Ch31!1!3 Atomic Models Megat

8/18/2019 Ch31!1!3 Atomic Models Megat

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Copyright © 2010 Pearson Education, Inc.

Chapter 31

Atomic Physics


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Units of Chapter 31

• 31.1 Early Models of the Atom

• 31.2 The Spectrum of Atomic Hydroen

• 31.3 !ohr"s Model of the Hydroen Atom


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At the end of the lesson# the students

should $e a$le to%

• &escri$e $riefly a$out Thomson# 'utherford and !ohr"sModel of atom

• Calculate the (a)elenths in !almer series of spectral lines

• Sol)e for speed# radius and enery of electron in !ohr or$it


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31*1 Early Models of the Atom

+.+. Thomson%

The electron (as disco)ered in 1,-.

The first modern model of the atom (as the

/plum puddin0 model tiny electrons

em$edded in a mass of positi)e chare.


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'utherford%

/solar system0 model of the atom electronsor$itin a small# positi)ely chared nucleus.


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31*2 The Spectrum of Atomic Hydroen

f (e loo at the liht emitted $y a lo(*pressure

as (hen su$4ected to a lare electric field# (e

find a series of indi)idual lines# called a linespectrum. This is the line spectrum of hydroen.


7/19Copyright © 2010 Pearson Education, Inc.

The (a)elenths in the )isi$le spectrum of

hydroen are i)en $y%

R is the 'yd$er constant%

This is called the !almer series of spectral lines.



To find all the series of hydroen# the

follo(in eneral formula can $e used%



31*3 !ohr"s Model of the Hydroen Atom

Assumptions of the !ohr model%

• The electron in a hydroen atom mo)es in a

circular or$it around the nucleus.

•

5nly certain or$its are allo(ed# (here theanular momentum in the nth allo(ed or$it is

•

Electrons in allo(ed or$its do not radiate.'adiation is emitted (hen an electron chanes

from one or$it to another# (ith fre6uency i)en

$y relation%



n order for an electron to mo)e in a circle of radius r at speed

v# the electrostatic force must pro)ide the re6uired centripetal

force. Hence%

Addin the anular momentum re6uirement i)es%

Su$stitute )n. Sol)in these e6uations for the allo(ed radii i)es%

Su$stitute r n.%



22

1 2 2

34 22

2 31 9 2 2 19 2

11

14

(6.626 10 . 1

4 (9.109 10 (!.9!! 10 . " (1.602 10

#.29 10

hr

mke

J s

kg N m C C

m

π

π

−

− −

−

= ÷

×= ÷× × × = ×

Calculate the radius for

the smallest or$it%



The total mechanical enery of an electron in a !ohr or$it is the

sum of its inetic and potential eneries. After some ale$raic

manipulation# and su$stitutin no(n )alues of constants# (efind%

E7ample%

n dou$ly ioni8ed lithium# a sinle electron or$its a lithium nucleus.

Calculate the minimum enery re6uired to remo)e this electron.

2

1 2

3(13.6 122

1 E eV eV = − = −



Summary of Chapter 31

• The plum puddin model had a positi)ely

chared /puddin0 em$edded (ith electrons.

• 'utherford sho(ed that the atom (as mostly

empty space# leadin to the solar system

model.

• E7cited atoms of hydroen emit liht at

specific (a)elenths%




• !ohr model% electrons mo)e in circular or$its

around the nucleus9 only certain anularmomentum )alues are allo(ed9 electrons do not

radiate (hen in allo(ed or$its9 radiation is

emitted (hen electrons 4ump from one enery

le)el to another.

• 'adii of allo(ed or$its%




• Enery of allo(ed or$its%


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TEST:2 (ill co)er on

these chapters and

su$topics.

Chapter 22% 22.3 or 22.;

Chapter 23% 23.1:

Chapter 2

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Ch31!1!3 Atomic Models Megat