Copyright© by Houghton Mifflin Copyright© by Houghton Mifflin Company. All rights reserved.Company. All rights reserved.

Atomic Atomic StructureStructure

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Composition of the AtomComposition of the Atom

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An atom An atom viewed viewed in cross in cross section.section.

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It takes 190,000,000 copper It takes 190,000,000 copper atoms to span the diameter of atoms to span the diameter of

a penny!!!!!a penny!!!!!

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Is it possible that there is no Is it possible that there is no God?God?

Consider the following logic:Consider the following logic:

The universe had a beginningThe universe had a beginning

All things that begin need a beginnerAll things that begin need a beginner

Therefore, the universe had a beginnerTherefore, the universe had a beginner

It is inescapable that something It is inescapable that something

created the universe!created the universe! We call that something “God”We call that something “God” Given what we know about the universe, Given what we know about the universe,

God is immensely powerful!God is immensely powerful!

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AtomAtom Smallest particle of an element that Smallest particle of an element that

retains the chemical identity of the retains the chemical identity of the elementelement

Remember: elements are pure substancesRemember: elements are pure substances

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Atomic Atomic MicroscopyMicroscopy

Scanning Electron Scanning Electron

Microscope--SEMMicroscope--SEM

Gold Atomic

Structure

5nm

Silicon Atoms

Atomic Diameter= 0.234nm

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Dalton’s Atomic Theory of Dalton’s Atomic Theory of MatterMatter

Each element composed of tiny particles called Each element composed of tiny particles called atomsatoms

All atoms of a given element are identical—but All atoms of a given element are identical—but different from all othersdifferent from all others

Atoms cannot be subdivided, created, or Atoms cannot be subdivided, created, or destroyed in chemical reactionsdestroyed in chemical reactions

Atoms of different elements combine in simple Atoms of different elements combine in simple whole number ratios to form compoundswhole number ratios to form compounds

In chemical reactions, atoms are combined, In chemical reactions, atoms are combined, separated, or rearranged.separated, or rearranged.

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Greeks Through the 1700’sGreeks Through the 1700’sDemocritus 450 BCDemocritus 450 BC All matter composed of “atomos”All matter composed of “atomos” Aristotle disagreed:Aristotle disagreed:

What holds these atomos together?What holds these atomos together?

LavoisierLavoisier Law of Conservation of MatterLaw of Conservation of Matter

ProustProust Law of constant compositionLaw of constant composition

Compounds have same proportions by massCompounds have same proportions by mass

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Discovering Atomic StructureDiscovering Atomic Structure Franklin—1706-1790Franklin—1706-1790

Kite in a thunderstorm storyKite in a thunderstorm story Concluded that objects have two kinds of charge: + Concluded that objects have two kinds of charge: +

- - (like repel)(like repel) Lightning is static electricity on a large scaleLightning is static electricity on a large scale Where do charges come from?Where do charges come from?

Faraday—1839 Faraday—1839 Atomic structure related to electricityAtomic structure related to electricity Electricity comes from Greek “elektron”Electricity comes from Greek “elektron” After many experiments—Atoms contain particles After many experiments—Atoms contain particles

that have electric chargethat have electric charge

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Sub Atomic ParticlesSub Atomic Particles Much of Dalton’s theory is still accepted Much of Dalton’s theory is still accepted

todaytoday Exception:Exception:

Atoms are divisible into subatomic particlesAtoms are divisible into subatomic particles ProtonsProtons NeutronsNeutrons ElectronsElectrons

In 1897 English physicist J. J. Thompson In 1897 English physicist J. J. Thompson discovered the electrondiscovered the electron Electrons are negatively charged particles.Electrons are negatively charged particles.

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Cathode Ray TubeCathode Ray Tube

Thompson used the CRT to investigate electrons

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Thompson modified the Thompson modified the CRT as shown belowCRT as shown below

A paddle wheel was placed in the stream of electrons. The electron beam made the wheel spin leading to the conclusion that electrons have mass.

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J. J. Thompson (1856-1940)J. J. Thompson (1856-1940)

In 1896 . . .In 1896 . . . Thompson modified the CRTThompson modified the CRT Concluded: cathode ray composed of Concluded: cathode ray composed of

negatively charged particlesnegatively charged particles 1.76 x 10 1.76 x 10 88 Coulombs/gram Coulombs/gram

Thompson concluded that negative particles Thompson concluded that negative particles issued from the cathodeissued from the cathode

Meant that atoms have a substructureMeant that atoms have a substructure If there were negative parts of the atom, then If there were negative parts of the atom, then

there must be positive parts of the atom because there must be positive parts of the atom because atoms are normally neutralatoms are normally neutral

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Mass of an ElectronMass of an Electron Thompson was not able to determine charge of Thompson was not able to determine charge of

single electronsingle electron Millikan’s oil drop experiment did thatMillikan’s oil drop experiment did that Milikan determinedMilikan determined

Charge of electron = 1.60 x 10Charge of electron = 1.60 x 10-19 -19 coulombscoulombs Mass of electron = 9.11 x 10Mass of electron = 9.11 x 10-28-28 grams grams

Mass of electron = 9.109 x 10Mass of electron = 9.109 x 10-31-31kgkg 1/20001/2000thth the mass of a hydrogen atom the mass of a hydrogen atom

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Thompson Plum Pudding Thompson Plum Pudding model of an atom.model of an atom.

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Properties of Subatomic Properties of Subatomic ParticlesParticles

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Rutherford’s experiment circa Rutherford’s experiment circa 19091909

(alpha scattering experiment)(alpha scattering experiment)

1/8000 alpha particle were deflectedLike a Toyota hitting a Mack truck!!Rutherford had discovered the nucleus

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Alpha particles scattered Alpha particles scattered from the gold foilfrom the gold foil

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Result of Rutherford Gold Foil Result of Rutherford Gold Foil ExperimentExperiment

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Results of foil experiment if Results of foil experiment if Plum Pudding model had Plum Pudding model had

been correct.been correct.

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Atomic NumberAtomic Number4.3

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Modern Atomic TheoryModern Atomic Theory Atoms composed of protons, neutrons and electrons.Atoms composed of protons, neutrons and electrons.

Protons and neutrons form the nucleusProtons and neutrons form the nucleus Electrons move in the space outside the nucleusElectrons move in the space outside the nucleus

Atomic number = number of protonsAtomic number = number of protons Ions are atoms with a chargeIons are atoms with a charge

Ionic charge = #protons - #electronsIonic charge = #protons - #electrons Isotopes are atoms with the same number of protons Isotopes are atoms with the same number of protons

but different number of neutronsbut different number of neutrons Hydrogen-1Hydrogen-1 protiumprotium Hydrogen-2 Hydrogen-2 deuteriumdeuterium Hydrogen-3Hydrogen-3 TritiumTritium

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Figure 3.10: Two isotopes of Figure 3.10: Two isotopes of sodium.sodium.

Mass #

SymbolAtomic # Mass # = Atomic # + # neutrons

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IsotopesIsotopes

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Chemical SymbolsChemical Symbols

27 3+27 3+ 79 2-79 2-

AlAl Se Se

1313 3434

#protons = ?#protons = ?

#neutrons = ?#neutrons = ?

# electrons = ?# electrons = ?

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Atomic Atomic MassMass

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Atomic MassAtomic Mass

The The atomic massatomic mass of an element is a weighted of an element is a weighted average mass of the atoms in a naturally average mass of the atoms in a naturally occurring sample of the element.occurring sample of the element.A weighted average mass reflects both the A weighted average mass reflects both the mass and the relative abundance of the mass and the relative abundance of the isotopes as they occur in nature.isotopes as they occur in nature.

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Atomic MassAtomic Mass

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AMUAMU

1/12 mass of a carbon atom = 1.66 x 101/12 mass of a carbon atom = 1.66 x 10-24-24g =1amug =1amu Chlorine-35Chlorine-35 34.969 AMU34.969 AMU

Atomic massAtomic mass on periodic table is really average atomic on periodic table is really average atomic mass in AMU’smass in AMU’sFor ChlorineFor Chlorine

Atomic Mass =.7577 x 34.969 + .2223 x 36.966 = 35.453Atomic Mass =.7577 x 34.969 + .2223 x 36.966 = 35.453 Chlorine 35 Chlorine 37Chlorine 35 Chlorine 37

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Periodic TablePeriodic Table

A periodic table is an arrangement of elements in Which the elements are separated into groups based on a set of repeating properties.

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Nuclear StabilityNuclear Stability Nucleus held together by strong nuclear forcesNucleus held together by strong nuclear forces

Occur for objects very close togetherOccur for objects very close together Neutrons are glueNeutrons are glue

Provide SNF without repulsionProvide SNF without repulsion

+ + nn

+

nn +

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Belt of StabilityBelt of Stability

# protons (atomic #)

#neutrons

More than one neutrons for every

proton

One proton for every neutron

Atomic # = 20

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Radioactive Particles

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Radioactive ParticlesRadioactive Particles

Ernest Rutherford (1871-1937)Ernest Rutherford (1871-1937) In early 1900’s experimented with radioactive materialsIn early 1900’s experimented with radioactive materials

ChargeCharge NameName Penetrating Ability Penetrating Ability

-particle-particle 2+2+ alpha stopped by paperalpha stopped by paper

-particle-particle 1-1- betabeta stopped by foil/clothes stopped by foil/clothes

-ray-ray nonenone gamma stopped by leadgamma stopped by lead

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Radioactive ParticlesRadioactive Particles

CompositionComposition

-particle-particle helium nuclei (2 protons & 2 Neutrons)helium nuclei (2 protons & 2 Neutrons)

-particle-particle electronelectron

-ray -ray high energy radiationhigh energy radiation

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Radioactive DecayRadioactive Decay

Alpha Decay

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FusionFusion

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The Positively Charged The Positively Charged NucleusNucleus

Henry Mosely (1887-1915)Henry Mosely (1887-1915) Every element contains a unique positive charge in its Every element contains a unique positive charge in its

nucleusnucleus

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The Periodic Table.The Periodic Table.

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The ions formed by selected The ions formed by selected members of groups 1, 2, 3, 6, members of groups 1, 2, 3, 6,

and 7.and 7.Ionic Charge = Atomic Number - # electrons

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Top TenTop Ten

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Top Ten Top Ten

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Antares is the 15th brightest star in the sky.

It is more than 1000 light years away!