MaurizioCasarin

ChimicaGeneraleedInorganica(CanaleL–Z)

Instructor:MaurizioCasarin

Address:MaurizioCasarin:ViaLoredan4,35131-Padova

Phonenumber:+39049-827ext.5164E-mailaddress:maurizio.casarin@unipd.it

http://www.chimica.unipd.it/maurizio.casarin/pubblica/casarin.htm

Metals tend to loseelectrons.

NaDNa++e-

Non-metalstendtogainelectrons.

Cl+e-DCl-

Reducingagents Oxidizingagents

WeusetheOxidationStatetokeeptrackofthenumberofelectronsthathavebeengainedorlostbyanelement.

OxidationStates

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

PAULINGELECTRONEGATIVITY

MULLIKAN(ABSOLUTE)ELECTRONEGATIVITY

χ=(IE+EA)/2(kJ/mol)

IE-(First)IonizationEnergy(XgX++e-)EA-ElectronAffinity(X-gX+e-)

IE-(First)IonizationEnergy

EA-ELECTRONAFFINITY

The correlation between Mulliken electronegativities (x-axis,inkJ/mol)andPaulingelectronegativities(y-axis).

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

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

Anions(-Q):Groups15,16,17(VA,VIA,VIIA)Cations(+Q):Groups1,2,3(IA,IIA,IIIA)

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.