Chapter 4 Atomic Structure Hingham High School Mr. Clune

Chapter 4Chapter 4

Atomic Structure Atomic Structure Hingham High SchoolHingham High School

Mr. CluneMr. Clune

History of the atomHistory of the atom

Not the history of atom, but the idea of Not the history of atom, but the idea of the atom.the atom.

Original idea Ancient Greece (400 Original idea Ancient Greece (400 B.C.)B.C.)

Democritus and Leucippus- Greek Democritus and Leucippus- Greek philosophersphilosophers..

Democritus’s Atomic Democritus’s Atomic TheoryTheory

Atoms are indivisible and Atoms are indivisible and indestructible.indestructible.

History of AtomHistory of Atom Looked at beachLooked at beach Made of sandMade of sand Cut sand - smaller Cut sand - smaller

sandsand

Smallest Smallest possible piece?possible piece?Atoms - not to Atoms - not to be cutbe cut

Another GreekAnother Greek

Aristotle - Famous philosopherAristotle - 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 substancesget all substances

Who’s Next?Who’s Next?

Late 1700’s - John Dalton- England.Late 1700’s - John Dalton- England. Teacher- summarized results of his Teacher- summarized results of his

experiments and those of others.experiments and those of others. Dalton’s Atomic TheoryDalton’s Atomic Theory Combined ideas of elements with that Combined ideas of elements with that

of atoms.of atoms.

John Dalton (1766-1844)John Dalton (1766-1844)

Dalton 1803Dalton 1803

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 Atoms of the same element are

identicalidentical, those of different atoms are , those of different atoms are differentdifferent..

Atoms of different elements Atoms of different elements combinecombine in in whole number ratios to form whole number ratios to form compounds.compounds.

Chemical reactions involve the Chemical reactions involve the rearrangementrearrangement of atoms. No new of atoms. No new atoms are created or destroyed.atoms are created or destroyed.

Just How Small Is an Just How Small Is an Atom?Atom?

Think of cutting a piece of Think of cutting a piece of lead into smaller and smaller lead into smaller and smaller piecespieces

How far can it be cut?How far can it be cut? An An atomatom is the smallest is the smallest

particle of an element that particle of an element that retains the properties of that retains the properties of that elementelement

HomeworkHomework

Section AssessmentSection AssessmentPage: 103Page: 103

1 – 71 – 7Due: 10/19/04Due: 10/19/04

Section 4.2Section 4.2Structure of the Nuclear AtomStructure of the Nuclear Atom

OBJECTIVES:OBJECTIVES:– Distinguish among protons, electrons, and Distinguish among protons, electrons, and

neutrons in terms of relative mass and neutrons in terms of relative mass and charge.charge.

Section 5.2Section 5.2Structure of the Nuclear AtomStructure of the Nuclear Atom

OBJECTIVES:OBJECTIVES:– Describe the structure of an atom, Describe the structure of an atom,

including the location of the protons, including the location of the protons, electrons, and neutrons with respect to electrons, and neutrons with respect to the nucleus.the nucleus.

Parts of AtomsParts of Atoms

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 tube.cathode 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.

J.J. Thompson (1856 – J.J. Thompson (1856 – 1940)1940)

Thompson 1897Thompson 1897

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Vacuum tube

Metal Disks


Voltage source

+-


Voltage source

+-


Voltage source

+-

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


Voltage source

+-



Voltage source

+-



Voltage source

+-



Voltage source

+-

Voltage source


By adding an electric fieldBy adding an electric field

Voltage source



+

-

Voltage source



+

-

Voltage source



+

-

Voltage source



+

-

Voltage source



+

-

Voltage source


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

+

-

Other particlesOther particles

Proton - positively charged pieces 1840 Proton - positively charged pieces 1840 times heavier than the electron – by E. times heavier than the electron – by E. GoldsteinGoldstein

Neutron - no charge but the same Neutron - no charge but the same mass as a proton – by J. Chadwickmass as a proton – by J. Chadwick

Where are the pieces?Where are the pieces?

Ernest Rutherford (1871-1937)Ernest Rutherford (1871-1937)

Rutherford Rutherford

Rutherford’s experimentRutherford’s experiment

Ernest Rutherford -English physicist. Ernest Rutherford -English physicist. (1910)(1910)

Believed in the plum pudding model of Believed in the plum pudding model of the atom (discussed in Chapter 13).the atom (discussed in Chapter 13).

Wanted to see how big they are.Wanted to see how big they are. Used radioactivity.Used radioactivity. Alpha particles - positively charged Alpha particles - positively charged

pieces- helium atoms minus electronspieces- helium atoms minus electrons 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 an alpha particle hits a fluorescent When an alpha particle hits a fluorescent screen, it glows.screen, it glows.

Here’s what it looked like (page 111)Here’s what it looked like (page 111)

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 thought to the positive charges were thought to

be spread out evenly. Alone they were be spread out evenly. Alone they were not enough to stop the alpha particles.not enough to stop the alpha particles.

What he expected

Because

He thought the mass was evenly distributed in the atom

Since 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 it if they get closeif they get close enough.enough.

+

Density and the AtomDensity and the Atom

Since most of the particles went Since most of the particles went through, it was mostly empty space.through, it was mostly empty space.

Because the pieces turned so much, Because the pieces turned so much, the positive pieces were heavy.the positive pieces were heavy.

Small volume, big mass, big density.Small volume, big mass, big density. This small dense positive area is the This small dense positive area is the

nucleus.nucleus.

Subatomic particles – p.106Subatomic particles – p.106

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

HomeworkHomework

Section AssessmentSection AssessmentPage: 108Page: 108

8-148-14Due: 10/20/04Due: 10/20/04

The Periodic Table: The Periodic Table: Organizing the ElementsOrganizing the Elements

OBJECTIVES:OBJECTIVES:– Identify the position of groups, periods, Identify the position of groups, periods,

and the transition metals in the periodic and the transition metals in the periodic table.table.

Counting the PiecesCounting the Pieces

Atomic Number Atomic Number = number of = number of protons in the nucleusprotons in the nucleus

# of protons determines kind of # of protons determines kind of atom (since all protons are alike!)atom (since all protons are alike!)

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

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

These account for most of massThese account for most of mass

SymbolsSymbols Contain the symbol of the Contain the symbol of the

element, the mass number element, the mass number and the atomic number.and the atomic number.

X MassNumber

AtomicNumber

Protons, Neutrons and Protons, Neutrons and ElectronsElectrons

p+ = AtomicNumber

-n0 =AtomicNumber

AtomicMass

e- = p+

Find the Find the – Mass NumberMass Number

– Atomic NumberAtomic Number

– number of protonsnumber of protons

– number of neutronsnumber of neutrons

– number of electronsnumber of electrons

F19 9

p+ = 9 e- = 9

n0= 19 - 9=10

Find the Find the

–Mass NumberMass Number

–Atomic numberAtomic number

–number of protonsnumber of protons

–number of neutronsnumber of neutrons

–number of electronsnumber of electrons

Br80 35

p+ = 35 e- = 35n0= 80 – 35 = 45

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

p+ = 34 n0 = 78 – 34 = 44

e- = 34

Se

if an element has 91 protons if an element has 91 protons and 140 neutrons what is the and 140 neutrons what is the


–Mass numberMass number



At # = 91Mass # = 91+140

231

e- = 91

Pr

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



At # = 78Mass # =78+117

195

p+ = 78

Pt

IsotopesIsotopes

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

different numbers of different numbers of neutronsneutrons.. different mass numbers.different mass numbers. called called isotopes.isotopes.

IsotopesAtoms of the same element with

different number of neutrons.

1P+2N

1e-

Tritium

Average Atomic Mass for H = 1.00794

1P+1N

1e-

Deuterium

1P+0N

1e-

Protium

Naming IsotopesNaming Isotopes

We can also put the mass number after We can also put the mass number after the name of the element.the name of the element.

carbon- 12carbon- 12 carbon -14carbon -14 uranium-235uranium-235

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 atomic mass.mass.

Based on abundance of each element Based on abundance of each element in nature.in 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. Each isotope has its own atomic mass, Each isotope has its own atomic mass,

thus we determine the average from thus we determine the average from percent abundance.percent abundance.

Calculating averagesCalculating averages

Multiply the atomic mass of Multiply the atomic mass of each isotope by it’s abundance each isotope by it’s abundance (expressed as a decimal), then (expressed as a decimal), then add the results.add the results.

Sample Problem – Page 117Sample Problem – Page 117

Atomic Mass #23Atomic Mass #23

Calculate the atomic mass of Calculate the atomic mass of copper if copper has two copper if copper has two

isotopes. 69.2% has a mass isotopes. 69.2% has a mass of 62.93 amu and the rest of 62.93 amu and the rest has a mass of 64.93 amu.has a mass of 64.93 amu.


69.2% of 62.93 amu 69.2% of 62.93 amu

(100% - 69.2%) of 64.93 amu(100% - 69.2%) of 64.93 amu

.692 X 62.93 amu = 43.55 amu .692 X 62.93 amu = 43.55 amu

.308 X 64.93 amu = 20.00 amu.308 X 64.93 amu = 20.00 amu++

63.55 amu 63.55 amu


Calculate the atomic mass of Calculate the atomic mass of bromine. The two isotopes of bromine. The two isotopes of bromine have atomic masses bromine have atomic masses

and relative abundance of and relative abundance of

78.92 amu (50.69%) 78.92 amu (50.69%) and and

80.92 amu (49.31%).80.92 amu (49.31%).


50.69% of 78.92 amu 50.69% of 78.92 amu

49.31% of 80.92 amu49.31% of 80.92 amu

.5069 X 78.92 amu = 40.00 amu .5069 X 78.92 amu = 40.00 amu

.4931 X 80.92 amu = 39.90 amu.4931 X 80.92 amu = 39.90 amu++

79.90 amu 79.90 amu


Magnesium has three isotopes. Magnesium has three isotopes. 78.99% magnesium 24 with a mass of 78.99% magnesium 24 with a mass of 23.9850 amu, 10.00% magnesium 25 23.9850 amu, 10.00% magnesium 25 with a mass of 24.9858 amu, and the with a mass of 24.9858 amu, and the rest magnesium 25 with a mass of rest magnesium 25 with a mass of 25.9826 amu. What is the atomic mass 25.9826 amu. What is the atomic mass of magnesium?of magnesium?

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


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 are the decimal numbers on the periodic table.periodic table.

Development of the Periodic Development of the Periodic TableTable

mid-1800s, about 70 elementsmid-1800s, about 70 elements Dmitri Dmitri MendeleevMendeleev – Russian chemist – Russian chemist Arranged elements in order of Arranged elements in order of

increasing atomic massincreasing atomic mass Thus, the first “Periodic Table” Thus, the first “Periodic Table”

Dimitri MendeleevDimitri Mendeleev

Mendeleev Periodic TableMendeleev Periodic Table

MendeleevMendeleev

Left blanks for undiscovered elementsLeft blanks for undiscovered elements When discovered, good predictionWhen discovered, good prediction Problems?Problems?

– Co and Ni; Ar and K; Te and ICo and Ni; Ar and K; Te and I

New wayNew way

Henry Henry MoseleyMoseley – British physicist – British physicist Arranged elements according to Arranged elements according to

increasing increasing atomic numberatomic number The arrangement todayThe arrangement today Symbol, atomic number & massSymbol, atomic number & mass

Henry MoseleyHenry Moseley

http://www.google.com/imgres?imgurl=http://geocities.yahoo.com.br/chemicalnet/moseley.jpg&imgrefurl=http://geocities.yahoo.com.br/chemicalnet/ht_txt5.html&h=200&w=142&sz=9&tbnid=jGQO0jGRilYJ:&tbnh=98&tbnw=70&start=9&prev=/images%3Fq%3DHenry%2BMoseley%26svnum%3D10%26hl%3Den%26lr%3D

Periodic tablePeriodic table

Horizontal rows = Horizontal rows = periodsperiods– There are 7 periodsThere are 7 periods

Periodic law:Periodic law: Vertical column = Vertical column = groupgroup (or family) (or family)

– Similar physical & chemical prop.Similar physical & chemical prop.

– Identified by number & letterIdentified by number & letter

Areas of the periodic tableAreas of the periodic table

Group A elements = Group A elements = representative representative elementselements– Wide range of phys & chem prop.Wide range of phys & chem prop.

– MetalsMetals: electrical conductors, have luster, : electrical conductors, have luster, ductile, malleableductile, malleable

Groups of ElementsGroups of Elements

The vertical columns in the Periodic Table. Elements in

each group have similar properties.

Groups of ElementsGroups of Elements

Example: Group 11

CopperSilverGold

MetalsMetals

Group IA – Group IA – alkali metalsalkali metals Group 2A – Group 2A – alkaline earth metalsalkaline earth metals Transition metalsTransition metals and and InnerInner transition transition

metalsmetals – Group B – Group B All metals are solids at room All metals are solids at room

temperature, except _____.temperature, except _____.

NonmetalsNonmetals

NonmetalsNonmetals: generally nonlustrous, : generally nonlustrous, poor conductors of electricitypoor conductors of electricity– Some gases (O, N, Cl); some are Some gases (O, N, Cl); some are

brittle solids (S); one is a fuming dark brittle solids (S); one is a fuming dark red liquid (Br)red liquid (Br)

Group 7A – Group 7A – halogenshalogens Group 0 – Group 0 – noble gasesnoble gases

Division between metal & Division between metal & nonmetalnonmetal

Heavy, stair-step lineHeavy, stair-step line MetalloidsMetalloids border the line border the line

– Properties intermediate between Properties intermediate between metals and nonmetalsmetals and nonmetals

Learn the general behavior and Learn the general behavior and trends of the elements, instead of trends of the elements, instead of memorizing each element property memorizing each element property

MetalsTransitionElements

Non-Metals

Metalloids

Halogens

Noble Gases

Alkali M

etalsA

lkaline Earth M

etals

HomeworkHomeworkReview SheetsReview Sheets

4.1 and 4.24.1 and 4.2Due: 10/27/04Due: 10/27/04

4.314.31Due: 10/28/04Due: 10/28/04Test: 10/29/04Test: 10/29/04

Dc102

50

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Chapter 4 Atomic Structure Hingham High School Mr. Clune