1.5 Atom Structure and the Periodic Table

7/21/2019 1.5 Atom Structure and the Periodic Table

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Particle

electron

neutronproton

Relative chargeRelativemass

Subatomic particles

Atoms are composed of three subatomic particles: protons

neutronsand electrons! "he two important properties of

these particles are mass and char#e:

-11/1840

01+11

"he mass of electrons is ne#li#ible when compared to the

mass of protons and neutrons so their mass is not included

when calculatin# the mass of the atom!


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Atomic number and mass number

"he mass numberof an atom is the number of protons

plus the number of neutrons and is represented b% the

s%mbol A!

&hen an atom is

represented b% its

s%mbol the massnumber and

sometimes the atomic

number are shown!

"he number of protons in an atom is known as the

atomic numberor proton number and is represented

b% the s%mbolZ!

mass

number (A)

atomic

number (Z)


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hat are isotopes!

atomic numberis the same

mass number

is di""erent

"he reacti(it% of different isotopes of an element is identical

because the% ha(e the same number of electrons!

#sotopesare atoms of the same element that contain

different numbers of neutrons!

"he different masses of the atoms means that ph%sical

properties of isotopes are sli#htl% different!

carbon-1$ carbon-1%


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#sotopes o" chlorine

About )'* of naturall%+occurrin# chlorine is chlorine+3' ,3'-l.

and 2'* is chlorine+3) ,3)-l.!

1) protons

1/ neutrons

1) electrons

1) protons

20 neutrons

1) electrons


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&eutronsProtons#sotope

#sotopes o" carbon

"here is also more than one isotope of carbon:

81$-

'13-

12-

All isotopes of carbon ha(e 6 protons and so ha(e 6

electrons!

Because chemical reacti(it% depends on the number of

electrons the reacti(it% of the isotopes of carbon is identical!


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hat)s the number!


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*eighing) atoms

ass spectrometr,is an accurate instrumental techniue

used to determine the relative isotopic mass,mass of each

indi(idual isotope relati(e to carbon+12. and the relati(e

abundance for each isotope! rom this the relative atomic

massof the element can be calculated!

ome uses of massspectrometr% include:

carbon+1$ datin#

detectin# ille#al dru#s forensic science

space eploration!



ass spectrometr,



Parts o" the mass spectrometer



Process o" mass spectrometr,


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ass spectra o" monatomic elements


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ass spectra o" diatomic elements



Process o" mass spectrometr,


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hat is relative atomic mass!

"he relative atomic mass,Ar. of an element is the mass of

one of its atoms relati(e to 1412 the mass of one atom of

carbon+12!

5ost elements ha(e more

than one isotope! "he Arof

the element is the a(era#e

mass of the isotopes takin#

into account the abundance ofeach isotope! "his is wh% the

Arof an element is freuentl%

not a whole number!

average mass o" an atom 1$

mass o" one atom o" carbon-1$

relative atomic mass

(Ar.



sing mass spectra to calculate Ar

"he mass spectrum of an element indicates the mass and

abundance of each isotope present! or eample the mass

spectrum of boron indicates two isotopes are present:

ow can this be used to calculate the Arof boron7

0

100

20

$0

60

/0

abundance(.

0 2 $ 6 / 10 12

m/2

103 ($0.

113 (80.



alculating Ar

5ost elements ha(e more than one isotope! "he relati(e

atomic mass of the element is the a(era#e mass of the

isotopes takin# into account the abundance of each isotope!

56ample7 hat is the Aro" boron!

8n a sample of boron 20* of the atoms are 10Br and /0*

are 11Br!

8f there are 100 atoms then 20 atoms would be 10Br and

/0 atoms would be 11Br!

"he relati(e atomic mass is calculated as follows:

Arof Br ,20 10. ; ,/0 11.

100

Aro" 3r 1098



alculating Aro" magnesium

56ample7 hat is the Aro" magnesium!

8n a sample of ma#nesium )9!0* of the ma#nesium

atoms are 2$5# 10!0* are 2'5# and 11!0* are 265#!

$9Add these (alues

and di(ide b% 100

(18: + $;0 + $8. / 100

Aro" g $49%

$4 ':90

$; 1090

$ 1190

19-alculate mass abundance

of each isotope



Arcalculations


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d l " t


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odels o" atoms

At


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?he 3ohr model o" the atom

8n 1900 5a >lanck

,right. de(eloped his

?@uantum theor% whichstates that ener#% eists

in fied amounts called

>uanta!

8n 1913 iels Bohr ,left.

applied >lanks theor% to

electrons! e proposed that electrons could onl% eist in

fied energ, levels!

"he main ener#% le(els are called principal energ, levels

and are #i(en a number called the principal >uantum

number (n.with the lowest in ener#% bein# 1!

h t i i i ti !


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hat is ioni2ation energ,!

#oni2ationis a process in which atoms lose or #ain electrons

and become ions!

?he "irst ioni2ation (#1. energ,o" an element is the energ,

re>uired to removeone electron "rom a gaseous atom9

(g. @ +(g. + e-(g.

Lookin# at trends in ioniCation ener#ies can re(eal useful

e(idence for the arran#ement of electrons in atoms and ions!

"he second ioni2ation (#$. energ,in(ol(es the remo(al of a

second electron:

+(g. @ $+(g. + e-(g.

# i ti d "i iti


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#oni2ation energ, de"initions

5 id " l l


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>lottin# the successive ioni2ation energiesof ma#nesium

clearl% shows the eistence of different ener#% le(els and

the number of electrons at each le(el!

uccessi(e ioniCation

ener#ies increase as more

electrons are remo(ed!

5vidence "or energ, levels

Lar#e Dumps in the ioniCation

ener#% re(eal where electrons

are bein# remo(ed from the

net principal ener#% le(elsuch as between the 2ndand

3rd and 10thand 11thioniCation

ener#ies for ma#nesium!

electron removed

io

ni2ationen

erg,

2

3

$

'

6

12th

11th

10th

9th

/th

)th

6th

'th

$th

3rd

2nd

1st

id " l l


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ore evidence "or energ, levels

"he first ioniCation ener#ies of #roup 2 elements also show

e(idence for the eistence of different principal ener#% le(els!

=(en thou#h the nuclear

char#e increases down the

#roup the first ioniCation

ener#% decreases!

element

"irstioni2ation

energ,

(=Amol-1

.

'00

600

)00

/00

900

Be 5# -a r Ba

"his means electrons are

bein# remo(ed from

successi(el% hi#her

ener#% le(els which liefurther from the nucleus

and are less attracted to

the nucleus!

$00

? d i "i t i i ti i


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?rends in "irst ioni2ation energies

5nerg, levels


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5nerg, levels


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5vidence "or sub levels


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5vidence "or sub-levels

"he first ioniCation

ener#ies for the elements

in period 3 show a#eneral increase!

All principal ener#% le(els contain one or more sub-levels

with different but eact ener#% (alues!

owe(er aluminiums

(alue is below that ofma#nesium! "his su##ests

that the third principal

ener#% le(el is not one

sin#le ener#% le(el!element

"irstioni2ationenerg,

(=

Amol-1.

600

/00

1000

1200

1$00

a 5# Al > Ar $00

i -l

1600

?he sub levels


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?he sub-levels

"here are four sub+le(els

labelled in order of

increasin# ener#%: s p dand "! =ach holds a

different number of

electrons!

ma6 no9 electronssub-level

1$f

10d

6p2s

$s $p $d $f

3s 3p 3d

2s 2p

1s

32$

1/3

/2

21

sub-levels ma6 no9

electrons

principal energ,

levelB n

=ach principal

ener#% le(el

contains a

differentnumber of

sub+le(els!

Cevels and sub levels


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Cevels and sub-levels

3loc=s o" the periodic table


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3loc=s o" the periodic table

Drder o" sub levels


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Drder o" sub-levels

?he Au"bau principle


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?he Au"bau principle

As part of his work on electron confi#uration iels Bohr

de(eloped the Au"bau principle which states how

electrons occup% sub+le(els!

?he Au"bau principlestates that the

loest energ, sub-levels are occupied "irst9

"his means the 1s sub+le(el

is filled first followed b% 2s

2p 3s and 3p!

owe(er the $s sub+le(el is

loerin ener#% than the 3d

so this will fill first!


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riting electron con"iguration


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riting electron con"iguration

5lectron con"iguration7 true or "alse!


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5lectron con"iguration7 true or "alse!

5lectron con"iguration o" transition metals


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5lectron con"iguration o" transition metals

Althou#h the 3d sub+le(el is in

a lower principal ener#% le(el

than the $s sub+le(el it isactuall% hi#her in ener#%!

56ample7 hat is the electron structure o" vanadium!

$%19 -ount number of electrons in atom

1s$$s$$p%s$%p4s$%d%$9ill sub+le(els rememberin#

$s is filled before 3d

"his means that the $s sub+le(el

is filled before the 3d sub+le(el!

5lectronic con"iguration7 atoms


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5lectronic con"iguration7 atoms

5lectron con"iguration o" ions


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5lectron con"iguration o" ions

&hen writin# the electron

confi#uration of ions it is

important to add or subtract theappropriate number of electrons!

Eor negativeions

addelectrons9

56ample7 hat is the electron structure o" D$-!

819-ount number of electrons in atom

1s$$s$$p%9ill sub+le(els as for unchar#ed atom

8 + $ 10$9Add or remo(e electrons due to char#e

Eor positive ions

removeelectrons9or non+transition metals the sub+

le(els are then filled as for atoms!

5lectronic con"iguration o" transition metal ions


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&hen transition metals form ions it is the $s electrons that

are remo(ed before the 3d electrons!

56ample7 hat is the electron structure o" &i$+!

$819 -ount number of electrons

in atom

1s$$s$$p%s$%p4s$%d8$9ill sub+le(els rememberin#

$s is filled before 3d

1s$$s$$p%s$%p%d849Eemo(e electrons startin#

with $s

5lectronic con"iguration o" transition metal ions

$%9 -ount number of electrons

to be remo(ed

5lectron con"iguration7 ions


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5lectron con"iguration7 ions


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5lectron orbitals


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5lectron orbitals

8t is impossible to eactl% locate the position of an electron

within an ener#% sub+le(el! B% measurin# the electron densit%

around the nucleus it is possible to define re#ions whereelectrons are most likel% to be found at an% one time! "hese

re#ions are called orbitals!

=ach ener#% sub+le(el has one or more orbitals each of

which can contain a maimum of two electrons!

ma6 no9

electrons

no9 orbitssub-level

1$)f

10'd

63p

21s

Shapes o" electron orbitals


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Shapes o" electron orbitals

?he Pauli e6clusion principle and spin


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?he Pauli e6clusion principle and spin

8t also introduces a propert% of electrons called spin which

has two states: ?up and ?down! "he spins of electrons in the

same orbital must be opposite i!e! one ?up and one ?down!

A spin diagramshows

how the orbitals are

filled! Frbitals are

represented b% suares

and electrons b% arrows

pointin# up or down!

?he Pauli e6clusion principlestates that each orbital

ma, contain no more than to electrons9

spin diagram

"ormagnesiumB

1s$$s$$p%s$

Rules "or "illing electrons


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Rules "or "illing electrons

&hen two electrons

occup% a p sub+le(el

the% could eithercompletel% fill the same

p orbital or half fill two

different p orbitals!

8f two electrons enter the same orbital there is repulsion

between them due to their ne#ati(e char#es! "he most stable

confi#uration is with sin#le electrons in different orbitals!

Fund)s rulestates that single electrons

occup, all empt, orbitals ithin a sub-level

be"ore the, start to "orm pairs in orbitals9

5vidence "or Fund)s rule


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5vidence "or Fund s rule

"he first ioniCation ener#ies for the elements in period 3 show

a #eneral increase!

element

"irst

ioni2ationenerg,

(GAmol-1

.

600

/00

1000

1200

1$00

a 5# Al > Ar

$00

i -l

1600owe(er sulfurs (alue

is below that of

phosphorus! As thehi#hest ener#%

electrons of both are in

the 3p sub+le(el this is

e(idence for Fund)s

rule!

5vidence "or Fund)s rule7 P vs9 S


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>hosphorus has three electrons in its 3p sub+le(el and

sulfur has four!

"he lower first ionisation ener#% for sulfur is because it has

a pair of electrons in one of the 3p orbitals! 5utual repulsion

between these two electrons makes it easier to remo(e one

of them!

phosphorus sul"ur

5lectron con"iguration o" r and u


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g

"he electron confi#urations of chromium and copper are

eceptions to the normal rules of orbital fillin#:

8n each case the $s orbital contains one electron! "his isbecause the $s and 3d sub+le(els lie (er% close to#ether in

ener#% and the 3d bein# either half full or completel% full is a

lower ener#% arran#ement!

1s$$s$$p%s$%p4s1%d;

chromium

1s$$s$$p%s$%p4s1%d10

copper

&ith lar#er atoms like this it can be useful to shorten the

electron arran#ement! -opper can be shortened to

HArI4s1%d10!

reating spin diagrams


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g p g


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hat)s the =e,ord!


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,

5nerg, levels and electrons


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g,

ultiple-choice >ui2


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p >


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hat is periodicit,!


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"he term periodicit,describes a repeatin# pattern in

properties of elements across periods of the periodic table!

"he Eussian chemist Gmitr%

5endelee( is credited with bein# the

creator of the first (ersion of the

periodic table! e obser(ed that whenthe elements are arran#ed in order of

atomic mass there are recurrin#

patterns in certain properties!

"he modern periodic table can be usedto anal%se trends in properties such as

atomic radiusacross periods and

down #roups!

hat is atomic radius!


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"he atomic radiusof an element is difficult to precisel% define

because of the uncertaint% o(er the siCe of the electron cloud!

e(eral definitions are used!

or non+metallic elements the

covalent radius is often used

as the atomic radius! "his is half

the internuclear distancebetween two identical atoms in

a sin#le co(alent bond!

covalent

radius

Fne definition is half the shortest internuclear distance found

in the structure of the element!

ore on atomic radius


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or non+bonded adDacent atoms ,e!#! in a co(alent cr%stal of

a non+metallic element. the van der aals radiusis used as

a (alue for atomic radius! "his is half the shortest internucleardistance between two similar non+bonded atoms!

van der

aals radius

or metallic elements the metallic radiusis often used as

the atomic radius! "his is half the shortest internuclear

distance between two adDacent atoms in a metallic bond!

?rends in atomic radius in period %


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?rends in atomic radius in period %


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"he atomic radius of the elements

across period 3 decreases!5lementAtomic

radius (nm.a

5#

Ali

>

-l

Ar

0!190

0!1$'

0!11/0!111

0!09/

0!0//0!0)9

0!0)1

owe(er more than 99* of the

atom is empt% space H thenucleus and electrons themsel(es

occup% a tin% (olume of the atom!

"his mi#ht seem counter+

intuiti(e because as the

numbers of sub+atomic particles

increase the radius mi#ht beepected to also increase!

#ncrease in proton number


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"he number of protons in the nucleus of the atoms

increases across period 3!

"his increase in the number of protons increases the

nuclear chargeof the atoms! "he nucleus has stron#er

attraction for the electrons pullin# them in closer and so

the atomic radius decreases across the period!

increased

nuclear chargepulls electrons

closer

11a 125# 13Al 1$i 1'> 16 1)-l 1/Ar5lementprotonnumber

hat is shielding!


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56plaining atomic radius in period %


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>roton number increases

across period 3 but

shieldin# remainsapproimatel% constant!

0!190

0!1$'

0!11/

0!111

0!09/

0!0//0!0)9

0!0)1

5lementAtomicradius(nm.

Proton

number

11

12

13

1$

1'

161)

1/

a

5#

Al

i

>

-l

Ar

"his pulls these electrons

closer to the nucleus and

results in a smaller radius!

"his causes an increase

in e""ective nuclearcharge leadin# to a

#reater attraction

between the nucleus and

the outermost electrons!

Atomic radius in period %


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Atomic radius7 true or "alse!


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hat is "irst ioni2ation energ,!


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#oni2ationis a process in which atoms lose or #ain electrons

and become ions!

?he "irst ioni2ation energ,o" an element is the energ,

re>uired to removeone electron "rom a gaseous atom9

"he first ioniCation ener#% is therefore a measure of the

stren#th of the attraction between the outermost electrons

and the nucleus!

"he first ioniCation ener#ies of the elements in periods 2

or 3 can #i(e information about their electronic structure!

(g. @

+

(g. + e

-


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"here is a general

increasein the first

ioniCation ener#iesacross period 3!

"he #reater attraction between the nucleus and the

outermost electrons means that more ener#% is reuired to

remo(e an electron!

a 5# Al i > -l Ar

element

$00

600

/00

1000

1200

1$00

1600

ioni2ationenerg,

(=Amol-1.

Across period 3 the

proton number

increases but the

amount of shieldin#

does not chan#e

"he effecti(e nuclear char#etherefore increases!

si#nificantl%!

?rend in "irst ioni2ation energ,7 e6ceptions


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"here are two eceptions to the #eneral trend in first

ioniCation ener#%: both aluminium and sulfur ha(e lower

ioniCation ener#ies than mi#ht be epected!

loer

ioni2ation

energies

than

e6pected

a 5# Al i > -l Ar

element

$00

600

/00

1000

1200

1$00

1600

ioni2ation

energ,(=Amol-1.

Eirst ioni2ation energ, o" Al vs9 g


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"he first ioniCation ener#% of aluminium is less thanthat

of ma#nesium e(en thou#h aluminium has a hi#her

nuclear char#e!

"he electron remo(ed when aluminium is ioniCed is in a 3p

sub+le(el which is hi#her in ener#% than the 3s electron

remo(ed when ma#nesium is ioniCed! Eemo(in# an

electron from a hi#her ener#% orbital reuires less ener#%!

magnesium aluminium

Eirst ioni2ation energ, o" S vs9 P


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"he first ioniCation ener#% of sulfur is less thanthat of

phosphorus e(en thou#h sulfur has a hi#her nuclear char#e!

"he hi#hest ener#% electron in both phosphorus and sulfur is

in the 3p sub+le(el! owe(er in sulfur this electron is paired

while in phosphorus each 3p orbital is sin#l% occupied!

utual repulsionbetween paired electrons means less

ener#% is reuired to remo(e one of them!

phosphorus sul"ur

#oni2ation energ, in period %


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#oni2ation energ, in period %


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Plot o" the melting and boiling points


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&aB g and Al7 melting and boiling points


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"he meltin# and boilin# points increase for the three metallic

elements from sodium to aluminium!

"his is because the

stren#th of the

metallic bondsincreases! 5ore

ener#% is needed to

break the stron#er

metallic bonds so

meltin# and boilin#points are hi#her!

0

'00

1000

1'002000

2'00

3000

temperatur

e(G.

a 5# Al

element

melting point

boiling point

&aB g and Al7 metallic bond strength


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"he increase in metallic bond stren#th from sodium to

aluminium is due to two factors:

19 harge densit,9"his is the ratio of an

ions char#e to its siCe! a;ions are

lar#e with a small char#e so ha(e a

low char#e densit%! Al3;ions are smaller

with a lar#er char#e and so ha(e ahi#her char#e densit%! "he% are

therefore more stron#l% attracted to the

delocaliCed electrons!

$9 &umber o" "ree electrons9odium has onefree electron per metal ion whereas

aluminium has three! "his leads to more

attractions that must be broken in aluminium!

Silicon


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ilicon has a macromolecular

structuresimilar to that of

diamond!

=ach silicon atom is

bonded to four

nei#hbourin# silicon atomsb% stron# co(alent bonds!

"hese must be broken in

order for silicon to melt!

"his reuires a lot of

ener#% so siliconIs meltin#

and boilin# points are hi#h!

Period % non-metals


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"he meltin# and boilin# points of phosphorus sulfur and

chlorine are much lower than those of silicon!

Breakin# these forces of attraction reuires much less

ener#% than breakin# co(alent bonds!

"his is because

the% ha(e a

simplemolecular

structurewithweak (an der

&aals forces

holdin# the

molecules to#ether!0

'00

1000

1'00

2000

2'00

3000

3'00

temper

ature(G.

a 5# Al i > -l Ar

element

Period % non-metals7 structure


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elting points in period %


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elting points in period %


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Documents

1.5 Atom Structure and the Periodic Table