September 10, 2012

METHOD OF WRITING CHEMICAL FORMULAE

CRISS -CROSS METHOD
1. The symbols of the component radicals of the compound are written side by side.
2. Positive radicals are written left and negative radicals on the right.
3. The valencies of the radicals are written above the respective symbols.
4. The criss-cross method is applied to exchange the numerical value of valency of each radical and  it is written as subscript of the other radical.
5. The radical is enclosed in a bracket and the subscript is placed outside the lower right corner.
6. The common factor is removed.
7. If the subscript of the radical is one, it is omitted.
 
SOME IMPORTANT RADICALS
Monovalent
Bivalent
Positive
radicals
Negative
radicals
Positive
radicals
Negative
radicals
Lithium,Li+
Fluoride,F-
Beryllium,Be2+
Oxide,O2-
Sodium,Na+
Chloride,Cl-
Magnesium,Mg2+
Sulphide,S2-
Potassium,K+
Bromide,Br-
Calcium,Ca2+
Chromate,CrO42-
Rubidium,Rb+
Iodide,I-
Strontium,Sr2+
Dichromate,Cr2O72-
Caesium,Cs+
Hydroxide,OH-
Barium,Ba2+
Tetraborate,B4O72-
Ammonium,NH4+
Cyanide,CN-
Ferrous (Iron),Fe2+
Silicate,SiO32-
Silver,Ag+
Nitrate,NO3-
Zinc,Zn2+
Hydrogen Phosphate,HPO42-
Cuprous (copper),Cu+
Nitrite,NO-2
Cupric (copper),Cu2+


Acetate,CH3COO-
Mercuric,Hg2+
Oxalate,C2O42-
Hydrogen,H+
Hydride,H-
Manganous,Mn2+


Bicarbonate,HCO3-
Chromous,Cr2+
Carbonate,CO32-
Aurous (Gold),Au+
Bisulphate,HSO4-
Stannous (Tin),Sn2+
Sulphate,SO42-

Bisulphite,HSO3-
Plumbous (Lead),Pb2+
Sulphite,SO2-3

Chlorate,ClO3-
Cobaltous,Co2+
Thiosulphate,S2O32-

Hypochlorate,ClO-
Nickel(ous),Ni2+


Permanganate,MnO4-
Cadmium,Cd2+
Manganate,MnO42-

Perchlorate,ClO4-
Thionyl,SO2+


Metaborate,BO2-
Platinous(Platinum),Pt2+


Amide,NH-2



Ethoxide,C2H5O-



Cyanate,CNO-



Thiocyanate,CNS-



Isothiocyanate,NCS-



Azide,N3-




Trivalent
Tetravalent
Positive
radicals
Negative
radicals
Positive
radicals
Negative
radicals
Boron,B3+

Carbon,C4+
Carbide,C4 -
Nitogen,N3+
Nitride,N3-
Silicon,Si4+
Pyrophosphate,
P2O74-
Phosphorous,P3+
Phosphide,P3-
Platinic(Platinum),
Pt4+

Aluminium,Al3+

Titanium,Ti4+

Bismuth,Bi3+
Orthoborate,BO33-
Ceric,Ce4+

Ferric (Iron),Fe3+
Ferricyanide,
[Fe(CN)6]3-
Stannic(Tin),Sn4+
Ferrocyanide,
[Fe(CN)6]4-
Manganic,Mn3+
(Ortho)phosphate,
PO43-
Plumbic(Lead),Pb4+

Chromium(ic),Cr3+
Phosphite,PO33-


Auric(Gold),Au3+



Cobaltic,Co3+




  

Exercise
 Negative
Radicals
Chloride
Nitrate
Sulphate
Carbonate
Hydroxide
Oxide
Sulphide
Positive
Radicals
Cl-
NO3-
SO42-
CO32-
OH-
O2-
S2-
Hydrogen
H+
HCl






Sodium
Na+

NaNO3





Potassium
K+


K2SO4




Ammonium
NH4+



(NH4)2CO3



Magnesium
Mg2+




Mg(OH)2


Calcium
Ca2+





CaO

Zinc
Zn2+






ZnS
Aluminium
Al3+
AlCl3






Ferrous
Fe2+







Ferric
Fe3+







Cuprous
Cu+
CuCl






Cupric
Cu2+

Cu(NO3)2





Plumbous
Pb2+







Plumbic
Pb4+







Stannous
Sn2+







Stannic
Sn4+







Chromous
Cr2+


CrSO4




Chromic
Cr3+


Cr2(SO4)3




Mercurous
Hg22+
Hg2Cl2






Mercuric
Hg2+
HgCl2






Manganous
Mn2+




Mn(OH)2


Manganic
Mn3+







Silver
Ag+

AgNO3





Nickelous
Ni2+
NiCl2





NiS
Barium
Ba2+


BaSO4




Cobaltous
Co2+

Co(NO3)2





Cobaltic
Co3+







Aurous
Au+







Auric
Au3+
AuCl3






Platinic
Pt4+
PtCl4







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