esercitazione n° 2 · electronegativity, symbol χ, is a chemical property that describes the...
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MaurizioCasarin
ChimicaGeneraleedInorganica(CanaleL–Z)
Instructor:MaurizioCasarin
Address:MaurizioCasarin:ViaLoredan4,35131-Padova
Phonenumber:+39049-827ext.5164E-mailaddress:[email protected]
http://www.chimica.unipd.it/maurizio.casarin/pubblica/casarin.htm
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Metals tend to loseelectrons.
NaDNa++e-
Non-metalstendtogainelectrons.
Cl+e-DCl-
Reducingagents Oxidizingagents
WeusetheOxidationStatetokeeptrackofthenumberofelectronsthathavebeengainedorlostbyanelement.
OxidationStates
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Electronegativity, symbol χ, is a chemical property that describes the ability of an atom to attract electrons (or electron density) towards itself in a covalent bond (Pauling, 1932).
ELECTRONEGATIVITY
Electronegativity cannot be directly measured and must be calculated from other atomic or molecular properties. As it is usually calculated, it is not strictly an atomic property, but rather a property of an atom inamolecule.
Ed(HBr)=3.79eV;Ed(H2)=4.52eV;Ed(Br2)=2.00eV χBr–χH=0.73
χH=2.20bydefinition
PAULING
1 eV = 1.60217653(14)×10−19 J = 96.48538(2) kJ/mole
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PAULINGELECTRONEGATIVITY
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MULLIKAN(ABSOLUTE)ELECTRONEGATIVITY
χ=(IE+EA)/2(kJ/mol)
IE-(First)IonizationEnergy(XgX++e-)EA-ElectronAffinity(X-gX+e-)
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IE-(First)IonizationEnergy
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EA-ELECTRONAFFINITY
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The correlation between Mulliken electronegativities (x-axis,inkJ/mol)andPaulingelectronegativities(y-axis).
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The OXIDATION STATE or OXIDATION NUMBER is the real or hypothetical, integer or fractional charge an atom in a neutral or charged formula would acquire following (a) the conventional attribution of all the bonding electrons in
a bond to the more electronegative atom; (b) the equipartition of the bonding electrons between atoms
with the same electronegativity.
LithiumhydrideLiH
Li+ H-
χH=2.20;χLi=0.98
χH>χLi
OS(Li)=+1OS(H)=-1
χN=3.04;χH=2.20
χN>χH
OS(N)=-3OS(H)=+1
AmmoniaNH3
NH
HH
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1. Theoxidationstate(OS)ofanindividualatominafreeelementis0.2. ThetotaloftheOSinallatomsin: i. Neutralspeciesis0.ii. Ionicspeciesisequaltothechargeontheion.3. Intheircompounds,thealkalimetalsandthealkalineearthshaveOSof+1
and+2respectively.4. IncompoundstheOSoffluorineisalways–15. Incompounds,theOSofhydrogenisusually+1(exception:hydrides,-1)6. Incompounds,theOSofoxygenisusually–2(exeptions:peroxides,-1;
superoxides,-1/2;oxygenfluoride,F2O,+2).7. Inbinary(two-element)compoundswithmetals:i. HalogenshaveOSof–1,ii. Group16haveOSof–2andiii. Group15haveOSof–3.
RulesforOxidationStates
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Anions(-Q):Groups15,16,17(VA,VIA,VIIA)Cations(+Q):Groups1,2,3(IA,IIA,IIIA)
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AssigningOxidationStates.
Whatistheoxidationstateoftheunderlinedelementineachofthefollowing?a)P4;b)Al2O3;c)MnO4
-;d)NaH
a) P4 is an element. P OS = 0 .
b) Al2O3: O is –2. O3 is –6. Since (+6)/2=(+3), Al OS = +3.
c) MnO4-: net charge = -1, O4 is –8. Mn OS = +7.
d) NaH: net charge = 0, rule 3 beats rule 5, Na OS = +1 and H OS = -1.