124114499 periodic table periodicity

7/29/2019 124114499 Periodic Table Periodicity

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PERIODICITY


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Dimitri Mendeleev was the first scientist topublish an organized periodic table of theknown elements.


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The Periodic Law states: When arranged by increasing atomic

number, the chemical elements

display a regular and repeatingpattern of chemical and physicalproperties.


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Besides the 4 blocks of the table, there isanother way of classifying element:

Metals

Nonmetals Metalloids or Semi-metals. The following slide shows where each group

is found.


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Two Br atoms bonded together are 2.86angstroms apart. So, the radius of each atomis 1.43 .

2.861.43 1.43


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The trend for atomic radius in a groupis to go from smaller at the top tolarger at the bottom.

With each step down the group, anentirely new shell added to theelectron cloud, making the atomslarger with each step.


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The trend across a horizontal period isless obvious. Each step adds a proton and an

electron (and 1 or 2 neutrons). Electrons are added to existing shellsor subshells.


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The effect is that the more positivenucleus has a greater pull on theelectron cloud because the shieldingeffect remains the same.

As effective nuclear charge increases,the electron cloud is pulled in tighter.

The ENC is the positive charge that an

electron experiences from thenucleus.


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Atoms become smaller as we movefrom left to right across a period.

The closer an electron is to thenucleus, the more pull it feels. Thesmaller is the radius.

The shielding effect is Theattraction for electrons in theoutermost shell by the nucleus is

shielded by electrons in lowerenergy levels / inner shells.


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Withingroup the

atomic radiitend toincrease.

Atomic radii

actuallydecreaseacross arow.

Atomic Radii forMain Group

Elements (s,p)


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Hvapour = heat change when 1mole element is converted frmliquid to vapour @ its bp

Depends on 2 factors :1. Bonding metallic, covalent &

van der waals

2. Structure giant metallic, giantcovalent & simple molecular


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In P2, mp & bp increase from Li togiant molecule C Decrease abruptly to simplemolecule N until monoatomic Ne

The same trend is repeated for mp& bp across P3 mp & bp S > P since molecular size

S8 > P4


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Same trend also observed forenthalpies of vapourisation goingacross P2 & P3


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Giant metallic structureoMoving across metals in P2 & P3,

gradual in valence e- & nuclearcharge

oMetallic bonds become stronger

oConsequently mp, bp & HvapourincreasesoMetals change frm liq to vap; ALL

metallic bonds still exist have to be

broken, bp >> mpoP2 > P3 ; atomic radii of metals

smaller, stronger metallic bonds in P2


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Simple molecular structureo

All non-metallic elements in P2 & P3form small & discrete moleculesoCovalent bonds within molecules are

strong, but VdW forces between

molecules are weakomp, bp & Hvapour are lowoVdW forces as molecular size oP

4

, S8

, > N2

, O2

oCl2 > F2, AroAr > Ne


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Period2 Li Be B C N O F NeStructure Giantmetallic

Giantmetallic

Giantcovalent

Giantcovalent

Simplemolecule

Simplemolecule

Simplemolecule

MonatomicBonding Metallic Metallic Covalent Covalent Covalent Covalent CovalentFormula N2 O2 F2 NeType offorcebrokenon

melting/boiling

Metallicbond

Metallicbond

Covalentbond

Covalentbond

VdW VdW VdW VdW

Bonding, Structure and Properties

Period3 Na Mg Al Si P S Cl ArStructure Giantmetallic

Giantmetallic

Giantmetallic

Giantcovalent

Simplemolecule

Simplemolecule

Simplemolecule

MonatomicBonding Metallic Metallic Metallic Covalent Covalent Covalent CovalentFormula P4 S8 Cl2 ArType offorcebrokenonmelting/boiling

Metallicbond

Metallicbond

Metallicbond

Covalentbond

VdW VdW VdW VdW


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Structure and Properties


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Elements in P2 & P3 can be

classified into : Metals Metalloids Non-metals

Across P2 & P3; EC decreases Metal are good conductors in solid or

molten state ; delocalised electronspresent


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Non-metals are non-conductors ;

all valence e- used to form covalentbonds, no mobile electrons Noble gases stable octetarrangement ; no mobile e-

Metalloids are poor conductors EC of B, C(graphite) & Si higherthan non-metals but lower than

metals


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If an electron is given enough energy (inthe form of a photon) to overcome theeffective nuclear charge holding theelectron in the cloud, it can leave the

atom completely. The atom has been ionized or charged. The number of protons and electrons is

no longer equal. Lower IE, more easily its electrons can be

removed


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Def : The min energy required toremove 1 mol electron fromsubstance in gaseous state (measuredin kilojoules, kJ)

Ionization energy is always

endothermic, that is energy is addedto the atom to remove the electron. Depends on : Distance between outer e- andnucleus

Size of nuclear charge Shielding/screening effect


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IE decreases as atomic radiusincreases Distance btwn outer e- & nucleus ,

attraction of +ve charge nucleus for-ve charge e-

Nuclear charge , IE Attraction on -ve charge outer e- by

+vely charged nucleus stronger screening effect, IE

Valence e- are shielded from attractionof nucleus by many inner shellselectrons


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Exceptions : P2 ; Be, N > B, O

: P3 ; Mg, P > Al, S

a) as we go across P2 & P3, IE (1st) islarger ; ENC becomes higher as thenumber of protons in the nucleusof the atom becomes larger.

b) With an electron already in the

orbital there is repulsion between thetwo in the same orbital and it comesout with less IE.


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P2 ; Be : 1s22s2 B : 1s22s22p1P3 ; Mg : 1s22s23s2 Al: 1s22s22p63s23p1

More energy is required to remove anelectron from a fully filled sorbital than asingly occupied porbital

P2 ; N : 1s22s22p3 O: 1s22s22p4P3 ; P : 1s22s22p63s23p3 S: 1s22s22p63s23p4More energy is required to remove anelectron from a half filled porbital than a

partial filled porbital


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c) The trend going down a group

shows a decrease in the IE1 whichcorresponds to an increase in theatomic radius.

d) The 2nd, 3rd, and 4th ionizationenergies are those required to removethe 2nd, 3rd, and 4th electrons andso on.


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Increase because ions produced becomemore +ve as more electrons areremoved.

The atom has been ionized or charged. The number of protons and electrons is

no longer equal. Lower IE, more easily its electrons can be

removed


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Big jumpshows how

manyvalence

electrons


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Bigjump

Frm SIE, 19electrons

contain inthiselement,thus it is

K, with 3shells & 1valenceelectron

e- confg :1s22s22p63s23p64s1


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Eg 1 : The graph of log IE of elementsX is given above. Determine theelectron configuration & position ofX in the Periodic Table, hence its

identity.Sol : element X consists of 3 shells with 7

valence electrons 1s22s22p63s23p5P3, G17 ; Cl


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Eg 2 : Partial SIE of an element Q is as follows.

Determine the valence shell configuration &position of Q in the Periodic Table.

Ans : ns2 ; G2 (Period unknown since SIEpartially !!!)


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Reaction with oxygen Reaction with water Hydrolysis of oxides Acidic & basic properties of oxides


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Rx OxygenSodiumSodium burns with an orange flame toproduce the white solid.

MagnesiumMagnesium burns with an intense whiteflame to give white solid.


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AluminiumAluminium will burn if powdered, otherwise

the strong oxide layer inhibit the reaction.Sprinkle of aluminium powder into flame,white sparkles is produced. White aluminiumoxide is formed.

SiliconSilicon will burn if heated strongly. White solidsilicon dioxide is produced.


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PhosphorusWhite phosphorus catches fire

spontaneously in air, with a white flame andproducing clouds of white smoke - amixture of phosphorus(III) oxide andphosphorus(V) oxide.

In excess oxygen, the product is almostentirely phosphorus(V) oxide:


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SulphurSulphur burns on gentle heating with a pale

blue flame. It produces colourless sulphurdioxide gas.

In excess oxygen, some SO3 is also formed.

Chlorine no effect ; Cl2O (yellowish gas) &Cl2O7 (colourless liquid) prepared by other

means.


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Ability as Ox Agt & Rd AgtGood reducing agents (electron donors)@ Na, Mg, Al larger size & lower IEEg : Al used in thermite rx to extract Cr

by reducing Cr2O3

Good oxidising agent (electron

acceptors) @ P, S & Cl2 smaller size &higher IEEg : Cl2 oxidises Fe(II) to Fe(III)


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Reactions with oxygen

Which is which? Sulphur

MagnesiumSodium
http://images.google.co.uk/imgres?imgurl=http://www.chm.bris.ac.uk/motm/so2/images4.jpg&imgrefurl=http://www.chm.bris.ac.uk/motm/so2/so2v.htm&usg=__sUy3_eD3arZNmAf6maxezJpsUrU=&h=112&w=94&sz=3&hl=en&start=37&um=1&tbnid=uEgc3gy7r9cG-M:&tbnh=86&tbnw=72&prev=/images?q=sulphur+burning+in+oxygen&ndsp=20&hl=en&rlz=1T4ADBR_enCN303CN303&sa=N&start=20&um=1&newwindow=1http://images.google.co.uk/imgres?imgurl=http://www.circuitguy.com/gallery/mg3n2/norm/Mg3N2-02.jpg&imgrefurl=http://www.circuitguy.com/gallery/?gallery=1&img=2&usg=__VU3A2f22edMScn2cjtBHMs08-hM=&h=500&w=375&sz=21&hl=en&start=9&um=1&tbnid=r9D-hIb7pRJzvM:&tbnh=130&tbnw=98&prev=/images?q=magnesium+burning+in+oxygen&hl=en&rlz=1T4ADBR_enCN303CN303&sa=N&um=1&newwindow=1http://images.google.co.uk/imgres?imgurl=http://img3.ifilmpro.com/resize/image/stills/films/resize/istd/2718354.jpg&imgrefurl=http://www.spike.com/video/sodium-fire-water/2948452&usg=__Oc1GQiZHBivakW_A7bNLoXqBtts=&h=480&w=640&sz=101&hl=en&start=8&tbnid=OhTBEASKegSEiM:&tbnh=103&tbnw=137&prev=/images?q=sodium+burning+in+oxygen&gbv=2&hl=en&sa=G&newwindow=1


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2Na + 2H2O 2NaOH + H2(vigorously

cold water)Mg + 2H2O Mg(OH) 2 + H2 (vigorously steam)2Al + 3H2O Al2O3 + 3H2(vigorouslyout protective oxide layer)

Si + 2H2O SiO2 + 2H2 (slow steam @red heat)

P & S

do not react under any conditionsCl2 + H2O HCl + HClO(dissolvessparingly to form acids )

Rx Water


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Reaction of oxides with water

Na2O + H2O 2NaOH-dissolves readily in water, undergoeshydrolysis to produce OH-MgO sparingly soluble in water,

MgO + H2O Mg(OH)2-undergoes hydrolysis to produce OH-

Al2O3 - insoluble in water, no hydrolysis occur

Chemical properties of the oxides


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Reaction of oxides with water

SiO2 - insoluble in water, no hydrolysis occur

P4O10 + 6H2O 4H3PO4 (vigorously water)P4O6 + 6H2O 4H3PO3- Hydrolysis occur to produce H+

SO2 + H2O

H2SO3 (dissolves readily)SO3 + H2O H2SO4 (very exothermic)- Hydrolysis occur to produce H+,SO3 moreacidic than SO2Cl2O + H2O 2HClO (decompose to

light to produce HCl & O2)Cl2O7 + H2O 2HClO4


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Acid/base properties of oxidesNa2O dissolves in water to produce

strong alkaliNa2O + H2O 2NaOH

MgO dissolves slowly in hot dilute acidsMgO + H2SO4 MgSO4 + H2O


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Al2O3 dissolves slowly in hot dilute

mineral acids & hot, concentratedalkali (ionic compnd with covalentcharacter) to show amphoteric

natureBASE :

Al2O3+ 3H2SO4

Al2(SO4)3 + 3H2OACID:

Al2O3+ 2NaOH + 3H2O 2NaAl(OH)4


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Use of SO2 in Food Preservative-Widely used in food & beverageindustries.-Preservatives & antioxidant => mildreducing & acidic properties.-Prevent growth of bacteria & avoidrancidity of f&b


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124114499 periodic table periodicity

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