Structure of Atoms 2

7/21/2019 Structure of Atoms 2

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Chapter 2 STRUCTURE OF ATOMS

STRUCTURE OF ATOMS

Multiple Choice Questions

2.1 Atomic Structure

1. Formula for the distribution of electrons in KLM Shells is

a. n2 b. 2nc. 2 n2 d. 3n2

2. Rutherford bombarded a very thin gold foil about _________

thicness !ith ∝ "#articles.

a. $.$$$% cm b. $.$$$$% cmc. $.$$% cm d. $.$$$$$% cm

3. &eil 'ohr #ro#osed a model for an atom in

a. 1(11 b. 1(12c. 1(13 d. 1(1%

%. )tomic number of carbon is *. +he number of electrons in its

valence shell are

a. 2 b. %c. * d. ,

2.2 Atomic Structure

-. soto#es of an element can di/er in

a. &o. of #rotons b. &o. of electrons

c. &o. of neutrons d. )tomic number

*. +ritium 0hydrogen3 has ________ electrons.

a. 1 b. 2c. 3 d. ero

4. 5eavy !ater contains

a. 6rotium b. 7euteriumc. +ritium d. 'oth 6rotium and

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deuterium

,. 8hich isoto#e is used in atomic bombs

a. 923% b. 923-c. 923, d. )ll of these

(. d subshell can accommodate ma:imum _____________ electrons.

a. 2 b. *c. , d. 1$

1$. )fter 2# has com#letely ;lled< the additional electrons !ill ;ll

_______ subshell.

a. 3s b. 3#c. 3d d. 3f

11. Mshell can accommodate ma:imum electrons

a. 2 b. ,c. 1, d. 32

12. 5ydrogen has isoto#es

a. 1 b. 2c. 3 d. %

2.3 Electronic Confgurtion

13. 8hich are the subshells of Mshell

a. 2s < 2# b. 3s < 3#c. 3s < 3# < 3d d. 2s < 3s

1%. #sub shell contains ma:imum number of electrons.

a. 2 b. ,c. * d. 1$

1-. 27

13)l electronic con;guration in the subshell last occu#ied

a. 2s2 < 2#1 b. 3s2 < 3#1

c. 2s2 < 2#2 d. 3s2 < 3#2

1*. 8hich isoto#e is used to image brain=

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a. &a2% b. 123c. >o*$ d. >1%

14. 8hich isoto#e is used to trace the #ath of carbon in

#hotosynthesis=

a. >12 b. >13c. >1% d. )ll of these

1,. )fter 3s has com#letely ;lled< !hich subshell begins to ;ll=

a. %s b. 3#c. 3d d. %f

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1(. +he angular momentum of the electron is an integral multi#le of

a. n

2 π b.

h

2 π

c.

2n

h

d. ∆ E

2$. )s the n value increases the ______________

a. +he distance of electron from the nucleus increases

b. ?nergy of shell increases

c. 'oth a and b

d. &one of these

Ans!ers

1. c 2. b 3. c %. b -. c

*. a 4. b ,. b (. d 1$. a

11. c 12. c 13. c 1%. c 1-. b

1*. a 14. c 1,. b 1(. b 2$.

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STRUCTURE OF ATOMS

Short Questions

@. 1. "ht re ∝− particles #

)ns!erA ∝− particles are helium nuclei that are doubly #ositively

charged++¿

He¿

¿

@. 2. "ht re the conclusions o$ the Ruther$or%&se'periment#

)ns!erA Ruther$or% %re! the $ollo!ing conclusions(

1. Since maBority of the ∝− particles #assed through the foil un

deCected< most of the s#ace occu#ied by an atom must be

em#ty.2. +he deCection of a fe! ∝− particles through angles greater

than 90o sho!s that these #articles are deCected by

electrostatic re#ulsion bet!een the #ositively charged

∝− particles and the #ositively charged #art of atom.3. Massive ∝− particles are not deCected by electrons.

@. 3. "ht is the Ruther$or%&s Mo%el $or n tom#

)ns!erA Dn the basis of conclusions dra!n from his e:#eriments<

Rutherford #ro#osed a ne! model for an atom. 5e #ro#osed a

#lanetary model 0similar to the solar system for an atom. )n

atom is a neutral #article. +he mass of an atom is concentrated

in a very small dense #ositively charged region. 5e named this

region as nucleus. +he electrons are revolving around the

nucleus in circles. +hese circles are called orbits. +he centri#etal

force due to the revolution of electrons balances the

electrostatic force of attraction bet!een the nucleus and theelectrons.

@. %. )efne isotopes#

)ns!erA *sotopes re toms o$ n element !hose nuclei h+e the

sme tomic num,er ,ut %i-erent mss num,er. This is

,ecuse toms o$ n element cn %i-er in the num,er o$

neutrons. soto#es are chemically alie and di/er in their

#hysical #ro#erties.

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@. -. "rite $e! uses o$ isotopes.

)ns!erA Some of isoto#es are as follo!sA

i. Radioactive iodine 131 is used as a tracer in diagnosing thyroid

#roblem.ii. &a2% is used to trace the Co! of blood and detect #ossible

obstruction in the circulatory system.iii. odine123 is used to image the brain.iv. >obalt*$ is used irradiate cancer cells to shrin the tumors.

@. *. "ht %o ou men , shells/or,its n% energ le+el#

)ns!erA Shells or Or,its(

)ccording to 'ohrEs atomic theory< the electron in an atom

revolves around the nucleus in one of the circular #aths calledshells or orbits.

?ach shell is described by an n value. n can have values 1<2<3

and are designated as K< L< M etc. ?ach shell has a ;:ed

energy. So each shell is also called energy level.

@. 4. )escri,e the presence o$ su,0shells in shell#

)ns!erA Su,0shells(

) shell or energy level is sub divided into subshells or sub

energy levels. n value of a shell is #laced before the symbol for

a subshell. For instance<

n G 1< for K shell. t has only one subshell !hich as

re#resented by 1s.n G 2< L shell has t!o subshell< these are designated as

2s and 2#.n G 3< So M shell has 3 subshell called 3s< 3# and 3d.

Similarly & shell has %s< %#< %l and %f subshells.

@. ,. "ht re su,0shells#

)ns!erA ) shell or energy level is subdivided into subshells or sub


a subshell. For e:am#leA


re#resented by 1s.

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6G*&G

6G&G

6G&G


n G 2< for L shell< t has t!o subshells 2s and 2#. for M

shell n G 3< so it has three subshell called 3s < 3# and

3d.8hile & shell has %s< %#< %d and %f subshells.

@. (. Arrnge the $ollo!ing su,0shells in or%er o$ incresing

energ1s 2s 2p 3s 3p 3% s

)ns!erA 1s H 2s H 2# H 3s H 3# H %s H 3d

@. 1$. )efne the $ollo!ing(

. Electronic confgurtion

,. Au$ u 4rinciple

)ns!erA a +he arrangement of electrons in subshells is called as the

electronic con;guration.b )uf 'au 6rinci#le states that electrons ;ll the lo!est energy

subshell that are available ;rst. +his means electrons !ill

;ll ;rst 1s< then 2s< then 2# etc.

@. 11. "rite electronic confgurtion o$. 115 ,. 16Ar

)ns!erA a 11&a G 1s2 2s2 2#* 3s1

b 1,)r G 1s2 2s2 2#* 3s2 3#*

@. 12. "rite isotopes o$ the $ollo!ing elements(. Cr,on ,. Chlorine c.

Urnium

)ns!erA a >arbon has three isoto#es< carbon12< carbon13 and

carbon1%.

b >hlorine has t!o isoto#es< chlorine3- and chlorine34.

c 9ranium has three isoto#es< uranium23%< uranium23- anduranium23,

@. 13. Follo!ing fgure sho!s the incomplete structure o$

isotopes o$ cr,on. Cn ou complete it 7Acti+it 2.18.

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6G*&G,

6G*&G*

6G*&G4

6G14&G1,

6G14&G2$


12

6 >

13

6 >

14

6 >

)ns!erA >12 has * #rotons< * neutron and * electrons. >13 has *

#rotons< 4 neutrons and * electrons. >% has * #rotons< ,neutrons and * electrons.

12

6

> 13

6

> 14

6

>

@. 1%. Chlorine hs t!o isotopes. Figure sho!s the structure o$ isotopes o$ chlorine. Cn ou !rite isotope sm,ol $orech#

)ns!erA

*sotopes o$ chlorinesoto#es symbolsA&atural abundance 4-.44I 2%.23ISolution(

soto#e symbolsA 35

17 Cl

37

17 Cl

@. 1-. Fill in the ,ln9s. 7Acti+it 2.38

234

92U has ________ #rotons< ________ electrons and _____

neutrons

235


neutrons

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238


neutrons

)ns!erA

23492

U has __(2___ #rotons< __(2__ electrons and _ 1%2 _

neutrons

235

92U has __(2___ #rotons< __(2 __ electrons and _ 1%3 _

neutrons

238

92U has __(2___ #rotons< __(2__ electrons and _ 1%*

neutrons@. 1*. :i+e nmes n% sm,ols o$ isotopes o$ h%rogen.

)ns!erA 5ydrogen has three isoto#es.

5me Sm,ol

i. 5ydrogen " 1 1

1 H

ii. 5ydrogen " 2 2

1 H

iii. 5ydrogen " 3 3

1 H

;ong Questions

@. 14. )escri,e Ruther$or%&s e'periment. "ht conclusions he

%re! $rom the e'periment.)ns!erA Ruther$or%&s E'periment

Rutherford bombarded a very thin gold foil about $.$$$%cm

thicness !ith ∝− particles 0Figure. 5e used ∝− particles

obtained from the disintegration of #olonium. ∝− particles are

helium nuclei that are doubly #ositively charged 05eJJ. Most of

these #articles #assed straight through the foil. Dnly fe!

#articles !ere slightly deCected. 'ut one in 1 million !as

deCected through an angle greater than ($$

from their straight

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#aths. Rutherford #erformed a series of

e:#eriments using thin foils of other

elements. 5e observed similar

results from these e:#eriments.

Ruther$or% %re! the $ollo!ingconclusions(

1. Since maBority of the ∝− particles

#assed through the foil un

deCected< most of the s#ace

occu#ied by an atom must be em#ty.2. +he deCection of a fe! ∝− particles through angles greater

than 90o sho!s that these #articles are deCected by

electrostatic re#ulsion bet!een the #ositively charged∝− particles and the #ositively charged #art of atom.

3. Massive ∝− particles are not deCected by electrons.

@. 1,. "rite %e$ects in Ruther$or%&s tomic mo%el.

)ns!erA )e$ects in Ruther$or%&s Atomic Mo%el(

RutherfordEs model of an atom resembles our solar system. t

has follo!ing defectsA

i. >lassical #hysics suggests that electron being charged#article !ill emit energy continuously !hile revolving around

the nucleus. +hus the orbit of the revolving electron

becomes smaller and smaller until it !ould fall into the

nucleolus. +his !ould colla#se the atomic structure.ii. f revolving electron emits energy continuously it should

form a continuous s#ectrum for an atom but a line s#ectrum

is obtained.

@. 1(. E'plin the postultes o$ ohr&s tomic theor.

)ns!erA Min postultes o$ ohr&s tomic theor re s $ollo!s(

1. +he electron in an atom revolves around the nucleus in one of

the circular orbits. ?ach orbit has a ;:ed energy. So each orbit is

also called energy level.

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Figure Ruther$or%&s



6G1$&G11

6G1$&G1$


2. +he energy of the electron in an orbit is

#ro#ortional to its distance from the nucleus.

+he farther the electron is from the

nucleus< the more energy it has.

3. +he electron revolves only in those orbitsfor !hich the angular momentum of the

electron is an integral multi#le of h

2π

h

2 π

!here h is 6lanEs constant 0its value is 6.626×10−34

J . s .

%. Light is absorbed !hen an electron Bum#s to a higher energy

orbit and emitted !hen an electron falls into a lo!er energy

orbit. ?lectron #resent in a #articular orbit does not radiate

energy.

-. +he energy of the light emitted is e:actly eual to the di/erence

bet!een the energies of the orbits.

∆ E= E2− E

1

8here ∆ E is the energy di/erence bet!een any t!o orbits

!ith energies E1 and E

2

@. 2$. Figure sho!s ohr&s Mo%el $or t!o toms A n% . Cn

ou i%enti$ three similrities n% t!o %i-erences inthese toms# <usti$ tht these re toms o$ smeelement.

) G ' G

'ohrEs model for atom ) and atom ')ns!erA a Similarities

i. 'oth atoms have same number of #rotons.ii. 'oth the atoms have same number electrons.iii. 'oth have same atomic number.

b 7i/erences

i. 'oth have di/erent number of neutrons.ii. 'oth di/er in total number of #rotons and neutron. +his

means they have di/erent mass numbers.

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Figure ohr&s mo%el o$




Since both the atoms have same atomic number< they must be

the atoms of same element and are called isoto#es.

@. 21. "ht re isotopes. E'plin the isotopes o$ h%rogen.

)ns!erA +he !ord isoto#e !as ;rst used by Soddy. t is a ree !ord

isosN means same and to#eN means #lace.

*sotopes re toms o$ n element !hose nuclei h+e the

sme tomic num,er ,ut %i-erent mss num,er. This is

,ecuse toms o$ n element cn %i-er in the num,er o$

neutrons. soto#es are chemically alie and di/er in their

#hysical #ro#erties.

*sotopes o$ =%rogenA

5ydrogen has three isoto#esA

i. 5ydrogen1 06rotiumA5ydrogen " 1 06rotium has no neutron. t has one #roton

and one electron. )lmost all the hydrogen is 5ydrogen " 1.

ts symbol is1

1 H

ii. 5ydrogen " 2 07euteriumA5ydrogen " 2 07euterium has one neutron and one #roton

and one electron. ts symbol is2

1 H

iii. 5ydrogen " 3 0+ritiumA5ydrogen " 3 0+ritium has t!o neutrons< one #roton and

one electron. ts symbol is3

1 H

@. 22. :i+e nmes n% sm,ols o$ isotopes o$ cr,on. ;ist someo$ their properties.

)ns!erA Cr,on hs three isotopes.

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i. >arbon " 12t has si: neutrons< si: #roton and si: electrons. ts symbol is

12

6C

ii. >arbon " 13

t has seven neutrons< si: #roton and si: electrons. ts symbol is13

6C

iii. >arbon " 1%t has eight neutrons< si: #roton and si: electrons. ts symbol is

14

6C

4roperties o$ isotopes o$ Cr,on(

7i/erent forms of carbon are blac or grayish blac solids

e:ce#t diamond. +hey are odourless and tasteless. +hey have

high melting and boiling #oints and are insoluble in !ater.

@. 23. :i+e nmes n% sm,ols o$ isotope o$ chlorine. "ritetheir properties. )r! %igrmmtic s9etches o$ isotopes o$ chlorine.

)ns!erA *sotopes o$ chlorine(

+here are t!o natural isoto#es of chlorine< chlorine3- and

chlorine34.

Chlorine03>()n atom of cholorine3- has 14 #rotons and 1, neutrons.

>hlorine3- occurs in nature about 4-I. ts symbol is35

17Cl

Chlorine03?(

)n atom of cholorine34 has 14 #rotons and 2$ neutrons.

>hlorine34 occurs in nature about 2-I. ts symbol is37

17Cl

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6G14&G1,

6G14&G2$


4roperties o$ isotopes o$ Chlorine(

>hlorine is a grayish yello! gas !ith shar# #ungent irritating

smell. t is faily soluble in !ater.

*sotopes o$ Chlorine

@. 2%. ;ist uses o$ isotopes in %il li$e.)ns!erA Uses o$ *sotopes(

Stable and radioactive isoto#es have many a##lications in

science and medicines. Some of these are as follo!sA

i. Radioactive iodine " 131 is used as a tracer in diagnosing thyroid

#roblem.ii. &a " 2% is used to trace the Co! of blood and detect #ossible

constructions or obstructions in the circulatory system.iii. odine " 123 is used to image the brain.iv. >obalt " *$ is commonly used to irradiate cancer cells in the ho#e

of illing or shrining the tumors.v. >arbon " 1% is sued to trace the #ath of carbon in #hotosynthesis.vi. Radioactive isoto#es are used to determine the molecular structure

e.g. Sul#hur3- has been used in the structure determination of

thiosul#hate< S2D32 ion.

vii. Radioactive isoto#es are also used to study the mechanism of

chemical reactions.viii. Radioactive isoto#es are used to date rocs< soils< archaeological

obBects and mummies.

@. 2-. :i+e nmes n% sm,ols o$ isotopes o$ urnium. "ritetheir properties n% pplictions in %il li$e.

)ns!erA 9ranium has three isoto#es< 9ranium23%< 9ranium23- and

9ranium23,. Symbols of isoto#es of 9ranium areA

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234

92U <

235

92U <

234

92U

Stable and radioactive isoto#es have many a##lications in

science and medicines. Some of these are as follo!s.

4roperties n% pplictions o$ isotopes o$ urnium re s

$ollo!s(

i. 9ranium23- on ;ssion yields smaller nuclei< neutron and

energy. +he nuclear energy released by one g of uranium is

euivalent to chemical energy released by burning more than

14$$$g of coal.ii. 923- is used in nuclear reactor to generate electricity and in

atomic bombs.

iii. 923, decays into thorium23% and emits al#ha #article.iv. 923% is rare.

@. 2*. <usti$ tht isotopes o$ n element h+e similr chemiclproperties.

)ns!erA >hemical #ro#erties of an element de#end u#on the number of

#rotons and electrons. &eutrons do not tae #art in ordinary

chemical reactions. Since isoto#es of an element have same

number of #rotons and electrons< #ossess similar chemical

#ro#erties.

@. 24. "ht is ment , shells or or,its n% energ le+els."ht re su,0shells#

)ns!erA Shells(

)ccording to 'ohrEs atomic theory< the electron in an atom

revolves around the nucleus in one of the circular #aths called

shells or orbits. ?ach shell has a ;:ed energy. So each shell is

also called energy level. ?ach shell is described by an n value. ncan have values 1<2<3

8hen<

n @ 1 it is K shelln @ 2 it is L shelln @ 3 it is M shell etc.

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)s the value of n increases distance of electron from the nucleus

and energy of the shell increases.

Su,0shells(

) shell or energy level is sub divided into subshells or sub


a subshell. For instance


re#resented by 1s.For L shell n G 2< L shell has t!o subshell< these are

designated as 2s and 2#.For M shell n G 3< So M shell has 3 subshell called 3s< 3# and

3d. 8hile & shell has %s< %#< %d and %f subshells.

s subshell can accommodate ma:imum 2 electrons.# subshell can accommodate ma:imum * electrons.d subshell can accommodate ma:imum 1$ electrons.f subshell can accommodate ma:imum 1% electrons.

@. 2,. )escri,e the electronic confgurtion o$ frst 12elements.

)ns!erA Electronic Confgurtion o$ First 12 Elements.

First 12 elements in the table areA 5< 5e< Li< 'e< '< >< &< D< F< &e<&a and Mg

5ydrogen has atomic number 1. So it has only one electron that

!ill occu#y lo!est energy subshell 1s. +he electronic

con;guration of 5 is 1s1.

5elium has atomic number 2< so it has t!o electrons. Since s

subshell can accommodate t!o electrons< so electronic

con;guration of 5e is 1s2.

Lithium has atomic number 3< so it has three electrons< t!o !ill

;ll 1s subshell and one 2s subshell. So electronic con;guration

of Li is 1s2 2s1.

'eryllium has atomic number %< so it has four electrons. +!o of

these electrons go into 1s subshell and t!o !ill go to 2s sub

shell. +hus electronic con;guration of 'e is 1s2 2s2.

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6G*&G*

6G14&G1,


Dnce 2s subshell is ;lled< the 2# subshell begins to ;ll. 2# sub

shell can hold ma:imum * electrons. So ne:t si: elements !ill

have con;guration in !hich 2# subshell !ill be #rogressively

;lled. +herefore< these elements !ill have follo!ing electronic

con;guration.

-' G 1s22s22#1

*' G 1s22s22#2

4' G 1s22s22#3

,' G 1s22s22#%

(' G 1s22s22#-

1$' G 1s22s22#*

)fter 2# has com#letely ;lled< the additional electrons !ill ;ll 3s

subshell< so electronic con;guration of &a O Mg !ould be

11&a G 1s22s22#*3s1

12Mg G 1s22s22#*3s2

SE;F ASSESSME5T EERC*SES

SE;F B ASSESSME5T

EERC*SE 2.1

)r! ohr&s Mo%el $or the $ollo!ing toms in%icting the

loction $or electrons protons n% neutrons.

. Cr,on 7Atomic 5um,er @ mss 5um,er @ 128,. Chlorine 7Atomic 5o. 1? Mss 5o. 3>8c. Cr,on 7Atomic 5um,er @ mss 5um,er @ 128

. Cr,on 7Atomic 5um,er @ mss 5um,er @ 128

Solution(

&umber of electrons G *&umber of #rotons G *&umber of neutrons G 12 " * G *

,. Chlorine 7Atomic 5o. 1? Mss 5o. 3>8

Solution(

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&umber of electrons G 14&umber of #rotons G 14&umber of neutrons G 3- " 14 G 1,

SE;F B ASSESSME5T

EERC*SE 2.2

"rite the complete electronic confgurtion $or the

$ollo!ing elementsD

)l 0atomic number 13Si 0atomic number 1%6 0atomic number 1-

S 0atomic number 1*>l 0atomic number 14)r 0atomic number 1,

Solution(

13Al @ 1s22s22#*3s23#1

1Si @ 1s22s22#*3s23#2

1>4 @ 1s22s22#*3s23#3

1S @ 1s22s22#*3s23#%

1?Cl @ 1s

2

2s

2

2#

*

3s

2

3#

-

16Ar @ 1s22s22#*3s23#*

SE;F B ASSESSME5T

EERC*SE 2.3

"rite the electronic confgurtion $or the $ollo!ing

isotopes.

8.14

6C b.

35

17Cl c.

37

17C l

Solution(

8.14

6C G 1s22s22#2

,8.35

17C

35

17Cl G 1s22s22#*3s23#-

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c8.37

17Cl G 1s22s22#*3s23#-

SOC*ET T=EC=5O;O: A5)

SC*E5CE

@. 1. E'plin ho! interprettions o$ e'perimentl results o$ other scientists help chemist to $ormulte ne!e'plntion n% ne! theories.

)ns!erA Rutherford !as the ;rst scientist !ho #ro#osed ;rst atomic

model of an atom. 5e suggested that all of the #ositive charge

and most of the mass of the atom is concentrated in the

nucleus. +he remaining volume of the atom is occu#ied by

electrons that revolve around the nucleus in circles called orbits. +hese suggestions remained unchallenged. 'ut his model could

not e:#lain the stability of an atom and line s#ectrum for an

atom. 'ohr lea#ed over diPculty by using @uantum +heory of

Radiation that !as #ro#osed by Ma: 6lan. 'ohr #ro#osed that

an electron moves around the nucleus in !ell de;ned circular

#aths called orbits. )n orbit has ;:ed energy. ?lectron #resent in

an orbit does not emit energy. 'ohr atomic theory e:#lains

nicely the stability of an atom and also e:#lains !hy an atom

gives line s#ectrum. 7evelo#ment of 'ohrEs atomic model

e:#lains ho! inter#retations of e:#erimental results of other

scientists hel# chemists to formulate ne! e:#lanations and ne!

theories.

@. 2. <usti$ tht pre+iling theories ,ring ,out chnges inthem.

)ns!erA 7altonEs atomic theory e:#lained data from many e:#eriments.

So it !as !idely acce#ted. 7iscovery of subatomic #articles andisoto#es #roved that some of the 7altonEs ideas about atoms

!ere not correct. Scientists did not discard his theory. nstead<

they revised the theory to tae into account ne! discoveries.

+his sho!s ho! #revailing theories bring about changes in

them.

E 4O*5TS

Ruther$or%&s Atomic Mo%el(

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• Rutherford #ro#osed a #lanetary model for an atom. +he

nucleus of an atom is com#osed of #rotons. +he electrons are

revolving around the nucleus in circles.

ohr&s Atomic Mo%el(

• )ccording to 'ohrEs atomic model< the electron in an atom

revolves around the nucleus in ;:ed circular orbits called shells.

?nergy is absorbed !hen an electron Bum#s to a higher energy

orbit and emitted !hen an electron falls into a lo!er energy

orbit.

*sotopes(

• soto#es are atoms of an element that di/er in the number of

neutrons.

•235

92U isoto#e is used in nuclear reactors and atomic bombs.

R%iocti+e isotopes(

• Radioactive isoto#es have many a##lications in science and

medicines such as illing cancer cells< diagnosing thyroid

#roblem< to image the brain< to detect obstruction in the

circulatory system< to date rocs soils< mummies etc.

Su,0shells(

• ) shell or energy level is divided into subshells.

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Electronic confgurtion(

• +he arrangement of electrons in sub "shells is called as the

electronic con;guration.

Au$ u 4rinciple(

• )ccording to the )uf 'au 6rinci#le< electrons ;ll the lo!est

energy levels ;rst.

REG*E" QUEST*O5S

1. Encircle the correct ns!er(

i. )ccording to 'ohr atomic modelA

a. ?ach orbit has ;:ed energy< so each orbit is called sub

energy level.b. +he energy of the electron is inversely #ro#ortional to its

distance from the nucleus.c. Light is absorbed !hen an electron Bum#s a lo!er energy

orbit.

d. +he further the electron is from the nucleus< the more

energy it has.

ii. >hlorine has t!o isoto#es< both of !hich have

a. Same mass number b. same number of neutrons

c. di/erent number of #rotons d. same number of electrons

iii. &umber of neutrons in27

13 M are

a. 13 b. 1% c. 24 d. 1-

iv. 8hich isoto#e is commonly used to irradiate cancer cells=a. odine123 b. >arbon1% c. >obalt*$ d. odine

131

v. M shell has subshellsA

a. 1s< 2s b. 2s< 2# c. 3s< 3#< 3d d. 1s< 2s< 3s

vi. ) subshell that can accommodate * electrons is=

a. s b. d c. # d. f

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vii. 11&a has electronic con;gurationA

a. 1s22s23s1 b. 1s22s22#4

c. 1s22s22#-3S2 d. 1s22s22#*3S1

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viii. Rutherford used _____ #articles in his e:#eriments.

a. 5e atoms b. 5eJ c. 5eJ2 d. 5e2

i:. 8hich of the follo!ing statement is not correct about isoto#es=

a. +hey have same atomic numberb. +hey have same number of #rotons

c. +hey have same chemical #ro#erties

d. +hey have same #hysical #ro#erties

:. 8hich isoto#e is used in nuclear reactors=

a. 923% b. 923, c. 923- d. )ll of

these

Ans!ers(

1. d 2. d 3. b %. c -. c*. c 4. d ,. c (. d 1$.

c

2. :i+e short ns!ers

i. )istinguish ,et!een shell n% su,0shell.

)nsA )ccording to 'ohrEs atomic theory< the electron in an atom

revolves around the nucleus in one of the circular #aths calledshells or orbits. Shells are re#resented by symbols< K< L< M etc.

) shell is subdivided into subshells designated by s< #< d and

f. For e:am#le< the ;rst shell< K has only one subshell called

1s< the second shell 0L has t!o subshells< 2s and 2# etc.

ii. An tom is electricll neutrl !h#

)nsA )n atom contains eual number of #ositively charged #rotons

and negatively charged electrons. +hese charges are eual buto##osite. So< an atom is electrically neutral.

iii. =o! mn su,0shells re there in 5 shell

)nsA For & shell< n G %< So it has four subshells< %s< %#< %d and %f.

i+. :i+e nottion $or su,0shells o$ M shell.

)nsA For M shell< n G 3. So M shell has three subshells designated

as 3s< 3# and 3d.

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+. ;ist su,0shells o$ M shell in or%er o$ incresing energ.

)nsA 3s H 3# H 3d.

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+i. Cn ou i%enti$ n tom !ithout 9no!ing num,er o$

neutrons in it#

)nsA Qes< !e can identify an atom from its atomic number or

number of #rotons in it. For e:am#le< di/erent isoto#es of >arbon< >12< >13< >1% have same number of #rotons< so

they all are >atoms.

3. The electronic confgurtions liste% re incorrect. E'plin

!ht mist9e hs ,een m%e in ech n% !rite correct

electronic confgurtions.

@ 1s22s22p3p2

@ 1s

2

2s

1

2p

1

H @ 1s22s22p>3p1

)nsA )ccording to )uf 'au #rinci#le< electrons ;ll the lo!est energy sub

shell that is available ;rst. +his means electron !ill ;ll ;rst 1s then

2s< then 2#< then 3s so on. s can hold 2< # can hold * electrons.

n @ 1s22s22p3p2< 2# is lo!er in energy then 3# and is

incom#lete< so electron !ill ;ll 2# ;rst.

>orrect electronic con;guration G 1s22s22#*

n @ 1s22s12p1< 2s is lo!er in energy then 2# and it can

accommodate one more electron.

>orrect electronic con;guration G 1s22s2

n H @ 1s22s22p>3p1< 2# is lo!er in energy then 3s and can hold

another electron.

>orrect electronic con;guration G 1s22s22#*

. "hich or,itl in ech o$ the $ollo!ing pirs is lo!er inenerg#

. 2s 2p

,. 3p 2p

c. 3s s

Ans( a. 2s< 2# +he energy of 2s H 2#

b. 3#< 2# +he energy of 2# H 3#

c. 3s< %# +he energy of 3s H %s

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6G1(&G2$

6G1%&G1%

6G1,&G21


>. )r! ohr&s Mo%el $or the $ollo!ing toms in%icting the

loction $or electron protons n% neutrons(

. 4otssium 7Atomic 5o. 1I Mss 5o. 3I8

,. Silicon 7Atomic 5o. 1 Mss 5o. 268

c. Argon 7Atomic 5o. 16 Mss 5o. 3I8

Ans( a. 6otassium 0)tomic &o. 1(< Mass &o. 3(

0K G 2< L G ,< M G ,< & G 1

b. Silicon 0)tomic &o. 1%< Mass &o. 2,

0K G 2< L G ,< M G %c. )rgon 0)tomic &o. 1,< Mass &o. 3(

0K G 2< L G ,< M G %

. "rite electronic confgurtion $or the $ollo!ing elements(

8.28

14Si ,8.

24

13 Mg c8.

27

13 Al %8.

40

18 Ar

Solution(

8.28

14Si G 1s22s22#*3s23#2

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,8.24

13 Mg G 1s22s22#*3s2

c8.27

13 Al G 1s22s22#*3s23#1

%8.40

18 Ar G 1s22s22#*3s23#*

?. )escri,e the contri,ution tht Ruther$or% m%e to the

%e+elopment o$ the tomic theor.

Ans( Rutherford !as the ;rst scientist !ho #ro#osed ;rst atomic model

of an atom. 5e #erformed a series of e:#eriment< in !hich he

bombarded thin gold foil of $.$$$%cm thicness !ith al#ha

#articles. 'ased on observations from these e:#eriments< hesuggested that all the #ositive charge and most of the mass of

atom is concentrated in the thin center called nucleus. +he

electrons are revolving around the nucleus in circles. +hese circles

are called orbits. +hese suggestions remained unchanged. 'ut his

model could not e:#lain stability of an atom and line s#ectrum for

an atom.

6. E'plin ho! ohr&s tomic theor %i-ere% $rom

Ruther$or%&s tomic theor.

Ans( RutherfordEs atomic model could not e:#lain the stability of an

atom and line s#ectrum for an atom. 'ohrEs lea#ed over this

diPculty by using @uantum theory of Radiation< !hich !as

#ro#osed by Ma: 6lan. 'ohr #ro#osed that an electron moves

around the nucleus in circular #aths called shells. ) shell has ;:ed

energy. ?lectron #resent in a shell does not emit energy. 'ohrEs

theory nicely e:#lains the stability of an atom and it also e:#lains

!hy an atom gives live s#ectrum.

I. )escri,e the presence o$ su,0shells in shell.

Ans( See @uestion &o. 2% 0long uestion section

1J. Stte the importnce n% uses o$ isotopes in +rious fel%

o$ li$e.

Ans( See @uestion &o. 22 0long uestion section

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11. The tomic num,er o$ n element is 23 n% its mss

num,er is >.

8 =o! mn protons n% electrons %oes n tom o$ this

element h+e#

,8 =o! mn neutrons %oes this tom h+e#

Ans( a. )s atomic number of this element is 23< it has 23 #rotons and

23 electrons

b )s its mass number is -*< it has -* " 23 G 23 neutrons.

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12. The tomic sm,ol o$ luminum is !ritten s27

13 Al . "ht

in$ormtion %o ou get $rom it#

Ans( 8e get follo!ing information.

i. ts atomic number is 13< so it has 13 #rotons and 13 electrons

ii. ts mass number is 24< so it has 24 " 13 G 1% neutrons

13. =o! testing pre+iling theories ,ring ,out chnges in

them.

Ans( See @uestion &o. 2 0Society< +echnology and Sciences

1. =o! e'perimentl results o$ some scientists help chemist

to $ormulte ne! theories n% ne! e'plntion.

Ans( See @uestion &o. 1 0Society< +echnology and Sciences

T=*5 TA5

1>. M02 is r%iocti+e isotope use% to %ignose restricte%,loo% circultion $or e'mple in legs. =o! mn electrons

protons n% neutrons re there in this isotope. Glence

shell electronic confgurtion o$ M is 3s1.

Ans( alence shell electronic con;guration of M in 3s1. +herefore< its

com#lete electronic con;guration is 1s22s22#*3s1

+otal &o. of electrons in M G 2J2J*J1 G 11

So< &o. of 6rotons in M G 11

)tomic number of M G 11Symbol M2% sho!s< mass number G 2%

∵ &o. of neutrons G 2% " 1 G 13

1. T!o isotopes o$ chlorine re35

17Cl n%

37

17Cl . =o! %o

these isotopes %i-er# =o! re the li9e#

Ans( 7i/erencesA

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35

17Cl

37

17Cl

1. ts mass &o. G 3-

2. t has 3- " 14 G 1,

neutrons3. ts #hysical #ro#erties are

di/erent from35

17Cl

1. ts mass &o. G 34

2. t has 34 " 14 G 2$ neutrons

3. ts #hysical #ro#erties are

di/erent from37

17Cl

Similrities(

1. 'oth have atomic no. G 14

2. 'oth have 14 #rotons and 14 electrons

3. 'oth have same electronic con;guration

%. 'oth have same chemical #ro#erties

1?. =o! mn electrons cn ,e plce% in ll o$ the su,0shells in

the n@2 shell#

Ans( 8hen n G 2< it is Lshell< !hich can accommodate , electrons. thas t!o subshells 2s and 2#< 2s !ill have 2 electrons and 2# !ill

have * electrons.

16. Mss num,er o$ n tom in%ictes totl num,er o$ protons

n% neutrons in the nucleus. Cn ou i%enti$ n tom

!ithout n neutron#

Ans( Qes< ordinary hydrogen called #rotium has only one #roton and one

electron. t has no neutron in its nucleus. )n atom is identi;ed by

its atomic number i.e. by number of #rotons or electrons.

1I. The t,le sho!s the nuclei o$ f+e %i-erent toms.

5me o$ tom 5um,er o$ 4rotons

5um,er o$ neutrons

A > C ?) ? ?

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E 6 6. "hich tom hs highest mss num,er#

,. "hich t!o toms re isotopes#

c. "hich tom hs lest num,er o$ electrons#

%. "hich tom !ill h+e electronic confgurtion

1s22s22p3.e. "hich o$ the tom contins the most num,er o$

electrons#

Ans( a. )tom ? has highest mass number. ts mass number is , J , G

1*

b. ' and > are isoto#es since they have di/erent number of

neutrons< but same number of electrons and #rotons.

c. )tom ? has least number of electrons i.e. -.

d. )tom 7 has 4 electrons. So its electronic con;guration is

1s22s22#3.

e. )tom ? has most number of electrons i.e. ,. )ll other atoms

have less than , electrons.

2J. 5turll occurring nitrogen hs t!o isotopes 501 n% 50

1> select isotope tht hs greter num,er o$ electrons.

Ans( soto#es an element have same number of electrons. So both the

isoto#e have same of electrons.

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Structure of Atoms 2

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