Chapter 5 - Atomic Theory and Structure (for Entry)

8/2/2019 Chapter 5 - Atomic Theory and Structure (for Entry)

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Atomic Theory and Structure

Engr. Yvonne Ligaya F. Musico


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Learning Objectives1. Discuss the historical concept of atoms

2. State the premises of Daltons AtomicTheory

3. Identify the three most importantparticles of an atom.

4. Differentiate proton, neutron andelectron

5. Determine the atomic number and

mass number of an atom6. Calculate the isotopic mass and

isotopic abundances of different atoms


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TOPIC Evolution of the Different Atomic

Theories

Structure of Atom and Propertiesof Atom

First Slide Last Slide


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Evolution of Different AtomicTheories


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The History of the Discovery of the Atom

The Greek Model of the Atom

Daltons Atomic Theory

Thomson Model

Rutherford Model

Bohr Model Modern Atomic Theory


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Beginning with Democritus, wholived during the late 5th and early

4th centuries BC, Greekphilosophers developed a theoryof matter that was not based onexperimental evidence, but ontheir attempts to understand theuniverse in philosophical terms.


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According to this theory, all

matter was composed of tiny,indivisible particles called

atoms (from the Greek word

atomos, meaningindivisible).


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According to the ancient Greeks,

atoms were all made of the same

basic material, but atoms of

different elements had different

sizes and shapes


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The sizes, shapes, and

arrangements of a materials

atoms determined the materials

properties.


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Daltons Atomic TheoryLate 1700s - John Dalton-

England

Teacher- summarized results ofhis experiments and those ofothers.


Combined ideas of elements withthat of atoms.


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All matter is made of tiny

indivisible particles called

atoms.

Atoms of the same element are

identical, those of different

atoms are different.


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Atoms of different elementscombine in whole number

ratios to form compounds.

Chemical reactions involve the

rearrangement of atoms. Nonew atoms are created ordestroyed.


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Just How Small an Atom

Think of cutting a piece of lead intosmaller and smaller pieces

How far can it be cut?

An atom is the smallest particle of anelement that retains the properties ofthat element

Atoms-very small

still observable with properinstruments


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Thomson Model

J. J. Thomson - English

physicist. 1897

Made a piece of equipment

called a cathode ray tube.

It is a vacuum tube - all theair has been pumped out.


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J.Js Atomic Model

Plum Pudding model

-electrons distributed randomly in a diffuse positive

cloud.

-plum pudding model: raisins dispersed in

pudding.


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Thomsons Experiment

Voltage source

+-

Vacuum tube

Metal Disks


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Thomsons Experiment

Voltage source

+-


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Thomsons Experiment

Voltage source

+-


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Thomsons Experiment

Voltage source

+-


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Thomsons Experiment

Voltage source

+-

Passing an electric current makes a

beam appear to move from the

negative to the positive end


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Thomsons Experiment

Voltage source

+-


beam appear to move from the negative

to the positive end


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Thomsons Experiment

Voltage source

+-


beam appear to move from the negative

to the positive end


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Thomsons Experiment

Voltage source

By adding an electric field


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Thomsons Experiment

Voltage source


+

-


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Thomsons Experiment

Voltage source


+

-


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Thomsons Experiment

Voltage source


+

-


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Thomsons Experiment

Voltage source

+

-


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Thomsons Experiment

Voltage source


+

-


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Thomsons Experiment

Voltage source


+

-


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Thomsons Experiment

Voltage source

By adding an electric field he found that the

moving pieces were negative (electron)

+

-


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Other Particles

Proton - positively charged

pieces 1840 times heavier

than the electronby E.Goldstein

Neutron - no charge but the

same mass as a protonbyJ. Chadwick


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Rutherford Model

Ernest Rutherford -English

physicist. (1910)

Believed in the plum puddingmodel of the atom

Wanted to see how big they are.


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Rutherfords Experiment

Used radioactivity.

Alpha particles - positively charged

pieces- helium atoms minus

electrons

Shot them at gold foil which can be

made a few atoms thick.

When an alpha particle hits afluorescent screen, it glows.

Heres what it looked like


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Lead

blockUranium

Gold Foil

Fluorescent

Screen


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What he expected??

The alpha particles to pass

through without changing

direction very much.


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What he expected..


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Because


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He thought the mass was evenly

distributed in the atom



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Since he thought the

mass was evenly

distributed in the atom


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What he got


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How he explained it!

+

Atom is mostly empty.

Small dense,

positive piece

at center.

Alpha particles

are deflected by

it if they get close

enough.


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+


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Since most of the particles went

through, it was mostly empty space.

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

Small volume, big mass, big density.

This small dense positive area is the

nucleus.


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Bohr Model


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Bohr Model

Line-Emission Spectrum

ground state

excited state

ENERGY IN PHOTON OUT


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Bohr Model

e- exist only in orbits with

specific amounts of energy called

energy levels

Therefore

e-

can only gain or lose certainamounts of energy

only certain photons are produced


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Bohrs Model

1

23

45

6 Energy of photon

depends on thedifference in energylevels

Bohrs calculated

energies matchedthe IR, visible, andUV lines for the Hatom


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Other Elements

Each element has a unique bright-lineemission spectrum.

Atomic Fingerprint

Helium

Bohrs calculations only worked for

hydrogen!


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Subatomic Particles

Quarks

component

of protons& neutrons

6 types

3 quarks =

1 proton or

1 neutron

He


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Neutrons and protons are made up of

up quarks and down quarkstwo of

the six different kinds of quarks.

Quarks are unique among all

elementary particles in that they have

electric charges that are fractions of

the fundamental charge.

Quarks


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Quarks

All other particles have electric

charges of zero or of whole multiples

of the fundamental charge. Up

quarks have electric charges of +2/3.

Down quarks have charges of -1/3.

A proton is made up of two up quarks

and a down quark, so its electriccharge is 2/3 + 2/31/3, for a total

charge of +1.


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Quarks

A neutron is made up of an up quark

and two down quarks, so its electric

charge is 2/31/31/3, for a net

charge of zero.

Physicists believe that quarks are

true fundamental particles, so they

have no internal structure andcannot be split into something

smaller.


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Quarks

Physicists believe that quarks are

true fundamental particles, so they

have no internal structure and

cannot be split into something

smaller.

Microsoft Encarta Reference Library 2003. 1993-2002 Microsoft Corporation. All

rights reserved.


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Summary of the Model of the

Evolution of Atom


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Structure and Properties of

Atoms


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Structure and Properties of

Atoms

Properties of subatomic particles

Structure of atoms

Counting the pieces

Isotopes

LAST SLIDE


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Structure of Atoms

Electrons Negatively charge

Moving around the nucleus

Nucleus Protonspositively charge

Neutronsneutral


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Properties of Subatomic

Particles

Name Symbol Charge Relative

mass

Actual

mass (g)

Electron e- -1 1/1840 9.11 x 10-28

Proton p+ +1 1 1.67 x 10-24

Neutron n0 0 1 1.67 x 10-24


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Counting the Pieces

Atomic Number number of protons in the nucleus

number of protons determines kindof atom (since all protons are alike!)

the same as the number ofelectrons in the neutral atom.

Mass Number the number of protons + neutrons.

These account for most of mass


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Atomic Symbols

Show themass number and atomic number

Give the symbol of the element

mass number23 Na sodium-23

atomic number 11


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Atomic Number on the Periodic

Table

11

Na

Atomic Number

Symbol


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All atoms of an element have

the same number of protons

11

Na

11 protons

Sodium


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Subatomic Particles in Some

Atoms

16 31 65O P Zn

8 15 308 p+ 15 p+ 30 p+

8 n 16 n 35 n

8 e

-

15

e

-

30 e

-


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Learning Check?

YES NO

SKIP


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Solution

State the number of protons for atoms of

each of the following:

A. Nitrogen

2) 7 protons

B. Sulfur

2) 16 protons

C. Barium3) 56 protons


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Isotopes

Atoms with the same number of protons, but

different numbers of neutrons.

Atoms of the same element (same atomic number)

with different mass numbers

Isotopes of chlorine

35Cl 37Cl17 17

chlorine - 35 chlorine - 37


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Isotopes

Addison-Wesley Publishing Company, Inc.


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Isotopes of Hydrogen


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Relative Atomic Mass

12C atom = 1.992 10-23 g

atomic mass unit (amu)

1 amu = 1/12 the mass of a12C

atom

1 p = 1.007276 amu1 n = 1.008665 amu

1 e- = 0.0005486 amu


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Average Atomic Mass

weighted average of all isotopes

on the Periodic Table

round to 2 decimal places

100

(%)(mass(mass)(%) )

Avg.

AtomicMass


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Learning Check

Calculate the avg. atomic mass of

oxygen if its abundance in

nature is 99.76% 16O, 0.04%17O, and 0.20% 18O.


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Solution

Avg.AtomicMass

100(18)(0.20)(17)(0.04))(16)(99.76 16.00

amu


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Learning Check

Find chlorines average atomicmass if approximately 8 of every

10 atoms are chlorine-35 and 2are chlorine-37.


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Solution

Avg.AtomicMass

100

(37)(20)(35)(80)35.40 amu


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Learning Check

Gallium is a metallic element found in

small lasers used in compact disc players.

In a sample of gallium, there is 60.2% ofgallium-69 (68.9 amu) atoms and 39.8% of

gallium-71 (70.9 amu) atoms. What is the

atomic mass of gallium?


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Atomic Mass

Listed on the periodic table

Gives the mass of average atom of each element

compared to 12C

Average atom based on all the isotopes and their

abundance %

Atomic mass is not a whole number

Atomic mass is the weighted average mass of all

the atomic masses of the isotopes of that atom.

Na

22.99


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Solution

Using the periodic table, specify the

atomic mass of each element (round to the

tenths place):

A. calcium _40.1 amu _

B. aluminum _27.0 amu _

C. lead _207.2 amu_

D. barium _137.3 amu_

E. iron _55.8 amu__


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Finding an Isotopic MassAssign X and Y values:

X = % 10B Y = % 11B

Determine Y in terms of X

X + Y = 100

Y = 100 - X

Solve for X:

X (10.0) + (100 - X )(11.0) = 10.8

100 100

Multiply through by 10010.0 X + 1100 - 11.0X = 1080


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Finding an Isotopic Mass

Collect X terms

10.0 X - 11.0 X = 1080 - 1100

- 1.0 X = -20

X = -20 = 20 % 10B

- 1.0

Y = 100 - X

% 11B = 100 - 20% = 80% 11B


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Learning Check

Copper has two isotopes 63Cu (62.9 amu)

and 65Cu (64.9 amu). What is the %

abundance of each isotope? (Hint: Check

periodic table for atomic mass)

1) 30% 2) 70% 3) 100%


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Solution

2) 70%

Solution

62.9X + 6490 = 64.9X = 6350

-2.0 X = -140

X = 70%


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Chapter 5 - Atomic Theory and Structure (for Entry)

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