is the result of one of the This electron is the result of one of the atom’s neutrons decomposing into a atom’s neutrons decomposing into a proton and an electron.proton and an electron.

This results in the atom having one This results in the atom having one more proton which causes it to mutate more proton which causes it to mutate into a different atom.into a different atom.

Beta Decay EquationsBeta Decay Equations

Ch 4 The Structure Of The Atom Short

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