Chapter 5Chapter 5

“Atomic Structure”“Atomic Structure”

ChemistryChemistryOlympic High SchoolOlympic High School

Mr. DanielMr. Daniel

Credits: Stephen L. Cotton Credits: Stephen L. Cotton

Charles Page High SchoolCharles Page High School

Section 5.1 Defining the AtomSection 5.1 Defining the Atom

OBJECTIVES:OBJECTIVES: DescribeDescribe the history of the development of the history of the development of

ideas about atoms.ideas about atoms.

ExplainExplain Dalton’s atomic theory. Dalton’s atomic theory.

Describe the size of the atom.Describe the size of the atom.

Section 5.1 Defining the AtomSection 5.1 Defining the Atom

The Greek philosopherThe Greek philosopher DemocritusDemocritus (460 B.C. – 370 B.C.)(460 B.C. – 370 B.C.) was among the was among the first to suggest the existence of atomsfirst to suggest the existence of atoms ((from the Greek word “atomos” – from the Greek word “atomos” – meaning “unable to be cut”)meaning “unable to be cut”)

Antoine Laurent Antoine Laurent Lavoisier (1743-1794)Lavoisier (1743-1794)

The Father of Modern The Father of Modern Chemistry: discovered Chemistry: discovered oxygen & hydrogenoxygen & hydrogen,, developed modern developed modern thermodynamics, thermodynamics,

invented the first periodic invented the first periodic tabletable

Dalton’s Atomic TheoryDalton’s Atomic Theory (experiment based) (experiment based)

3) Atoms of different elements combine in simple whole-number ratios to form chemical compounds

4) In chemical reactions, atoms are combined, separated, or rearranged – but never changed into atoms of another element.

1) All elements are composed of tiny indivisible particles called atoms

2) Atoms of the same element are identical. Atoms of any one element are different from those of any other element. John Dalton

(1766 – 1844)

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

OBJECTIVES:OBJECTIVES: IdentifyIdentify three types of subatomic particles and three types of subatomic particles and

their properties.their properties. DescribeDescribe the structure of atoms, according to the structure of atoms, according to

the Rutherford Model.the Rutherford Model.

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

One change to Dalton’s atomic theory is that atoms One change to Dalton’s atomic theory is that atoms are divisibleare divisible into subatomic particles: into subatomic particles: Electrons, protons, and neutrons are examplesElectrons, protons, and neutrons are examples of of

these fundamental particlesthese fundamental particles There are many other types of particles, but we There are many other types of particles, but we

will study these threewill study these three

In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively

charged particle: the electron

The electron’s charge-to-mass ratio = 1.76 The electron’s charge-to-mass ratio = 1.76 10 1088 C/g C/g

JJ Thomsonl

CCathode athode RRay ay TTubes ubes

Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

A CRT from a Radar Scope (WW II)

A Standard

Television Tube (First common in the 1950’s)

Standard Computer Monitor (often called a “CRT”)

Mass of the ElectronMass of the Electron

1916 – Robert Millikan determined the mass of the electron: 1/1840 the mass of a hydrogen atom; has one unit of negative charge

The oil drop apparatus

Mass of the electron is 9.11 x 10-28 g

simulation

Robert Millikan

Conclusions from the Study of the ElectronConclusions from the Study of the Electron::

a) Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons.

b) Atoms are neutral, so there must also be positive particles in the atom to balance the negative charge of the electrons

c) Electrons have very little mass, therefore atoms must contain other particles that account for most of the mass

Thomson’s Atomic ModelThomson’s Atomic Model

Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

J. J. Thomson

Other Particle Discoveries:Other Particle Discoveries:

Eugen Goldstein first observed evidence of what is now called the “proton” in 1886 - particles with a positive charge, and a mass of 1840 times that of an electron. It’s existance was later confirmed by Ernest Rutherford in 1919.

1932 – James Chadwick confirmed the existence of the “neutron” – a particle with no charge, but a mass nearly equal to a proton

The problem:The problem:In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target?

Target #1 The Answer:The Answer:

The AnswerThe AnswerTarget #2

Ernest Rutherford’sErnest Rutherford’sGold Foil Experiment - 1911Gold Foil Experiment - 1911

Alpha particles are helium nuclei - The alpha particles were fired at a thin sheet of gold foil

Particle that hit on the detecting screen (film) are recorded

Rutherford’s FindingsRutherford’s Findings

a) The nucleus is smallb) The nucleus is densec) The nucleus is positively

charged

Most of the particles passed right through A few particles were deflected VERY FEW were greatly deflected

“Like howitzer shells bouncing off of tissue paper!”

Conclusions:

The Rutherford Atomic ModelThe Rutherford Atomic ModelBased on his experimental evidence, Based on his experimental evidence, Rutherford’s Rutherford’s Nuclear ModelNuclear Model was developed and stated: was developed and stated:

The atom is mostly empty spaceThe atom is mostly empty space

The electrons are distributed around the nucleus, and The electrons are distributed around the nucleus, and occupy most of the volumeoccupy most of the volume

Because of the exceptionally high mass of the Because of the exceptionally high mass of the nucleus, it must contain particles in addition to nucleus, it must contain particles in addition to protons (neutrons were discovered later)protons (neutrons were discovered later)

All the positive charge, and almost All the positive charge, and almost all the mass is concentrated in a all the mass is concentrated in a small area in the center. He called small area in the center. He called this a “this a “nucleusnucleus””

Ernest Rutherford video

Subatomic ParticlesSubatomic Particles

ParticleParticle ChargeCharge Mass (g)Mass (g) LocationLocation

Electron Electron -1 -1 9.11 x 10 9.11 x 10-28-28 Electron Electron (e(e--)) cloud cloud

ProtonProton +1 +1 1.67 x 10 1.67 x 10-24-24 Nucleus Nucleus (p(p++)) (1 atomic mass unit)(1 atomic mass unit)

Neutron Neutron 0 0 1.67 x 101.67 x 10-24-24 NucleusNucleus (n(noo)) (1 atomic mass unit)(1 atomic mass unit)

Crash Course Chemistry - History of Chemical Concepts

Sizing up the AtomSizing up the Atom Elements can be subdivided into smaller and smaller pieces until there are only single atoms; The smallest particles of an element that still have the properties of that element.

100,000,000 copper atoms in a single file, would be approximately 1 cm longDespite their incredibly small size, individual atoms have recently become observable with scanning tunneling microscopes

Image: Fe atoms on a Cu surfaceImage: Fe atoms on a Cu surfaceForming a Image: Fe atoms on a Cu surfaceForming a Image: Fe atoms on a Cu surfaceImage: Fe atoms on a Cu surfaceImage: Fe atoms on a Cu surface

The Beginning: Xe on NiAtomic Kanji“original child”Carbon Monoxide ManAn Artistic View of Ni

Section 5.3Section 5.3Distinguishing Among AtomsDistinguishing Among Atoms

OBJECTIVES:OBJECTIVES: ExplainExplain what makes isotopes different from what makes isotopes different from

each other.each other.CalculateCalculate the number of protons, neutrons the number of protons, neutrons and electrons in an atom using atomic and electrons in an atom using atomic number and massnumber and mass

CalculateCalculate the average atomic mass and the average atomic mass and atomic number.atomic number.

Atomic NumberAtomic Number

Atoms are composed of protons, neutrons, and electronsAtoms are composed of protons, neutrons, and electrons How then are atoms of one element different from How then are atoms of one element different from

another element?another element?

Elements are different because they contain different Elements are different because they contain different numbers of numbers of PROTONSPROTONS

Atomic number (Z) : the number of protons in the nucleus of each atom of that element.

An atom is always neutral, therefore:An atom is always neutral, therefore:

# protons in an atom = # electrons# protons in an atom = # electrons

ElementElement # of # of protonsprotons

# of # of electronselectrons

Atomic # Atomic # (Z)(Z)

CarbonCarbon 66 66 66

PhosphorusPhosphorus 1515 1515 1515

IodineIodine 5353 5353 5353

GoldGold 7979 7979 7979

Mass NumberMass Number

Mass number is the number of protons and neutrons in the nucleus of an atom:

Mass # = p+ + n0

NuclideNuclide pp++ nn00 ee-- Mass #Mass #

Oxygen Oxygen - - 1010

- - 3333 4242

- - 3131 1515

8 8 1818

Arsenic 75 33 75

Phosphorus 15 3116

Complete SymbolsComplete Symbols contain the symbol of the contain the symbol of the element, the mass number and the atomic element, the mass number and the atomic number.number.

X Massnumber

AtomicnumberSubscript →

Superscript →

Examples:

C

C

U

12

6

6

14

92

235

Complete SymbolsComplete Symbols

Symbols continued…Symbols continued…

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

SymbolsSymbols

Find each of these: Find each of these:

a)a) number of protonsnumber of protons

b)b) number of neutronsnumber of neutrons

c)c) number of electronsnumber of electrons

d)d) Atomic numberAtomic number

e)e) Mass NumberMass Number

Br80

35

a) 35b) 45c) 35d) 35e) 80

SymbolsSymbols

If an element has an atomic number of 34 If an element has an atomic number of 34 and a mass number of 78, what is the: and a mass number of 78, what is the:

a)a) number of protonsnumber of protons

b)b) number of neutronsnumber of neutrons

c)c) number of electronsnumber of electrons

d)d) complete symbolcomplete symbol

a) 34b) 44c) 34d) Se

34

78

SymbolsSymbols If an element has 91 protons and 140 If an element has 91 protons and 140

neutrons what is the neutrons what is the

a)a) Atomic numberAtomic number

b)b) Mass numberMass number

c)c) number of electronsnumber of electrons

d)d) complete symbolcomplete symbol

a) 91b) 231c) 91d) Pa

231

91

SymbolsSymbols If an element has 78 electrons and 117 If an element has 78 electrons and 117

neutrons what is the neutrons what is the

a)a) Atomic numberAtomic number

b)b) Mass numberMass number

c)c) number of protonsnumber of protons

d)d) complete symbolcomplete symbol

a) 78b) 195c) 78d) Pt 78

195

IsotopesIsotopes

Dalton was wrong about all elements of the same Dalton was wrong about all elements of the same type being identical:type being identical:

Atoms of the same element Atoms of the same element cancan have different have different numbers of numbers of neutronsneutrons..Thus, they have different mass numbers.Thus, they have different mass numbers.These are called These are called isotopesisotopes..

Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons.

IsotopeIsotope ProtonsProtons ElectronsElectrons NeutronsNeutrons NucleusNucleus

Hydrogen–1Hydrogen–1

(protium)(protium) 11 11 00

Hydrogen-2Hydrogen-2

(deuterium)(deuterium) 11 11 11

Hydrogen-3Hydrogen-3

(tritium)(tritium)

11 11 22

IsotopesIsotopesElements occur in nature as mixtures of isotopes.

Atomic MassAtomic Mass How heavy is an atom of oxygen?How heavy is an atom of oxygen?

It depends, because there are different It depends, because there are different kindskinds of of oxygen atoms.oxygen atoms.

We generally refer to the We generally refer to the average average atomic mass.atomic mass.

Average atomic massAverage atomic mass is based on the abundance is based on the abundance (percentage) of each isotope of an element as it is (percentage) of each isotope of an element as it is found in naturefound in nature.. It is the number (red) that we find on the periodic It is the number (red) that we find on the periodic

tabletable

Measuring Atomic MassMeasuring Atomic Mass Instead of grams, the mass unit we use for atoms Instead of grams, the mass unit we use for atoms

is the is the Atomic Mass UnitAtomic Mass Unit (amu or (amu or µµ)) It is defined as one-twelfth the mass of a carbon-12 It is defined as one-twelfth the mass of a carbon-12

atom.atom.

Carbon-12 is chosen because of its isotope purity.Carbon-12 is chosen because of its isotope purity.

Each isotope has its own atomic mass, thus we Each isotope has its own atomic mass, thus we determine the average mass from the percent determine the average mass from the percent

abundance of each isotope.abundance of each isotope.

Atomic MassesAtomic Masses

IsotopeIsotope SymbolSymbol Composition of Composition of the nucleusthe nucleus

% in nature% in nature

Carbon-12Carbon-12 1212CC 6 protons6 protons

6 neutrons6 neutrons

98.89%98.89%

Carbon-13Carbon-13 1313CC 6 protons6 protons

7 neutrons7 neutrons

1.11%1.11%

Carbon-14Carbon-14 1414CC 6 protons6 protons

8 neutrons8 neutrons

<0.01%<0.01%

Atomic mass is the average of all the naturally occurring isotopes of that element.

Carbon = 12.0107 µ

To To calculatecalculate the average atomic mass: the average atomic mass:

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

The mass of the isotope The mass of the isotope is expressed in is expressed in atomic atomic mass unitsmass units (amu (amu oror µ)µ)

Isotope Symbol % in nature

Carbon-12 12C 98.89%

(12.00 µ) (.9889) + 12.01 µ

Carbon-13 13C 1.11%

Carbon-14 Carbon-14 1414CC <0.01%<0.01%

(13.00 µ) (.0111) =

Atomic Mass CalculationAtomic Mass CalculationElement X has two natural isotopes. The isotope with a mass of 10.012 amu has a relative abundance of 19.91%. The isotope with a mass of 11.009 amu has a relative abundance of 80.09%. Calculate the atomic mass of this element.

(10.012 µ) (.1991) + (11.009 µ) (.8009) =

10.81 µBoron

Section 5.4Section 5.4Organizing the ElementsOrganizing the Elements

OBJECTIVES:OBJECTIVES: ExplainExplain how elements are organized in a how elements are organized in a

periodic table.periodic table.CompareCompare early and modern periodic tables. early and modern periodic tables.

IdentifyIdentify three broad classes of elements. three broad classes of elements.

DistinguishDistinguish different areas of different areas of the periodic table.the periodic table.

Section 5.4Section 5.4Organizing the ElementsOrganizing the Elements

A few elements, such as gold and copper, have been known for thousands of years.

Yet, only about 13 (of 90) had been identified by the year 1700.

As more were discovered, chemists realized they needed a way to organize the elements.

Section 5.4Section 5.4Organizing the ElementsOrganizing the Elements

Chemists used the Chemists used the propertiesproperties of elements of elements to sort them into groups.to sort them into groups.

In 1829 J. W. Dobereiner arranged In 1829 J. W. Dobereiner arranged elements into elements into triadstriads – groups of three – groups of three elements with similar propertieselements with similar properties

        (40 + 137) ÷ 2 = 88(40 + 137) ÷ 2 = 88

Ca 40Sr 88Ba 137

Li 7Na 23K 39

Cl 35Br 80I 127

John Newlands John Newlands (1837-1898)(1837-1898) Law of Octaves:Law of Octaves: noted that after interval of noted that after interval of

eight elements, similar physical/chemical eight elements, similar physical/chemical properties reappearedproperties reappeared.  . 

Newlands was the first to formulate the concept Newlands was the first to formulate the concept of of periodicityperiodicity (repeating patterns) (repeating patterns) in the in the properties of the chemical elements.properties of the chemical elements.

Mendeleev’s Periodic TableMendeleev’s Periodic Table

Dmitri Dmitri MendeleevMendeleev – A Russian – A Russian chemist arranged the elements in chemist arranged the elements in order of increasing order of increasing atomic massatomic mass

It was the beginning of the modern It was the beginning of the modern “Periodic Table” “Periodic Table”

By the mid-1800s, about By the mid-1800s, about 70 elements were known to 70 elements were known to existexist

Lothar Meyer

Mendeleev left blanks for elements he Mendeleev left blanks for elements he predicted that existed such as predicted that existed such as GermaniumGermaniumWhen discovered, the elements When discovered, the elements generally matched his predictionsgenerally matched his predictionsBut, there were problems: some But, there were problems: some elements did not fit with their groupselements did not fit with their groups

Co and Co and Ni; Ar Ni; Ar and K; and K; Te and ITe and I

His Original Table…His Completed Work…

A better arrangement…A better arrangement… In 1913, Henry In 1913, Henry MoseleyMoseley – British physicist, arranged – British physicist, arranged

elements according to increasing elements according to increasing atomic numberatomic number His basic arrangement is still used todayHis basic arrangement is still used today The symbol, atomic number & mass are the basic The symbol, atomic number & mass are the basic

items included in the periodic tableitems included in the periodic table

The periodic table displays the The periodic table displays the symbolssymbols and and namesnames of the elements, along with of the elements, along with atomic atomic numbernumber and and average atomic massaverage atomic mass

Squares in the Periodic TableSquares in the Periodic Table

Black symbol = solid

Red symbol = gas @ Blue symbol = liquid

All @ 25º C

There are other possible There are other possible arrangements. How about a:arrangements. How about a:

SpiralSpiral Periodic Table Periodic Table

The Periodic Table:The Periodic Table:

The periodic table allows you to easily compare the properties of one element to another

Your “best friend” is an arrangement of elements in which they are separated into groups based on a set of repeating properties.

The Periodic LawThe Periodic Law

When elements are arranged in order of When elements are arranged in order of increasing atomic number, there is a increasing atomic number, there is a periodic periodic repetitionrepetition of their physical and chemical of their physical and chemical properties.properties.

Horizontal rows = Horizontal rows = periodsperiodsRepeated properties in each rowRepeated properties in each row

There are 7 periodsThere are 7 periods

Vertical column = Vertical column = groupgroup (or family) (or family)Similar physical & Similar physical &

chemical chemical propertiespropertiesIdentified by number Identified by number

& letter& letter

Areas of the periodic tableAreas of the periodic table

Three classes of elements are: Three classes of elements are:

1) Metals 2) Nonmetals 3) Metalloids1) Metals 2) Nonmetals 3) Metalloids

MetalsMetals

1)1) MetalsMetals: electrical conductors, have luster, : electrical conductors, have luster, are ductile and malleable are ductile and malleable (in pink below)(in pink below)

NonmetalsNonmetals: generally brittle and dull, are poor : generally brittle and dull, are poor conductors of heat and electricity conductors of heat and electricity (in blue below)(in blue below)

Some nonmetals…Some nonmetals… are gases (O, N, Cl); are gases (O, N, Cl); are brittle solids (S, C); are brittle solids (S, C); one is dark red liquid (Br)one is dark red liquid (Br)

Notice the heavy, stair-step line…Notice the heavy, stair-step line…3)3) MetalloidsMetalloids:: border the lineborder the line

Their properties are Their properties are intermediateintermediate between between metals and nonmetalsmetals and nonmetals (in green below)(in green below)

1A

2A 3A 4A 5A 6A7A

8A

Elements in the 1A-7A groups are Elements in the 1A-7A groups are called the called the Representative ElementsRepresentative Elements Have very predictable properties and Have very predictable properties and

patterns of behaviorpatterns of behavior

Groups of elementsGroups of elementsGroup IA – Group IA – Alkali MetalsAlkali Metals

Are the most reactive metalsAre the most reactive metals Form a “base” when reacting with waterForm a “base” when reacting with water

Alkali Alkali MetalsMetals

Group 2AGroup 2A – – Alkaline Earth MetalsAlkaline Earth Metals Are the second most reactive metalsAre the second most reactive metals

Also form bases with water, but do not dissolve well; hence “earth metalsAlso form bases with water, but do not dissolve well; hence “earth metals””

Groups of ElementsGroups of Elements

Alkaline Alkaline Earth Earth MetalsMetals

Group 7AGroup 7A – – HalogensHalogens The most reactive non-metal groupThe most reactive non-metal group Means “salt-forming”Means “salt-forming”

Groups of elementsGroups of elements

The Halogen GroupThe Halogen Group

1)1) Group 8A-Group 8A- Noble GasesNoble Gases Previously called “inert gases” because they rarely take part in a Previously called “inert gases” because they rarely take part in a

reactionreaction Noble gases have a Noble gases have a completely fullcompletely full electron arrangement electron arrangement

Groups of elementsGroups of elements

Noble Noble

GasesGases

The “B” groups are called The “B” groups are called the the Transition ElementsTransition Elements

Lanthanide SeriesLanthanide SeriesActinide SeriesActinide Series

The “Inner Transition Metals” actually belong here

LaLa

AcAc

Crash Course Chemistry - The Periodic Table